copyright (c) Franz Inc.
AllegroServe is available for download as part of Allegro CL (see www.franz.com) or at https://github.com/franzinc/aserve/. See www.franz.com/support/documentation/current/doc/aserve/aserve.html for the latest available version of this document.
Starting the Server
Shutting Down the Server
Entity hook function
Directory Access Files
Generating a Computed Response
Request Object Readers and Accessors
CGI Program Execution
AllegroServe Request Processing Protocol
Running AllegroServe as a Service on Windows NT
Using International Characters in AllegroServe
AllegroServe is a webserver written at Franz Inc. AllegroServe is designed to work with the htmlgen system for generating dynamic html, as one of the big advantages of a web server written in Common Lisp is the ability to generate html dynamically. In this document we'll consider the web server and dynamic html generation to be parts of the same product.
The design goals of AllegroServe are:
Running AllegroServe requires that you
We mention publish twice to emphasize that you can publish urls before and after you start the server.
The function net.aserve:start is used to start the server running.
&key port host
listeners max-listeners chunking keep-alive server setuid setgid
debug proxy proxy-proxy cache restore-cache accept-hook ssl ssl-password
os-processes external-format compress
ssl-key ssl-password ssl-method test-ssl ca-file ca-directory verify max-depth)
If no arguments are given then start starts a multi-threaded web server on port 80, which is the standard web server port. If you are running this on Unix then you can only allocate port 80 if you are logged in as root or have made Lisp a set-user-id root program.
There are quite a few keyword arguments to start, but in practice you only need be concerned with :port and :listeners. The arguments have the following meanings:
(shutdown &key server save-cache)
This shuts down the web server given (or the most recently started web server if no argument is passed for server). If save-cache is given then it should be the name of a file to which the current state of the proxy cache will be written. The save-cache file will only contain in-memory information about the cache. The cache usually consists of disk files as well and in order to maintain the complete state of the cache these files must be saved by the user as well. The information in the save-cache file refers to the disk cache files so those disk cache files must exist and be in the same state and location should the user choose to restore the state of the cache.
Once the server is started it will accept requests from http clients, typically web browsers. Each request is parsed and then AllegroServe searches for an object to handle that request. That object is called an entity. If an entity is found, it is passed the request and is responsible for generating and sending a response to the client. If an entity can't be found then AllegroServe sends back a response saying that that request was invalid.
Publishing is the process of creating entities and registering them in the tables scanned by AllegroServe after a request is read.
A request from an http client contains a lot of information. The two items that determine which entity will handle the request are
A request contains other information and while that information isn't used to determine which entity will handle the request it can be used by the entity handling the request in any way it sees fit.
The following functions create entities and specify which requests they will handle. An entity is distinguished by the path and host values passed to the particular publish function. When a publish is done for a path and host for which there is already an entity assigned, the old entity is replaced by the new entity.
authorizer server timeout plist hook headers compress)
This creates an entity that will return the contents of a file on the disk in response to a request. The url and file must be given, the rest of the arguments are optional.. The arguments have these meanings:
The function that handles requests for files will respond correctly to If-Modified-Since header lines and thus minimizes network traffic.
This will work on Unix where the password file is stored in /etc.
(publish-file :path "/password" :file "/etc/passwd" :content-type "text/plain")
AllegroServe supplies many subclasses of entity which automatically generate a responses to requests. There are times when user code needs to run during the generation of a response by one of the built-in entity classes. For example you may wish to add or modify the headers that will be sent back with the publish-file's response. The entity hook function is called just before the with-http-body in the response function. At this point all the response headers have been specified but the hook function is free to change them or add new headers.
The entity hook function takes three arguments: req, ent and extra. Req and ent are the familiar http-request and entity arguments. Extra is usually nil but will be one of the following symbols to tell the hook function if it's being called in a special context.
|:illegal-range||request has asked for a range of bytes that is not present in the entity. As a result a "416 - Illegal Range Specified" response is being generated.|
|:in-range||request has asked for a range of bytes and that range is being returned.|
|:not-modified||request contains an "If Not Modified" header and AllegroServe is returning a "304 - Not Modified" response.|
indexes filter timeout plist publisher access-file
hook headers compress hidden-index-redirect)
publish-directory is used to publish a complete directory tree of files. This is similar to how web servers such as Apache publish files. AllegroServe publishes the files in the directory tree in a lazy manner. As files in the tree are referenced by client requests entities are created and published.
publish-directory creates a mapping from all urls whose name begins with prefix to files stored in the directories specified by the destinations. destination may either be a single directory or a list of directories to search. The host, port, remove, authorizer, plist, hook, headers and server arguments are as described above for publish-file. The timeout argument defaults as described in publish-file. The hook argument specifies what hook function should be put in the entities that publish-directory creates. The access-file argument names the access file name which will be used in this directory tree. When a request comes in for which there isn't an entity that matches it exactly, AllegroServe checks to see if a prefix of the request has been registered. If so, and if the resulting entity is a directory-entity as created by this function, then it strips the prefix off the given request and appends the remaining part of the request to the destination string. It then publishes that (normally using publish-file and computing the content-type from the file type). Next that file-entity is made to handle the request in the normal manner.
If a request comes that maps to a directory rather than a file then
AllegroServe takes special action. First AllegroServe ensures
that the request uri ends in a slash. If the request was http://foo.com/onedir/twodir
then AllegroServe will return a redirect response so the client now
asks for http://foo.com/onedir/twodir/
. Next AllegroServe tries
to locate an index file for that directory. The indexes
specifies a list of index files to search for. By default the
list consists of two
filenames "index.html" and "index.htm". If an index file is found
then the value of the hidden-index-redirect
argument is consulted. If it is nil then AllegroServe
returns a redirect to the index file, e.g http://foo.com/onedir/twodir/index.html.
If hidden-index-redirect is true then AllegroServe will return the contents of the index file from the request, effectively doing the redirection to the index file internally and invisibly to the client.
The value of the filter argument is a function of four values: req ent filename and info. req and ent are the request and entity objects that describe the current client request. filename is the name of a known file on the current machine which is being requested by the current request. info is the list of access information for this file.
If the filter returns nil then the normal operation is done by the directory-entity handler: the selected file is published and then the request to access it processed (and subsequent access using that url will just return the file and never go through the filter again).
If the filter chooses to handle the request for the file itself it must generate a response to the request and then return a non-nil value. To avoid subsequent calls to the filter for this file the filter may choose to publish a handler for this url. If the filter wants to forbid access to this file a handy way to to call (failed-request req) and the standard "404 Not found" will be sent back to the client.
The publisher argument can be used to specify exactly what happens when a request comes that's handled by the directory-entity and a file is located on the disk that matches the incoming url. Nomally a publish-file is done to add that file. You may want to publish some other kind of entity to represent that file. The publisher argument, if non-nil, must be a function of four arguments: req ent filename info. The filename is a string naming the file that's been matched with the request. info is the list of access information for this file. The publisher function must return an entity to be processed to send back a response. The publisher function may wish to publish that entity but it need not do so.
|Note: publish-directory is a more general function than its name implies. It looks at each url path for a match for prefix and if such a match is found the prefix is removed and replaced with destination. Thus is prefix is "/foo" and destination is "/bar" then a url path of "/foobaz/joe.html" would be converted to "/barbaz/joe.html". This is rarely useful but it does show that you have to be careful about the prefix and destination strings. It's usually the case that if the prefix string ends in "/" then the destination string should end in "/" (and vice versa). Thus a prefix of "/foo" would have a destination of "/bar" and a prefix of "/foo/" would have a destination of "/bar/".|
The compress argument
specifies the value to pass for the :compress
argument to publish-file
when an entity is located i the directories and a publish-file is done automatically.
When files are accessed and automatically published you may wish to set some of the parameters of the entity that is published. As mentioned above you can define a publisher function that has complete control in publishing the entity. A less powerful but easier to use alternative is to place access files in the directory tree being published. An access file specifies information that you want passed to the publisher function. You can modify these access files while the directory tree is published and their latest values will be used for publishing subsequent files. This is similar to they way Apache controls its publishing with .htaccess files (except that in AllegroServe once a file is published the access files have no effect on it).
The name of an access file in AllegroServe is controlled by the :access-file argument to publish-directory. We'll assume the name chosen is access.cl in this document. If no :access-file argument is given to publish-directory then no access file checking is done. When a file is about to be published all access files from the destination directory all the way down to the directory containing the file to be published are read and used. For example if the destination in a publish-directory was given as "/home/joe/html/" and an http request comes in which references the file "/home/joe/html/pics/archive/foo.jpg" then AllegroServe will check for access files at all of these locations and in this order
The information is collected as successive access files are read. The new information is placed before the existing information thus causing subdirectory access files to possibly shadow information in access files in directories above it. Also superdirectory access file information is automatically eliminated if it isn't marked as being inherited.
The publisher function receives the collected information and can do with it what it wishes. We'll describe what the built-in publisher function does with the information.
When we speak of information in access files we are purposely being vague. We define what information must look like and what the standard publisher function does with certain information but we allow users to define their own kinds of information and use that in their own publisher function.
Each access file consists of zero or more Lisp forms (and possibly lisp style comments). Each form is a list beginning with a keyword symbol and then followed by a property-list-like sequence of keywords and values. Nothing in the form is evaluated. The form cannot contain #. or #,. macros.
One information form is used by AllegroServe's directory publisher code to decide if it's permitted to descend another directory level:
(:subdirectories :allow allow-list :deny deny-list :inherit inherit-value)
As AllegroServe descends from the destination directory toward the directory containing the file to be accessed it stops at each directory level accumlates the access information and then tests to see if it can descend further based on the :subdirectories information. If it cannot descend into the next subdirectory it gives up immediately and a 404 - Not Found response is returned. See the section Allow Deny processing below for a description of how it uses the :allow and :deny values.
These other information forms are used by the standard publisher function. Each takes an :inherit argument which defaults to false. Information not given with :inherit t will be eliminated as AllegroServe descends directory levels.
|specifies a location-authorizer restriction on which machines can see published files. The value of the :patterns argument has the same form as the :patterns slot of a location-authorizer.|
|specifies a password-authorizer restriction on access to published files. See the password-authorizer documentation for a description of the :realm and :allowed arguments|
|specifies which files are visible to be published. To be visible a file must be allowed and not denied. What is tested is the filename only (that is the part after the last directory separator in the files's complete name). See below for the rules on how allow and denied is used.|
|specifies which mime types are to be associated with which file types. This list takes precedence over the built-in list inside AllegroServe. :types is a list of mime specifiers. A mime specifier is a list beginning with a string giving the mime type followed by the files types that should map to that mime type. A file type in a list (e.g. ("ReadMe")) refers to the whole file name rather than the type component.|
The :files and :subdirectories information are used to determine if a file or subdirectory of a given name is accessible. AllegroServe will collect all the access file information for the directory containing the file or subdirectory and for all directories above it up to the directory given as the destination argument to publish-directory. Information from superdirectories will only be used if :inherit t is given for that information.
The rule is it that a given name is accessible if it is allowed and not denied. That is the filename or directory name must match one of the allow clauses and none of the deny clauses. There may be multiple allow and deny clauses since there may be multiple information forms of the type :files or :subdirectories. Each allow or deny argument can be a string or a list of strings or nil (which is the same as that argument not being given). The strings are regular expressions (which are not exactly like unix shell wildcard filename expressions). In particular ".*" is the regular expression that matches anything.
The special cases are the following
Here is a sample access file:
; only connections to localhost will be
able to access the
(:ip :patterns ((:accept "127.1") :deny) :inherit t)
(:password :realm "mysite"
:allowed (("joe" . "mypassword")
("sam" . "secret"))
:inherit t) ; applies to subdirectories
; publish html and cgi files, but not those beginning with a period
(:files :allow ("\\.html$" "\\.cgi$") :deny ("^\\."))
; specify mime type for non-standard file extensions. Also
; specify that a file named exactly ChangeLog should be given
; mime type "text/plain"
(:mime :types (("text/jil" "jil" "jlc") ("text/plain" "cl" ("ChangeLog"))))
&key path host
port content-type function class format remove server
authorizer timeout plist hook headers)
This creates a mapping from a url to a computed-entity, that is an entity that computes its response every time a request comes in. The path, host, port, remove, server , authorizer, hook, headers and class arguments are as in the other publish functions. The timeout argument defaults to nil always. The content-type sets a default value for the response to the request but this can be overridden. The format argument is either :text (the default) or :binary and it specifies the kind of value that will be sent back (after the response headers, which are always in text). This value is only important if the response is generated in a particular way (described below). The value of the hook argument is stored in the entity created however the hook function will only be run if the function supplied makes use of it.
The function argument is a function of two arguments: an object of class http-request that holds a description of the request, and an object of class entity that holds this entity which is handling the request. This function must generate a response to the http request, even if the response is only that the request wasn't found.
format remove server authorizer timeout plist hook headers)
This is like publish except that it declares function to be the handler for all urls that begin with the string prefix. Note however that prefix handlers have lower priority than exact handlers. Thus if you declare a prefix handler for "/foo" and also a specific handler for "/foo/bar.html" then the specific handler will be chosen if "/foo/bar.html" is found in an http request. Typically a prefix handler is used to make available a whole directory of files since their complete names begin with a common prefix (namely the directory in which the files are located). If you want to publish a whole directory then you probably want to use publish-directory since it has a number of features to support file publishing. The value of the hook argument is stored in the entity created however the hook function will only be run if the function supplied makes use of it.
authorizer timeout hook headers)
Some web pages are created from information from various sources. publish-multi allows you to specify a sequence of places that supply data for the combined web page. The data for each page is cached by publish-multi so that minimal computation is required each time the page is requested.
The host, port, content-type, class, remove, server, authorizer, hook, headers and timeout arguments are the same as those of the other publish functions. The items argument is unique to publish-multi and is a list of zero or more of the following objects
Here's an example where we create a page from a fixed header and trailer page with a bit of dynamic content in the middle.
(publish-multi :path "/thetime"
:items (list "header.html"
#'(lambda (req ent old-time old-val)
(declare (ignore req ent old-time old-val))
"The time is "
"Lisp Universal Time")
There are a variety of ways that a response can be sent back to the http client depending on whether keep-alive is being done, chunking is possible, whether the response is text or binary, whether the client already has the most recent data, and whether the size of the body of the response is known before the headers are sent. AllegroServe handles the complexity of determining the optimal response strategy and the user need only use a few specific macros in the computation of the response in order to take advantage of AllegroServe's strategy computation
Here's a very simple computed response. It just puts "Hello World!" in the browser window:
(publish :path "/hello"
:function #'(lambda (req ent)
(with-http-response (req ent)
(with-http-body (req ent)
(html "Hello World!")))))
This example works regardless of whether the request comes in from an old HTTP/0.9 browser or a modern HTTP/1.1 browser. It may or may not send the response back with chunked transfer encoding and it may or may not keep the connection alive after sending back the response. The user code doesn't have to deal with those possibilities, it just uses with-http-response and with-http-body and the rest is automatic. The html macro is part of the htmlgen package that accompanies AllegroServe. In the case above we are being lazy and not putting out the html directives that should be found on every page of html since most browsers are accommodating. Here's the function that generates the correct html:
(publish :path "/hello2"
:function #'(lambda (req ent)
(with-http-response (req ent)
(with-http-body (req ent)
(:body "Hello World!")))))))
The function above generates: <html><body>Hello World!</body></html>.
The macros and functions used in computing responses are these:
(req ent &key timeout check-modified format response content-type trailers)
This macro begins the process of generating a response to an http request and then runs the code in the body which will actually send out the response. req and ent are the request and entity objects passed into the function designated to compute the response for the request. timeout sets a time limit for the computation of the response. If timeout is nil then the entity ent is checked for a timeout value. If that value is also nil then the timeout value is retrieved from the current wserver object using wserver-response-timeout. If check-modified is true (the default) then the last-modified time stored in the entity object will be compared against the if-modified-since time of the request and if that indicates that the client already has the latest copy of this entity then a not-modified response will be automatically returned to the client and the body of this macro will not be run. response is an object containing the code and description of the http response we wish to return. The default value is the value of *response-ok* (which has a code of 200 and a string descriptor "OK"). content-type is a string describing the MIME type of the body (if any) sent after the headers. It has a form like "text/html". If content-type isn't given here then the content-type value in the entity (which is set in the call to publish) will be used.
The format argument specifies whether the code that writes the body of the response will want to write :text (e.g. write-char) or :binary (e.g. write-byte) when it writes the data of the body of the response. Based on the value of the format argument, AllegroServe will create the correct kind of response stream. If format is not specified here it will default to the value specified when publish was called to create the entity. If not :format argument was passed to publish then :binary format is assumed. If :binary is specified then you can write both text and binary to the stream since Allegro's binary streams also support text calls as well. If you specify :text then you may end up with a stream that supports only text operations.
The trailers specifies which header lines will be found in the trailer instead.
It also allows one to specify a value for the trailer (which may be changed
using the set-trailers function). All trailers you intend to send must be declared here.
trailers is list of strings, symbols or a cons of a string or symbol and a string. For example:
(:foo "bar" (:baz . "123123") ("bof" . "456"))
Trailers, like headers, are denoted by keyword symbols, with names being all in the case of the lisp (lower case for Modern lisps and upper case for ANSi lisps). The conversion between strings denoting trailer and the keyword symbol is done by AllegroServe in the appropriate manner
An http response consists of a line describing the response code, followed by headers (unless it's the HTTP/0.9 protocol in which case there are no headers), and then followed by the body (if any) of the response. with-http-response doesn't normally send anything to the client. It only does so when it determines that the if-modified-since predicate doesn't hold and that it must send back a not-modified response. Thus is not enough to just call with-http-response in your response function. You must always call with-http-body inside the call to with-http-response.
(with-http-body (req ent &key format headers external-format) &rest body)
This macro causes the whole http response to be sent out. The macro itself will send out everything except the body of the response. That is the responsibility of the code supplied as the body form of the macro. In cases where there is no body to the response being sent it is still necessary to call with-http-body so that the other parts of the response are sent out, e.g. at a minimum you should put (with-http-body (req ent)) in the body of a with-http-response.
The body forms may not be executed! If the request is an http head request then the browser wants only the headers returned. The with-http-body macro will not evaulate the body forms. You must be aware of this and should never put code in the body form that absolutely must be executed when a request is given.
The headers argument is a list of conses, where the car is the header name (a keyword symbol) and the cdr is the header value. These headers are added to the headers sent as part of this response.
Within the body forms the code calls (request-reply-stream req) to obtain a stream to which it can write to supply the body of the response. The external-format of this stream is set to the value of the external-format argument (which defaults to the value of *default-aserve-external-format*). The variable *html-stream* is bound to the value of (request-reply-stream req) before the body is evaluated. This makes it easy to use the html macro to generate html as part of the response.
Note: there used to be a :format argument to with-http-body. That argument was never used by with-http-body. The :format argument has been moved to with-http-response so that it can now have an effect on the stream created.
(get-request-body request &key external-format)
Return the body of the request as a string. If there is no body the return value will be an empty string. The result is cached inside the request object, so this function can be called more than once while processing a request. The typical reason for there to be a body to a request is when a web browser sends the result of a form with a POST method. The octets that make up the body of the request are converted to a string (and then cached) using the :octets external format as this is the appropriate external format if the request body contains a list of form values.
If an external-format is specified the body is reconverted to a string using the given external-format and then returned from this function. This reconversion does not affect the cached value.
(get-request-body-incremental request function &key buffer)Reads the body of a PUT or POST request and passes it to a function given by the caller. The function should take two arguments: vector and count. The vector is a simple-array of (unsigned-byte 8) and count is the number of bytes of data in the vector. The final time the function is called the value of count will be zero indicating there is no more data to follow. The same vector will be passed on each call.
The caller can pass in a simple-array of (unsigned-byte 8) as the value of the :buffer argument. If no buffer is supplied by the caller one will be allocated by the function.
This function or get-request-body can be called but not both.
This function treats the body of the request as a sequence of bytes. If you wish to convert it to a string you'll need to collect the whole body and call octets-to-string with the appropriate external format.
(header-slot-value request header-name)
Return the value given in the request for the given header-name (a keyword symbol). If the header wasn't present in this request then nil will be returned. header-slot-value is a macro that will expand into a fast accessor if the header-name is a constant naming a known header slot
In older versions of aserve the header-name was a string..
(reply-header-slot-value request header-name)
Return the value associated with the header header-name in the reply sent back to the client. This function is setf'able and this is the preferred way to specify headers and values to be sent with a reply.
(request-query request &key uri post external-format)
Decode and return an alist of the query values in the request. Each item in the alist is a cons where the car is a string giving the name of the argument and the cdr is a string giving the value of the argument.
The query string is in one or both of two places:
request-query will by default look in both locations for the query string and concatenate the results of decoding both query strings. If you would like it to not check one or both of the locations you can use the :uri and :post keyword arguments. If uri is true (and true is the default value) then the query string in the uri is checked. If post is true (and true is the default value) and if the request is a POST then the body of the post form will be decoded for query values.
The external-format is used in the conversion of bytes in the form to characters. It defaults to the value of *default-aserve-external-format*.
A query is normally a set of names and values.
http://foo.com/bar?a=3&b=4 yields a query alist (("a" . "3") ("b" . "4")).
If a name doesn't have an associated value then the value in the alist is the empty string.
http://foo.com/bar?a&b=&c=4 yields a query alist (("a" . "") ("b" . "") (c . "4"))
(request-query-value key request &key uri post external-format test)
This combines a call to request-query to retrieve the alist of query keys and values, with a call to assoc to search for the specific key, and finally with a call to cdr to return just the value from the assoc list entry. The test argument is the function to be used to test the given key against the keys in the assoc list. It defaults to #'equal.
If the given key is not present in the query nil is returned. If the given key is present in the query but doesn't have an associated value then the empty string is returned.
(set-trailers req-or-stream trailers)
Set values for the trailers sent after the response.
req-or-stream can be a request object or a stream. If a request object is passed then the reply stream for the request is used.
trailers is an assoc list.
The keys are the trailer names and the values are strings.
((:x-frob . "frib") (:content-type "text/plain"))
You can only specify values for trailers that you've already declared with the trailers argument to with-http-response. Trailers can only be sent if the response uses chunked transfer encoding but that is the standard encoding for HTTP/1.1 so this is rarely going to be an issue. You can use the can-set-trailers-p function to check if it's possible to set the trailers for this request. If set-trailers cannot set the trailers it does nothing.
(can-set-trailers-p req-or-stream)Return true if the set-trailers function can be used to set the trailers for this response. Trailers can only be set for chunking streams, or gzip streams which send their data to chunking streams. It's very likely that trailers can be set. This function allows you to test be sure.
Every request has zero or or more request
variables. A request variable is named by a lisp
string. The value of a request variable can be any
Initially a request has zero request variables.
(request-variable-value req "name")
Return the value of the request variable named "name". Return nil if there is no such request variable.
You can use (setf
(request-variable req "name") value) to set the value of a
The request object contains information about the http request being processed and it contains information about the response that is being computed and returned to the requestor. The following functions access slots of the request object. Those with names beginning with request-reply- are accessing the slots which hold information about the response to the request. When a function is listed as an accessor that means that it can be setf'ed as well as used to read the slot value.
(request-method request) - reader - a keyword symbol naming the kind of request, typically :get, :put or :post.
(request-uri request) - reader - a uri object describing the request. If the request contains a "Host:" header line then the value of this header is placed in the uri-host and uri-port slots of this uri object.
(request-protocol request) - reader - a keyword symbol naming the http protocol requested. It is either :http/0.9, :http/1.0 or :http/1.1.
(request-protocol-string request) - reader - a string naming the http protocol requested. It is either "HTTP/0.9", "HTTP/1.0" or "HTTP/1.1".
(request-socket request) - reader - the socket object through which the request was made and to which the response must be sent. This object can be used to determine the IP address of the requestor.
(request-wserver request) - reader - the wserver object describing the web server taking this request
(request-raw-request request) - reader - a string holding the exact request made by the client
(request-reply-code request) - accessor - the value describes the response code and string we will return for this request. See the value of the argument response in with-http-response for more information.
(request-reply-date request) - accessor - the date the response will be made (in Lisp's universal time format). This defaults to the time when the request arrived.
(request-reply-headers request) - accessor - an alist of some of the headers to send out with the reply (other headers values are stored in specific slots of the request object). Each entry in the alist is a cons where the car is a keyword symbol holding the header name and the cdr is the value (it is printed using the ~a format directive). Typically request-reply-headers isn't used, instead the headers to be sent are passed as the :header argument to with-http-body, or (setf reply-header-slot-value) is called.
(request-reply-content-length request) - accessor - the value to send as the Content-Length of this response. This is computed automatically by AllegroServe and thus a user program shouldn't have to set this slot under normal circumstances.
(request-reply-plist request) - accessor - this slot holds a property list on which AllegroServe uses to store less important information. The user program can use it as well.
(request-reply-strategy request) - accessor - the strategy is a list of symbols which describe how AllegroServe will build a response stream and will send back a response. More details will be given about the possible strategies at a future time.
(request-reply-stream request) - accessor - This is the stream to be used in user code to send back the body of the response. This stream must be used instead of the value of request-socket.
The Common Gateway Interface (CGI) specification allows web servers to run programs in response to http requests and to send the results of the execution of those programs back the web client. The CGI programs finds information about the request in its environment variables and, in the case of a put or post request, the body of the request is sent to standard input of the program.
CGI is a clumsy and slow protocol for extending the behavior of a web server and is falling out of favor. However there are legacy CGI applications you may need to call from AllegroServe. You invoke an external program using the CGI protocol with the run-cgi-program function.
auth-type timeout error-output env terminate)
In response to an http request, this runs program
which must be a
string naming an exectuable program or script followed optionally by
arguments to pass to that program. Before the program is
argument is how long AllegroServe should wait for a response from the program
giving up. The default is 200 seconds. The error-output
specifies what should be done with data the cgi program sends to its
This is described in detail below. The other keyword
arguments allow the
caller to specify values for the CGI environment variables that can't
automatically. path-info specifies the
variable, and similarly for path-translated, script-name,
and auth-type. If query-string
given and the uri that invoked this request contains
a query part then
that query part is passed in the QUERY_STRING environment
variable. If script-name
is not given then its value defaults to the path of the uri of the
you wish to add or modify the environment variables set for the cgi
process you can
specify a value for env. The value of env
be a list of conses, the car of each cons containing the environment
variable name (a
string) and the cdr of each cons containing the environment variable
string). env is checked after all the
variables are computed and the value given in env
will override the value
computed automatically. On Unix if terminate is true then after the cgi
program finishes responding (or the timeout period expires) the cgi
program will be forceably killed (first with SIGTERM and then SIGKILL)
if remains alive.
cgi programs send their result to standard output (file descriptor 1 on Unix). If they encounter problems they often send informative messages to standard error (file descriptor 2 on Unix). The error-output argument to run-cgi-program allows the caller to specify what happens to data sent to standard error. The possibile values for error-output are:
|nil||The cgi program's standard error is made the same as the Lisp process' standard error. This standard error may not be the same as the current binding of *standard-error*.|
|pathname or string||A file with the given name is opened and standard error is directed to that file.|
|:output||Standard error is directed to the same place as standard output thus the error messages will be mixed into the result of running the cgi program.|
|symbol or function||The function is run whenever there is data available to be read from standard error. It must read that data. It must return a true value if it detected an end of file during the read and nil otherwise. The function takes arguments: req ent stream|
A typical way of publishing a CGI page is this:
(publish :path "/cgi/myprog"
:function #'(lambda (req ent)
(run-cgi-program req ent "/server/cgi-bin/myprog")))
If you're concerned about capturing the error output then here's an example where we supply a function to collect all the error output into a string. Once collected we simply print it out here but in a real web server you would want to store it in a log file.
(defun cgierr (req ent)
(let ((error-buffer (make-array 10
#'(lambda (req ent stream)
(declare (ignore req ent))
(let ((ch (read-char-no-hang stream nil :eof)))
(if* (null ch) then (return))
(if* (eq :eof ch)
then (setq eof t)
(vector-push-extend ch error-buffer)))
(format t "error buffer is ~s~%" error-buffer)
Note: The ability to run CGI programs from AllegroServe was due to features added in Allegro Common Lisp version 6.1. This will not work in earlier versions of Allegro CL.
Forms are used on web pages in order to allow the user to send information to the web server. A form consists of a number of objects, such as text fields, file fields, check boxes and radio buttons. Each field has a name. When the user takes a certain action, the form data is encoded and sent to the web server. There are three ways that data can be sent to the web server. The method used is determined by the attributes of the <form> tag that defines the form
If you create a form with <form method="post" enctype="multipart/form-data"> then your url handler must do the following to retrieve the value of each field in the form:
It's important to retrieve all of the data sent with the form, even if that data is just ignored. This is because there may be another http request following this one and it's important to advance to the beginning of that request so that it is properly recognized.
Details on the functions are given next.
This returns nil or the MIME headers for the next form field in alist form. If nil is returned then there is no more form data. See parse-multipart-header for a simple way to extract information from the header.
For an input field such as <input type="text" name="textthing"> the value returned by get-multipart-header would be
(:param "form-data" ("name" . "textthing"))))
For an input field such as <input type="file" name="thefile"> the value returned by get-multipart-header would be something like
(:param "form-data" ("name" . "thefile")
("filename" . "C://down//550mhz.gif")))
Note that the filename is expressed in the syntax of the operating system on which the web browser is running. This syntax may or may not make sense to the Lisp pathname functions of the AllegroServe web server as it may be running on a totally different operating system.
This takes the value of get-multipart-header and returns values that describe the important information in the header.
The first value returned is
(get-multipart-sequence request buffer &key start end external-format)
This retrieves the next chunk of data for the current form field and stores it in buffer. If start is given then it specifies the index in the buffer at which to begin storing the data. If end is given then it specifies the index just after the last index in which to store data.
The return value is nil if there is no more data to return, otherwise it is the index one after the last index filled with data in buffer.
The buffer can be a one dimensional array of character or of (unsigned-byte 8). For the most efficient transfer of data from the browser to AllegroServe, the program should use a 4096 byte (unsigned-byte 8) array.
If the buffer is a character array then the data is converted from get-multipart-sequence's (unsigned-byte 8) array to characters using the given external-format (which defaults to the value of *default-aserve-external-format*).
get-multipart-sequence may return before filling up the whole buffer, so the program should be sure to make use of the index returned by get-multipart-sequence.
(get-all-multipart-data request &key type size external-format limit)
This retrieves the complete data object following the last multipart header. It returns it as a lisp object. If type is :text (the default) then the result is returned as a lisp string. If type is :binary then the result is returned as an array of element-type (unsigned-byte 8). size (which defaults to 4096) is the size of the internal buffers used by this function to retrieve the data. You usually won't need to specify a value for this but but if you know the values retrieved are either very small or very large it may make the operation run faster to specify an appropriate size. external-format is used when type is :text to convert the octet stream into characters. It defaults to the value of *default-aserve-external-format*. limit can be given an integer value that specifies the maximum size of data you're willing to retrieve. By default there is no limit. This can be dangerous as a user may try to upload a huge data file which will take up so much Lisp heap space that it takes down the server. If a limit is given and that limit is reached, get-all-multipart-data will continue to read the data from the client until it reaches the end of the data, however it will not save it and will return the symbol :limit to indicate that the data being sent to the sever exceeded the limit. It will return a second value which is the size of the data the client tried to upload to the server. If your application intends to handle very large amounts of data being uploaded to the server you would be better off using get-multipart-sequence since with that you can write the data buffer by buffer to the disk instead of storing it in the Lisp heap.
In AllegroServe the information sent to the web server as a result of filling out a form is called a query. We store a query as a list of conses, where the car of the cons is the name (a string) and the cdr of the cons is the value (another string). When a query is transmitted by the web browser to AllegroServe it is sent as string using the encoding application/x-www-form-urlencoded. We provide the following functions to convert between the encoding and the query list:
(form-urlencoded-to-query string &key external-format)
Decodes the string and returns the query list. The default value for external-format is the value of *default-aserve-external-format*.
(query-to-form-urlencoded query &key external-format)
Encodes the query and returns a string. The default value for external-format is the value of *default-aserve-external-format*.
user(4): (query-to-form-urlencoded '(("first name" . "joe")
("last name" . "smith")))
user(5): (form-urlencoded-to-query "first+name=joe&last+name=smith")
(("first name" . "joe") ("last name" . "smith"))
`(("last name" . ,(coerce '(#\hiragana_letter_ta
`(("last name" . ,(coerce '(#\hiragana_letter_ta
(assoc "last name"
(#\hiragana_letter_ta #\hiragana_letter_na #\hiragana_letter_ka)
You may want to restrict certain entities to be accessible from only certain machines or people. You can put the test for authorization in the entity response function using one of the following functions, or you can have the check done automatically by storing a list of authorizer objects in the entity.
These two functions invoke and process the Basic Authorization Method defined by the http specification. The password-authorizer class described below make use of these functions.
This function retrieves the Basic authorization information associated with this request, if any. The two returned values are the name and password, both strings. If there is no Basic authorization information with this request, nil is returned.
(set-basic-authorization request realm)
This adds a header line that requests Basic authorization in the given realm (a string). This should be called between with-http-response and with-http-body and only for response of type 401 (i.e. *response-unauthorized*). The realm is an identifier, unique on this site, for the set of pages for which access should be authorized by a certain name and password.
This example manually tests for basic authorization where the name is foo and the password is bar.
(publish :path "/secret"
#'(lambda (req ent)
(multiple-value-bind (name password) (get-basic-authorization req)
(if* (and (equal name "foo") (equal password "bar"))
then (with-http-response (req ent)
(with-http-body (req ent)
(html (:head (:title "Secret page"))
(:body "You made it to the secret page"))))
else ; this will cause browser to put up a name/password dialog
(with-http-response (req ent :response *response-unauthorized*)
(set-basic-authorization req "secretserver")
(with-http-body (req ent)))))))
The authorizer slot of an entity object can contain a authorizer object or a list of zero or more authorizer objects. When a request arrives for this entity the authorizer objects are consulted to see if this request should be permitted. In order for the request to be permitted, all authorizer objects must permit the request. AllegroServe supplies three interesting subclasses of authorizer and users are free to add their own subclasses to support their own authorization needs.
The protocol followed during authorization is this:
This subclass of authorizer is useful if you want to protect an entity using the Basic authorization scheme that asks for a name and a password. When you create this class of object you should supply values for the two slots:
|allowed||:allowed||list of conses, each cons having the form ("name" . "password") where any of the listed name password pairs will allow access to this page.|
|realm||:realm||A string which names the protection space for the given name and password. The realm will appear in the dialog box the browser displays when asking for a name and password.|
An example of its use is the following where we allow access only if the user enters a name of joe and a password of eoj or a name of fred and a password of derf.
(publish :path "/foo"
:authorizer (make-instance 'password-authorizer
:allowed '(("joe" . "eoj")
("fred" . "derf"))
#'(lambda (req ent)
(with-http-response (req ent)
(with-http-body (req ent)
(html (:head (:title "Secret page"))
(:body "You made it to the secret page"))))))
This authorizer class checks the IP address of the request to see if it is permitted access to the entity. The authorizer can specify a sequence of patterns and for each pattern a command of :accept (permit the access) or :deny (forbid the access). The first pattern that matches determines if the request is accepted or denied. If the pattern list is empty or if no pattern matches, then the request is accepted.
The single slot of an object of class location-authorizer is
|patterns||:patterns||a list of patterns and commands, where the syntax of a pattern-command is described below.|
A pattern can be
The example of using a location-authorizer only permits connections coming in via the loopback network (which occurs if you specify http://localhost/whatever) or if they come from one particular machine (tiger.franz.com). Note that we end the pattern list with :deny so that anything not matching the preceding patterns will be denied.
(publish :path "/local-secret-auth"
:authorizer (make-instance 'location-authorizer
:patterns '((:accept "127.0" 8)
#'(lambda (req ent)
(with-http-response (req ent)
(with-http-body (req ent)
(html (:head (:title "Secret page"))
(:body (:b "Congratulations. ")
"You made it to the secret page"))))))
This authorizer contains a function provided by the user which is used to test if the request is authorized. The function take three arguments, the http-request object, the entity and the authorizer object. It must return one of the four values that the authorize function returns, namely t, nil :deny or :done.
A function-authorizer is created as follows
:function #'(lambda (req ent auth)
t ; always authorize
The function slot can be set using (setf function-authorizer-function) if you wish to change it after the authorizer has been created.
Cookies are name value pairs that a web server can direct a web browser to save and then pass back to the web server under certain circumstances. Some users configure their web browsers to reject cookies, thus you are advised against building a site that depends on cookies to work.
Each cookie has these components:
(set-cookie-header request &key name value expires domain path secure http-only encode-value external-format)
This function must be called before with-http-body. It can be called more than once. Each call will cause one Set-Cookie directive to be sent to the web browser. The name and value arguments should be given (and they should be strings). They will be automatically encoded using the same encoding used in urls (we call it uriencoding). The purpose of this encoding is to convert characters that are either unprintable or those that have a special meaning into a printable string. The web browser doesn't care about the name and value, it just stores them and sends them back to the web server. If you use the get-cookie-values function to retrieve the cookie name and value pairs, then it will automatically decode the uriencoding.
You can disable the encoding of the value by specifying a nil
encode-value. This should only be
necessary if you are
working with buggy http client applications.
If the path argument isn't given, it will default to "/" which will allow this cookie to match all requests.
If the domain argument isn't given then it will default to the host to which this request was sent. If you wish to specify this you are only allowed to specify a subsequence of the host to which this request was sent (i.e the name of the machine running the webserver). The domain should have at least two periods in it (i.e. ".foo.com").
expires can be a lisp universal time or it can be the symbol :never meaning this should never expire. If expires isn't given or is nil then this cookie will expire when the user quits their web browser.
secure should be true or false. Any non-nil value is interpreted as true. The default value is false.
http-only should be true or false. Any non-nil value is interpreted as true. The default value is false.
The external-format is used to convert bytes to characters. It defaults to the value of *default-aserve-external-format*.
(get-cookie-values request &key external-format)
Return the cookie name and value pairs from the header of the request. Each name value pair will be in a cons whose car is the name and whose cdr is the value. The names and values will be decoded (in other words the decoding done by set-cookie-header will be undone). The external-format is used to convert bytes to characters. It defaults to the value of *default-aserve-external-format*.
These special variables contain information about AllegroServe or help control AllegroServe:
*aserve-version* - a list of three values: (major-version minor-version sub-minor-version) which is usually printed with periods separating the values (i.e. X.Y.Z).
*default-aserve-external-format* - a symbol or external format object which is the default value for those AllegroServe functions that take an external-format argument. http requests are normally run in separate lisp threads and those threads bind *default-aserve-external-format* to the value of the external-format argument to the start function. Thus changing the value of *default-aserve-external-format* in one thread will not affect its value in other threads. You should decide the default external format before you start AllegroServe running.
*http-response-timeout* - the default value for the timeout argument to with-http-response. [in future versions of AllegroServe we'll treat this value like *default-aserve-external-format* and bind it in each worker thread]
*mime-types* - a hash table where the keys are the file types (e.g. "jpg") and the values are the MIME types (e.g. "image/jpeg").
We'll describe here the steps AllegroServe goes through from the time it receives a request until a response to that request has been sent back to the browser. We want the protocol to be open so that users can extend AllegroServe's behavior to suit their needs. However given that AllegroServe is a new program and will be undergoing extensive review from its users, we expect that the protocol will change. It shouldn't lose any of its current extensibility but the names and argument lists of generic functions may change.
When a client connects to the port on which AllegroServe is listening, AllegroServe passes that connected socket to a free worker thread which then wakes up and calls the internal function net.aserve::process-connection. If there are no free worker threads then AllegroServe waits for one to be available.
In each worker thread the variable *wserver* is bound to the wserver object that holds all the information about the webserver on which the connection was made (remember that one AllegroServe process can be running more than one webserver). process-connection reads the request from the socket (but doesn't read past the header lines). If the request can't be read within *read-request-timeout* seconds (currently 20) then the request is rejected. The request is stored in an object of class http-request. Next process-connection calls handle-request to do all the work of the request and then log-request to log the action of the request. Finally if the response to the request indicated that the connection was to be kept open rather than being closed after the response, then process-connection loops back to the top to read the next request.
(handle-request (req http-request)) [generic function]
This generic function must locate the entity to handle this request and then cause it to respond to the request. If there is no matching entity then handle-request must send a response back to the client itself. handle-request uses locators to find the entity (more on this below), and then if an entity is found and that entity has an authorizer, it calls authorize to see if this request is allowed to access the selected entity. If the entity passes the authorization then process-entity is called to cause the entity to respond to the request. process-entity returns true if it processed the entity, and nil if did not in which case the search continues for an entity. If there is no entity to respond then failed-request is called to send back a failure message.
A locator is an object used to map requests into entities. The value of (wserver-locators *wserver*) is a list of locator objects. handle-request calls
(standard-locator (req http-request) (loc locator)) [generic function]
on each successive locator in that list until one returns an entity object. AllegroServe has two built-in locator classes, locator-exact and locator-prefix, that are subclasses of locator. When you call publish or publish-file you are adding the entity to locator of class locator-exact found in the wserver-locators list. When you call publish-directory you are adding to the locator of class locator-prefix. Users are free to define new locator classes. Locators should define the standard-locator method as well as
(unpublish-locator (loc locator)) [generic function]
which if called should remove all published entities from the locator.
Let's return to handle-request. It has called standard-locator and found an entity. Next it checks to see if the entity has an authorizer value and if so calls
(authorize (auth authorizer) (req http-request) (ent entity)) [generic function]
The return value will be one of
If there is no authorizer for this entity then we just call process-entity. If there is no entity, then we call failed-request.
(failed-request (req http-request)) [generic function]
send back a response to the effect that the url request doesn't exist on this server.
(denied-request (req http-request)) [generic function]
send back a response to the effect that access to the requested url was denied.
(process-entity (req http-request) (ent entity)) [generic function]
Send back a response appropriate to the given entity. The macros with-http-response and with-http-body should be used in the code that sends the response.
AllegroServe has a set of functions that perform http client-side actions. These functions are useful in generating computed pages that reflect the contents of other pages. We also use the client-side http functions to test AllegroServe.
The client-side functions described in this section are exported from the net.aserve.client package.
The function do-http-request sends a request and retrieves the whole response. This is the most convenient function to use to retrieve a web page.
If you need more control over the process you can use the functions: make-http-client-request, read-client-response-headers and client-request-read-sequence.
content content-type query format cookies
redirect redirect-methods basic-authorization
headers proxy proxy-basic-authorization
user-agent external-format ssl ssl-method
skip-body timeout compress keep-alive connection
certificate key certificate-password ca-file ca-directory verify max-depth)
Sends a request to uri and returns four values:
The uri can be a uri object or a string. The scheme of the uri must be nil or "http". The keyword arguments to do-http-request are
|method||:get||The type of request to make. Other possible values are :put, :post and :head. :head is useful if you just want to see if the link works without downloading the data.|
|protocol||:http/1.1||The other possible value is :http/1.0. Modern web servers will return the response body in chunks if told to use the :http/1.1 protocol. Buggy web servers may do chunking incorrectly (even Apache has bugs in this regard but we've worked around them). If you have trouble talking to a web server you should try specifying the :http/1.0 protocol to see if that works.|
|accept||"*/*"||A string listing of MIME types that are acceptable as a response to this request. The type listed can be simple such as "text/html" or more complex like "text/html, audio/*" The default is to accept anything which is expressed "*/*".|
|content||nil||If the method is :put or :post then the request should include something to be sent to the web server. The value of this argument is either a string, a vector of type (unsigned-byte 8) or an instance of a subclass of computed-content. It may also be a list of strings or vectors or instances of a subclass of computed-content. See the query argument for a more convenient way to :post data to a form.|
|content-type||nil||A string which is to be the value of the Content-Type header field, describing the format of the value of the content argument. This is only needed for :put and :post requests.|
|query||nil||This is a query alist of the form suitable for query-to-form-urlencoded. If the method is a :get then the value of this argument is urlencoded and made the query string of the uri being accessed. If the method is :post then the query string is urlencoded and made the content of the request. Also the content-type is set to application/x-www-form-urlencoded.|
|format||:text||The body of the response is returned as a string if the value is :text or as an array of type (unsigned-byte 8) if the value is :binary. When the body is a string the external-format argument is important.|
|cookies||nil||If you wish the request to include applicable cookies and for returned cookies to be saved, then a cookie-jar object should be passed as the value of this argument.|
|redirect||5||If the response is a redirect (code 301, 302, 303), and the method is one given by the value of redirect-methods then if this argument is true (and, if an integer, positive), do-http-request will call itself to access the page to which the redirection is pointed. If redirect is an integer then in the recursive call the value passed for redirect will be one less than the current value. This prevents infinite recursion due to redirection loops.|
|redirect-methods||(:get :head)||List of http methods which will be redirected if redirect is true.|
|basic-authorization||nil||If given, it is a cons whose car is the name and whose cdr is the password to be used to get authorization to access this page.|
||If given it is a digest-authorization object with
values in the username and password slots. The
digest-authorization object will be modified by do-http-request in
order to store the information needed to send as authorization
|headers||nil||an alist of conses (header-name
"header-value") for additional headers to send with the
request. The header-name should be a keyword symbol naming
the header, but it can be a string as well.
|proxy||nil||the name and optionally the port number of a proxying web server through which this request should be made. The form is of the argument is "www.machine.com" or "www.machine.com:8000" if the web server is listening on port 8000 rather than 80. Proxying web servers are often used when clients are behind firewalls that prevent direct access to the internet. Another use is to centralize the page cache for a group of clients.|
|no-proxy||nil||A list of strings naming the host names that will be directly accessed rather than going through a proxy. An entry in this list of "foo.com" will match any host name with "foo.com" as a suffix, such as "www.foo.com". If the value of no-proxy is a string then it is treated as if it were a list of that single string.|
||a cons of ("name" . "password")
used to authenticate this request to the proxy being used.
|user-agent||nil||If given it specifies the value of the User-Agent header to be sent with the request. Some sites respond differently based on the user-agent they believe has made the request. The lack of a User-Agent header may cause a server to ignore a request since it believes that it is being probed by a robot. The value of user-agent can be a string or one of the keywords :aserve, :netscape or :ie in which case an appropriate user agent string is sent.|
|external-format||the value of *default-aserve-external-format*||This determines the socket stream's external format.|
||If true then the client will
request that the server keep alive the connection. If the server
agrees then that socket connection is returned as the fifth value.
||If non nil then this is a socket
connected to the server for which this request is made. If the
socket is not valid (likely due to the server closing its end) then a
new socket will be created. Thus it is not an error.
|ssl||nil||If true then the connection is made using the Secure Sockets Layer protocol. If the uri uses the https scheme then ssl is assumed to be true and the ssl argument need not be specified. NOTE: if the underlying Lisp implementation supports it, Service Name Indication (SNI) will automatically be be used. do-http-request will use the :server-name keyword to acl-socket:make-ssl-client-stream, to indicate the hostname the client is attempting to connect to. This information is passed to the server to allow it to select the SSL certificate to present to the client.|
SSL/TLS for the use of this
|skip-body||nil||If the value is a fucntion (satisifies functionp) then the value is funcalled passing the client-request object as an argument. At this point the client-request object contains the information on the headers of the response. The function should return true if the body of the response should be skipped and nil returned as the first value from do-http-request. If skip-body is not a function and if its value is true then reading the body is skipped and nil returned in its place.|
||If given this is the number of
seconds this function will block waiting to connect to the server and
also to write or read to the socket
connected to the web server. If an I/O request blocks for
more than timeout seconds an error of class socket-error is signalled and the
on the error condition object will return :read-timeout or :write-timeout.
||If true then tell the server in
the request that we are able to accept a compressed body. If the
server decides to send a compressed body then the body will be
uncompressed by do-http-request before being returned to the caller.
ca-directory, verify, max-depth
||These values are passed as the
arguments to make-ssl-client-stream (documented in the ACL
documentation). Specifying these values is optional but it does
give you control of the client's SSL certificate management.
These values are used in a fully patched ACL 8.0 (or newer). In older versions of ACL they are ignored.
|cache||nil||A instance of class net.aserve.client:client-cache if you wish to consult and update this cache with this request. See the documentation on client-cache below.|
user(5): (do-http-request "https://franz.com")
<TITLE>Franz Inc: Allegro Common Lisp and Common Lisp Products</TITLE>
<BASE FONTFACE=\"helvetica, arial\" FONTSIZE=\"1\">
(("content-type" . "text/html") ("transfer-encoding" . "chunked")
("server" . "Apache/1.3.9 (Unix) PHP/3.0.14")
("date" . "Mon, 24 Apr 2000 11:00:51 GMT"))
It's easy to use do-http-request to fill in form objects on a page. If the form has input elements named width and height then you can send a request that specifies that information in this way:
:query '(("width" . 23) ("height" . 45)))
The above assumes that the method on the form is "GET". If the method is "POST" then a similar call will work:
(do-http-request "http://www.foo.com/myform.html" :method :post
:query '(("width" . 23) ("height" . 45)))
If the page uses digest authorization then you would call with arguments like
:digest-authorization (make-instance 'digest-authorization :username "joe" :password "secret"))
(get-content-length (cc my-computed-content-subclass))returns the number of bytes in the content.
(write-content (cc my-computed-content-subclass) stream)writes the bytes of the computed content to the stream.
(make-instance 'net.aserve.client:file-computed-content :filename "/a/b/myfile.txt")
Before we describe the lower level client request functions we will describe two classes of objects used in that interface.
Only :get and :head requests meeting certain criteria are cacheable: The request cannot have a query, basic or digest authentication, or new headers passed in.
You can specify the maximum size of the data in the cache by passing the :max-cache-size argument to make-instance of client-cache e.g.
(make-instance 'client-cache :max-cache-size 1000000)
When the number of bytes stored in the cache exceeds the max-cache-size plus *cache-size-slop* (default 100000) entries in the cache are removed so that the size is less than the maximum size minus *cache-size-slop*. The least recently used cache entries are removed first.
The caching code will strictly follow the HTTP caching specification
but you may wish to do more caching than would be permitted by
the specification. You may know for a fact that a certain url's
response can be cached for a certain period of time despite the
returned headers from that cache not indicating that fact.
There are two additional initargs to make-instance of client-cache
you can specify
If an HTTP response is returned with no caching headers and if the response code is one of the auto-cache-codes list then the response will be cached with an expiration date auto-cache-seconds in the future.
Both auto-cache-codes and auto-cache-seconds must be given or auto caching will not occur.
Accessors for the client-cache object (in the net.aserve.client package):
client-cache-max-cache-entry-size - if a response to be cached exceeds this number of bytes the response will not be cached (default 1,000,000 bytes).
client-cache-max-cache-size - when the cache size exceeds this value plus *cache-size-slop* the cache is automatically reduced in size.
client-cache-lookups - the number of times the cache was checked to see if it contained the uri passed to do-http-request.
client-cache-alive - the number of times the cache contains the desired response and the cache entry hadn't expired. In this case the response is returned from the cache.
client-cache-revalidate - the number of times the cache contains the desired uri but the cache entry had expired so the cache entry must be revalidated.
client-cache-validated - the number of times the cache contains the desired uri but the cache entry had expired so it was revalidated and found to be still valid.
(net.aserve.client:flush-client-cache cache &key expired all)Specify which entries in the cache should be removed immediately. Passing :all a true value will remove all entries. Passing :expired a true value will remove entries whose expiration date is in the past. Note that just because a cache entry has expired it doesn't mean it's worthless. When an expired entry is encountered AllegroServe will do a revalidation request which may return an indication that the entry is still valid thus saving the cost of returning the body of the request again. Also the cache entry will get a new expiration date.
net.aserve.client:*cache-size-slop* - specifies how many more bytes beyond the (client-cache-max-cache-size cache) value are permitted before the cache size is reduced to *cache-size-slop* less than the (client-cache-max-cache-size cache) value.
A client-request object includes the information about the request and the response.
The public fields of a client-request that are filled in after a call to make-http-client-request are:
|client-request-uri||uri object corresponding to this request|
|client-request-socket||socket object open to the web server denoted by the uri|
|client-request-cookies||the cookie-jar object (if any) passed in with this request.|
After read-client-response-headers is called, the following fields of the client-request objects are set:
|client-request-response-code||the integer that is the response code for this request. The most common codes are 200 for Success and 404 for Not Found.|
|client-request-headers||an alist of header values in the response. Each entry is a cons of the form ("header-name" . "header-value") or (:header-name . "header-value") for well known slots. The header names, if strings, are in all lower case.|
|client-request-protocol||A keyword symbol naming the protocol that the web server returned (which may be different that the protocol given in the request). A typical return value is :http/1.1|
|client-request-response-comment||A string giving a textual version of the response code. The string is arbitrary and you should not depend on all web servers returning the same string for any given response code.|
A cookie-jar is created with (make-instance 'cookie-jar).
returns an alist of the cookies in the jar where each item has the form:
(hostname cookie-item ...)
The hostname is a string which is matched against the suffix of the name of the host in the request (that is, a hostname of ".foo.com" matches "a.foo.com" and "b.foo.com". ). The hostname should have at least two periods in it. The following cookie-item objects in the list all apply to that hostname. A cookie-item is a defstruct object and has these fields
|cookie-item-path||A string that must be the prefix of the path of the request for it to match. The prefix "/" matches all paths.|
|cookie-item-name||The name of the cookie. A string.|
|cookie-item-value||The value of the cookie. A string.|
|cookie-item-expires||A string holding the time the cookie expires [in a future release we may make this a universal time]|
|cookie-item-secure||true if this cookie should only be sent over a secure connection.|
|cookie-item-http-only||true if this cookie should only be sent with the HttpOnly flag.|
uri &key method protocol keep-alive
accept cookies headers proxy proxy-basic-authorization
basic-authorization digest-authorization query
content content-type content-length
user-agent external-format ssl timeout)
This function connects to the web server indicated by the uri and sends the request. The arguments are the same as those for do-http-request and are documented there. There is one additional argument: content-length. This argument can be used to set the content-length header value in the request. After setting the content-length the caller of make-http-client-request would then be responsible for sending that many bytes of data to the socket to serve as the body of the request. If content-length is given, then a value for content should not be given.
If make-http-client-request succeeds in contacting the web server and sending a request, a client-request object is returned. If make-http-client-request fails, then an error is signalled.
The returned client-request object contains an open socket to a web server, thus you must ensure that client-request object isn't discarded before client-request-close is called on it to close the socket and reclaim that resource.
After calling make-http-client-request the program will send the body of the request (if any), and then it will call read-client-response-headers to partially read the web server's response to the request.
The default value for external-format is the value of *default-aserve-external-format*
This function reads the response code and response headers from the web server. After the function returns the program can use the client-request accessors noted above to read the web server's response. The body of the response (if any) has not been read at this point. You should use client-request-read-sequence to read the body of the response part by part, or read-response-body to read it as a whole.
&key start end)
This fills the buffer with the body of the response from the web server. The buffer should either be a character array or an array of (unsigned-byte 8). If given, start specifies the index of the first element in the buffer in which to store, and end is one plus the index of the last element in which to store.
The return value is one plus the last index in the buffer filled by this function. The caller of the function must be prepared for having the buffer only partially filled. If the return value is zero then it indicates an End of File condition.
(read-response-body client-request &key format
Should only be called after read-client-response-headers has been called. Reads the whole response body (if any) and returns it. If the format parameter has a value of :text (the default) the body is returned as a string, if given :binary, it will be an array of (unsigned-byte 8) elements. When reading text, the external format given when creating the request is used to decode characters.
The client-request object returned by make-http-client-request is closed. This returns the resources used by this connection to the operating system.
Given a client-request object after read-client-response headers has been called on it, determine if digest authorization is being requested and if so compute the authorization values based on the username and password in the digest-authorization object. Returns true if Digest Authorization was requested by the server and if the authorization values were successfully computed.
Digest authorization is more difficult since the authorization key passed by the client is based on values passed by the server when it rejected the request. Thus you need to make the same request twice. The do-http-request function handles this retry automatically. If you need to use client-request-read-sequence to read the data then you will have to do the retry as well. This function demonstrates how you use the above functions to do the retry and then to retrieve the data:
(defun getpage ()
;; demonstrate how to add digest authorization to the
;; page retrieval loop that uses client-request-read-sequence
(let ((creq (make-http-client-request "http://www.secret.com/whatever.html")))
(if* (eq 401 (client-request-response-code creq))
then ; try digest authorization
(let ((da (make-instance 'digest-authorization
(if* (compute-digest-authorization creq da)
then ; successfully computed digest authorization
; end request
; and create a new one
(setq creq (make-http-client-request
(if* (not (eql 200 (client-request-response-code creq)))
then (error "get failed with code ~s"
(let ((buffer (make-array 2048 :element-type 'character)))
(let ((length (client-request-read-sequence buffer creq)))
(if* (zerop length)
(format t "got buffer of length ~s:~%~s~%" length
(subseq buffer 0 length))))
(uriencode-string string &key external-format)
Convert the string into a format that would be safe to use as a
component of a url.
In this conversion most printing characters are not
All non printing characters and printing characters that
could be confused
with characters that separate fields in a url are encoded a %xy where
xy is the
hexadecimal representation of the char-code of the
external-format defaults to the value of *default-aserve-external-format*.
AllegroServe can serve as an http proxy. What this means is that web clients can ask AllegroServe to fetch a URL for them. The two primary uses for a proxy server are (but see the warning below):
In order to run AllegroServe as a proxy server you should specify :proxy t in the arguments to the net.aserve:start function. With this specified AllegroServe will still act as a web server for pages on the machine on which AllegroServe is running. AllegroServe will act as a proxy for requests to other machines.
Each web browser has it's own way of specifying which proxy server it should use. For Netscape version 4 select the Edit menu, then Preferences... and then click on the plus sign to the left of Advanced. Then select Proxies and click on Manual Proxy Configuration and the click on View and specify the name of the machine running AllegroServe and the port number on which AllegroServe is listening. Then click OK on all the dialog boxes.
For Internet Explorer 5 select the Tools menu, and then Internet Options.. and then the Connections tab, and then LAN Settings. Click on Use a Proxy Server and then click on Advanced and specify the machine name and port number for AllegroServe. Then click on OK to dismiss the dialog windows.
Warning: if you specify :proxy t to net.aserve:start, AllegroServe will proxy any http request on behalf of any browser that can access the server. This is known as an open proxy and this is a service which might be abused if accessible to strangers. This danger can be mitigated with proxy-control objects, described next.
In order to control who gets to use the proxy and what sites AllegroServe will proxy, you can pass a proxy-control object as the value of the :proxy argument instead of t.
The proxy-control object has two fields:
Values for either or both of the fields can be specified. An unspecified field means "allow everything"
location: The location slot is set with the :location initarg or with the proxy-control-location accessor. The value of the location field is nil or a location-authorizer object described in detail in another part of this document.
destinations: this slot is set with the :destinations initarg or the proxy-control-destinations accessor. The value can be:
Strings should be the names of the host to which proxying is allowed. It will be compared in a case insensitive way to the host part of the URI in the proxy request. Just specifying a hostname allows proxying to a server running on any port of that host.
Lists should be of the form (hostname port1 port2 ..) where the portN are integers. This allows access to servers running on only those ports of the host. Example: ("internal.franz.com" 80 8080) allows proxying to ports 80 and 8080 on internal.franz.com. If no ports are specified in the list format, e.g. ("www.franz.com"), then no ports are opened and the effect is the same (when destinations is non-nil) as not listing that hostname at all.
Proxy requests which do not specify any ports, e.g. ("http://internal.franz.com/blah/blah"), are interpreted as requesting port 80.
The host specified in a proxy request must match exactly (except that case is ignored). Thus specifying "franz.com" will only match requests for "franz.com" and not "www.franz.com"
(net.aserve:start :proxy (make-instance 'proxy-control :location (make-instance 'location-authorizer :patterns '((:accept "127.1") (:accept "192.168.1.0" 24) :deny)) :destinations '("www.cnn.com" "edition.cnn.com" "svcs.cnn.com" "ads.cnn.com")))
The proxy will accept connections from localhost (which is always IP address 127.1) and it will accept any IP in the range 192.168.1.0 to 192.168.1.255 which is presumably the local network on which the machine is located.
The proxy will only accept proxy requests that begin "http://www.cnn.com/", "http://edition.cnn.com/", etc.
If the list of allowed sites to proxy is large it's best to use a hash table to store them:
(setq ht (make-hash-table :test #'equalp)) (dolist (site '("www.cnn.com" "edition.cnn.com" "svcs.cnn.com" "ads.cnn.com" ("i.cdn.turner.com" 80 8000 9300) "i2.cdn.turner.com" )) (setf (gethash (if* (consp site) then (car site) else site) ht) (if* (consp site) then (cdr site) else t))) ;; followed by (make-instance 'proxy-control :destinations ht)
You can alter the proxy-control object while AllegoServe is running in order to change the authorization of the proxy.
authorize-proxy-request ((req http-request) (ent entity) (pc proxy-contol))
authorize-proxy-request ((req http-request) (ent entity) (pc (eql nil)))
For each HTTP request that has the form of a proxy request the generic function authorize-proxy-request is called, passing the request and entity objects and the value of (wserver-proxy-control wserver).
(wserver-proxy-control wserver) is set to the value of the :proxy argument to net.aserve:start if that value is of type proxy-control, otherwise it is set to nil. There are two primary methods, one for pc being a proxy-control and one for pc being nil. TThe first uses the location and description slots of the proxy-control object as described above to return true if proxying is authorized.
The second simply returns true since without a proxy-control object all proxying is permitted.
The AllegroServe cache is a facilty in development. We'll describe here the current status of the code.
The cache consists of a memory cache and a set of zero or more disk caches. Items initially live in the memory cache and are moved to the disk caches when the memory cache fills up. Items enter the memory cache due to a page being accessed via the proxy server. Items in the disk cache move back to the memory cache if the data portion must be sent back to the requesting client (some requests can be answered without sending back the contents of the page and for these the item stays in the disk cache).
You specify the sizes of each cache. The disk caches will never grow beyond the size you specified but the memory cache can exceed the specified size for a short time. A background thread moves items from the memory cache to the disk caches and we will allow you to control how often that thread wakes up and ensures that the memory cache is within the desired constraints.
When net.aserve:start is called you specify if you want caching and if so what size caches you want. A sample argument pair passed to net.aserve:start is
:cache '(:memory 10000000 :disk ("/tmp/mycache" 30000000) :disk (nil 20000000))
This says that the memory cache should be 10,000,000 bytes and that there should be two disk caches. One disk cache is the file "/tmp/mycache" and can grow to 30,000,000 bytes and the other cache will have a name chosen by AllegroServe and it can grow to 20,000,000 bytes. We should note here that one thing that distinguishes the AllegroServe caching facilty from that found in many other http proxy-caches is that AllegroServe uses a few large cache files rather than storing each cached item in a separate file in the filesystem.
A few other ways of specifying caching at startup is:
This will create a memory case of the default size (currently 10 megabytes) and it will create no disk caches.
This will create a memory cache of 20,000,000 byte and no disk caches.
When caching is enabled we publish two links to pages showing cache information. This is useful during debugging and is likely to change in the future. The two pages are /cache-stats and /cache-entries.
After AllegroServe reads a request and before it checks the locators to find an entity to handle the request, AllegroServe runs the request through a set of filters.
A filter is a function of one argument: the http-request object. The filter examines and possibily alters the request object. The idea is that filters can do large scale and simple url rewriting, such as changing all requests for one machine to another machine. The filtering occurs before the test to see if this is a proxy request so a filter can change a proxy request to a non proxy request or vice versa.
The currently active filters are found in two places. First the vhost-filters function of the applicable vhost returns a set of vhost specific filters. Next the wserver-filters function on the current wserver object returns a set of server global filters. Both of these functions are setf'able to change the set of filters.
A filter function returns :done if no more filters should be run after this one. If the filter returns anything else then subsequent filters in the list are run as well. If a filter in the vhost list returns :done then the server global filters are not even checked.
When a filter function runs it's most likely going to be looking at two slots in the request object, which are accessed via these functions:
Also the value of (header-slot-value request :host) is important to check and possibly change.
If the browser is setup to access the internet directly then a
request from the user
will cause the request to be sent to the server at foo.bar.com port 23 and the request will have:
If the browser is setup to send all requests through a proxy at proxy.blop.com then a request for
will come to proxy.blop.com and will have a different raw uri:
If the filter wants to alter the destination of request it should ensure that the three values mentioned above are set appropriately for the destination. If the new destination is not served by the current Allegroserve wserver, then the filter will have to make sure to turn it into a proxy request (and this will only work if this AllegroServe was started with proxying enabled).
It is possible for a single web server to act like two or more indepenent web servers. This is known as virtual hosting. AllegroServe supports the ability to run any number of virtual hosts in a single instance of AllegroServe.
AllegroServe runs on a single machine and listens for requests on one port on one or more more IP addresses. When a request arrives there is usually a header line labelled Host whose value is the specific hostname typed into the browser by the user. Thus if hostnames www.foo.com and www.bar.com both point to the same machine then it's possible for the webserver on that machine to distinguish a request for http://www.foo.com from a request for http://www.bar.com by looking at the Host header.
In order to make AllegroServe easy to use you can ignore the virtual hosting facility until you plan to use it. As long as you don't specify a :host argument to any of the publish functions when adding content to your site, everything you publish will be visible from your web server no matter which hostname the web browser uses to access your site. If you decide you want to make use of virtual hosting, then read on.
In AllegroServe a virtual host is denoted by an instance of class vhost. The contents of a vhost object are:
|vhost-log-stream||Stream to which to write logging information on requests to this virtual host||:log-stream|
|vhost-error-stream||Stream to which AllegroServe sends informational and error messages that are generated during request processing.||:error-stream|
|vhost-names||A list of all the names for this virtual host.||:names|
|vhost-filters||list of filter functions||:filters|
The defaults values for the two streams in a vhost object is the wserver-log-stream from the server object.
Every instance of AllegroServe has a default vhost object that can be retrieved from the wserver object via the function wserver-default-vhost. If a request comes in for a virtual host that's not known, then it's assumed to be for the default virtual host.
There are two ways to create virtual hosts in AllegroServe: implicitly or explicitly. If a publish function is called with a :host value that names a host not known to be a virtual host then a vhost instance will be created automatically and stored in the wserver's hash table that maps names to vhost objects. This is implicit virtual host creation.
If you know ahead of time the virtual hosts you'll be serving then it's better to setup all the virtual hosts explicitly. You create a vhost instance with make-instance and you register each virtual host in the wserver-vhosts table using gethash. Following is an example of setting up a server to have two virtual hosts, one that responds to three names and one that responds to two names. Since we are using the default vhost to represent the first virtual host, this virtual host will also receive requests for names we haven't mentioned explicitly.
(defun setup-virtual-hosts (server)
(let ((vhost-table (wserver-vhosts server))
(foo-names '("localhost" "www.foo.com" "foo.com"))
(bar-names '("www.bar.com" "store.bar.com")))
(let ((default-vhost (wserver-default-vhost server)))
(setf (vhost-names default-vhost) foo-names)
(dolist (name foo-names)
(setf (gethash name vhost-table) default-vhost)))
(let ((bar-vhost (make-instance 'vhost :names bar-names)))
(dolist (name bar-names)
(setf (gethash name vhost-table) bar-vhost)))))
When a request comes in, AllegroServe will determine which vhost is the intended target and if none is found it will select the default vhost as the intended target. The vhost so determined will be stored in the http-request object in the slot accessed by request-vhost function.
We now are in a position to describe what values the :host argument to the publish functions can take on. The :host argument can be nil or one of:
If the value of the :host argument is nil, then its value is assumed to be :wild.
The value of the :host argument is converted into a list of one or more vhost objects and/or the symbol :wild. The meaning of a vhost is clear: it means that this entity will be visible on this virtual host. The meaning of :wild is that this entity will be visible on all virtual hosts, except it can be shadowed by an entity specified for a particular virtual host. Thus you could publish an entity for :path "/" and :host :wild and it will be used for all virtual hosts that don't specify an entity for :path "/". Note that when a request comes in and the search is done for an entity to match the request every step of the way we look first for a vhost specific handler and then a :wild handler It is not the case that we first do a complete search for a vhost specific handler and then restart the search this time looking for a :wild handler.
A web server is a program that provides resources to a client program connecting over the network. The resources a web server has to offer is limited and it's important that network problems or buggy clients don't cause those resources to be unavailable to new clients. AllegroServe uses timeouts to ensure that no client can hold a web server resource for more than a certain amount of time.
Three common ways for a resource to be held are
For AllegroServe running in Acl 6.0 or older timeouts are done this way:
net.aserve::*read-request-timeout* - number of seconds AllegroServe allows for the request line (the first line) and all following header lines. The default is 20 seconds.
net.aserve::*read-request-body-timeout* - number of seconds AllegroServe allows for the body of the request (if any) to be read. The default is 60 seconds.
(wserver-response-timeout wserver) - the number of seconds AllegroServe allows for an http request function to be run and finished sending back its response. The initial value for this slot of the wserver object is found in *http-response-timeout* which defaults to 120 seconds. You can alter this timeout value with the :timeout argument to with-http-response or by specifying a :timeout when publishing the entity.
In Acl 6.1 we added the capability of having each I/O operation to a socket stream time out. This means that we don't have to predict how long it should take to get a request or send a response. As long as we're making progress reading or writing we know that the client on the other end of the network connection is alive and well. We still need a timeout to handle case (3) above but we can allow a lot more time for the http response since we aren't using this timer to catch dead clients as well. Thus we have these timeout values:
(wserver-io-timeout wserver) - the number of seconds that AllegroServe will wait for any read or write operation to the socket to finish. The value is initialized to the value of *http-io-timeout* which defaults to 60 seconds.
(wserver-response-timeout wserver) - the number of seconds AllegroServe allows for an http request function to be run and finished sending back its response. The initial value for this slot of the wserver object is found in *http-response-timeout* which defaults to 300 seconds. You can alter this timeout value with the :timeout argument to with-http-response or by specifying a :timeout argument to the publish function creating the entity.
publish-directory and publish-file default their timeout argument in a way that makes sense based on whether the Lisp supports I/O timeouts. If I/O timeouts are supported then there is no reason to do a global timeout for the whole response if you're just sending back a file. Thus in this case the timeout argument defaults to a huge number.
The HTTP protocol allows the client to request an entity be returned by the server. The server can simply send that entity as is or the client and server an agree that an encoded version of the entity should be transported. The server does the encoding, the client does the decoding and the caller of the client gets what it expects and is totally unaware that the entity was encoded while being transported.
The encoding supported by AllegroServer is called gzip.
Gzip is a compression algorithm. A gziped text file
can be substantially smaller than the original. gzip
will not shink (and it may even grow) files that already compressed
such as image files (jpeg, gif, png), movie files (mp4, mov, avi). or
compressed archive file (zip, tar.gz, tgz).
The are two types of compression handled by AllegroServe
The function adds a process lock to stream's property list (under the indicator :lock) if no such lock is present. Then it returns the object stream.
The AllegroServe logging functions make use of the stream's lock to ensure that only one thread at a time write log information to the stream. If the logging functions find that a a log stream doesn't have a lock associated with it then the log information will still be written to the stream but under heavy load the log information from multiple threads will become intermixed.
(map-entities function locator)
When one of the publish functions is called entities are placed in locator objects. The locator objects are then checked when http requests come in to find the appropriate entity. map-entities will apply the given function of one argument to all the entities in the given locator. One common use of map-entities is to find entities that you no longer wish to be published. For that reason map-entities will remove the entity passed to the function if the function returns the keyword symbol :remove as its value.
(log-for-wserver wserver message format)
This is a method that is called by AllegroServe whenever it wants
to log something. The
wserver argument can be specialized
on for your own server class, in order to make log messages go to your
own log stream, formatted using your own logging conventions.
message will always be a string, and
can be one of
AllegroServe itself uses to distinguish between messages that get a
full date timestamp, and those that get only a time. Your custom
method can choose to ignore this if it doesn't support multiple levels
On Windows NT (and Windows 2000 and Windows XP) when you log off all the programs you are running are terminated. If you want to run AllegroServe on your machine after you log out you have to start it as a Windows Service. This is easy to do thanks to code contributed by Ahmon Dancy.
The first step is to download the ntservice code and documentation from the Franz opensource site. Read the documentation carefully especially as regards the different capabilities of the accounts under which you may choose to run AllegroServe.
You'll probably want to build an AllegroServe application that can run either normally or as a service,. You can run it normally to debug it and then start it as a service when you're satisfied that it works.
Following is an example of how this can be done. I've decided that if the /service argument is given on the command line when I start my application then I'll start my application as a service, otherwise I start it normally. Here is the restart-init-function (to generate-application) that I define:
(defun start-aserve-application ()
(flet ((start-application ()
(net.aserve:start :port 8020)
(loop (sleep 100000))))
(if* (member "/service" (sys:command-line-arguments) :test #'equalp)
then ; start as a service
else ; start as a normal app
I use (loop (sleep 100000)) to ensure that the restart-init-function never returns.
In order to register my application as a service to the operating system I call ntservice:create-service like this:
(ntservice:create-service "aservetest" "Aserve Test Service"
"c:\\acl62\\testservice\\testapp\\testapp.exe -- /service")
Note that I use "--" before the "/service". This is very important. The "--" separates the arguments used to start up the program from the arguments passed to the program itself. The call to ntservice:create-service is done only once and need not be done from within your application.
Once an application is registered as a service you can start it by going to the Control Panel, selecting Administrative Tools and then Services. Locate the service you just added, right click on it and select start. You can stop the service with a right click as well.
A character set is a collection of characters and a rule to encode them as a sequence of octets. The default character set for web protocols is Latin1 (also known as ISO 8859-1). The Latin1 character set represents nearly every character and punctuation needed for western European languages (which includes English).
If you want to work with characters outside the Latin1 set you'll want to use the International version of Allegro CL which represents characters internally by their 16-bit Unicode value. In this section we'll assume that you're using International Allegro CL.
What the web protocols refer to as charset (character set) Allegro CL refers to as an external-format. Allegro CL uses a different term since it always uses 16-bit Unicode to represent characters internally. 16 bit unicode can represent nearly all characters on the planet. It's only when those characters are read from or written to devices outside of Lisp that the actual encoding of those characters into octets matters. Thus the external-format specifies how characters are encoded and specifies which Unicode characters are part of the character set that the external-format defines. Attempts to write a Unicode character that's not part of the character set results in a question mark being written.
External-formats are also used in Allegro CL to do certain character to character transformations. In particular on the Windows platform external formats are used to convert the lisp end of line (a single #\newline character) to the #\return #\linefeed character that is standard on Windows. Thus an external format such as :utf-8 has a different effect on Windows than on Unix, and this is not desirable for web applications. The function call (crlf-base-ef :utf-8) returns an external format on Windows and on Unix that simply does the character encoding part of the external format, and thus this is the external format you would want to use in a web application.
When a web server returns a response to a client it sends back a response line, a header and optionally a body. The response line and header are always sent using a subset of the Latin1 character set (the subset corresponding the US ASCII character set). The body is sent using the full Latin1 character set, unless otherwise specified. To specify the character set of the body you add an extra parameter to the Content-Type header. Instead of specifying a content type of "text/html" you might specify "text/html; charset=iso-8859-2". This alerts the http client that it must interpret the octets comprising the body of the response according to the iso-8859-2 character set. This however is not enough to make AllegroServe encode the Unicode characters it's sending to the client using the approrpriate external format. You would have to do this:
(with-http-response (req ent)
(with-http-body (req ent :external-format (crlf-base-ef :iso8859-2))
... generate and write page here..
Note that the charset names and external format name are similar but not identical. Check here for the charset names and check here for the Allegro CL external format names.
In order to make it easier to specify external formats in AllegroServe you can specify a default external format when you start the server (with the :external-format argument to the start function). The variable *default-aserve-external-format* will then be bound to this external format in each of the threads that processes http requests. It's the value of *default-aserve-external-format* that is used as the default argument to the :external-format argument to with-http-body.
The default value of the :external-format argument to the start function, and thus the default value of *default-aserve-external-format*, is (crlf-base-ef :latin1-base). This means that regardless of the locale in which you run AllegroServe, AllegroServe will by default use the Latin1 character set, which is what is expected by web clients..
A very useful character set is utf-8 which is the whole Unicode character set and thus comprises all of the characters you can store inside Lisp. The corresponding Allegro CL external format is the value of (crlf-base-ef :utf-8). Specifying this character set allows you to write web pages that can use characters from nearly every language in the world (whether the web browser can find the glyphs to display all those characters is another matter).
The brower sends characters to the web server when the user enters data into a form and submits the form. The important thing to remember is that the browser will encode characters using the character set that was specified for the web page containing the form. If you fail to specify a charset when the page was given to the web browser then the web browser will decide on its own how to encode characters that aren't part of the default character set ( which is of course Latin1). The browser will not tell you which encoding it chose. Therefore if you ever plan on allowing non-Latin1 characters to be specified in your forms you'll want to specify a charset for the page containing the form.
You can specify the charset in the Content-Type field of the header that's sent with the page (as we described above) or you can put it in the page itself using a meta tag:
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
Retrieving form data in AllegroServe is done with the request-query function and that function takes an :external-format argument so you can specify how the form data can be decoded. If your form sends multipart data then you can use the :external-format argument to get-multipart-sequence to retrieve the form data and decode the data.
The AllegroServe test page has links to a few pages that show how international characters work with AllegroServe. One of these is the International Character Display page. This page shows what happens when the charset and external-format are set to different values and a page containing international characters is displayed. It demonstrates how it important it is that those two character set specifications be kept in sync, and it shows that utf-8 is most likely the best choice for a character set for your web pages.
Debugging entity handler functions is difficult since these are usually run on a separate lisp thread. Also AllegroServe catches errors in entity handler functions, thus preventing you from interactively diagnosing the problem.
You can put AllegroServe in a mode that makes debugging easier with the net.aserve::debug-on function. Note that this is not an exported function to emphasize the fact that you are working with the internals of AllegroServe.
(net.aserve::debug-on &rest debugging-features-to-enable)
We've classified the debugging features and given each a keyword symbol name. This function turns on those named features. If no arguments are given, then debug-on prints the list of debugging features and whether each is enabled.
(net.aserve::debug-off &rest debugging-features-to-disable)
This function turns off the given list of features.
The list of debug features are given below. We flag three of particular interest:
|:info||AllegroServe prints information at certain places while doing its processing.|
|:xmit||AllegroServe prints what it receives from and sends to the client. In some cases the body of a request or response will not be printed.|
|:notrap||When enabled, this prevents AllegroServe from catching errors in entity handler functions. If an error occurs and you're running in an evironment where background processes automatically create new windows (such as the emacs-lisp interface) then you'll be given a chance to :zoom the stack and diagnose the problem. Note that if a timeout has been established to limit the amount of time that a certain step is allowed (and this is done by default) then the interactive debugging session will be aborted when the timeout is reached.|
Here are all features showing their parent features. Turning on a parent feature enables the child features. Some features have multiple parents.
Note there are no :xmit-proxy-server-request-* categories, because at the time of reading the request it's not yet known whether it's the going to be proxied so these show up as :xmit-server-request-*.
:all The parent of all debug features. :notrap If set than errors in handlers cause a break loop to be entered. (parent categories: :all) :zoom-on-error If set then print a zoom to the vhost-error-stream when an error occurs in a handler. (parent categories: :all) :log Category of features that write some kind of log. (parent categories: :all) :xmit Category of features that log the traffic between clients, servers. (parent categories: :log) :info General information. (parent categories: :log) :client Category of features that log client communication. (parent categories: :all) :server Category of features that log server communication. (parent categories: :all) :proxy Category of features that log proxy communication. (parent categories: :all) :request Category of features that log requests. (parent categories: :all) :response Category of features that log responses. (parent categories: :all) :command Category of features that log http request commands. (parent categories: :all) :headers Category of features that log request/response headers. (parent categories: :all) :body Category of features that log request/response bodies. (parent categories: :all) :xmit-client-request-command If set then print the client request commands. (parent categories: :xmit, :client, :request, :command) :xmit-client-request-headers If set then print the client request headers. (parent categories: :xmit, :client, :request, :headers) :xmit-client-request-body If set then print the client request bodies. (parent categories: :xmit, :client, :request, :body) :xmit-client-response-headers If set then print the client response headers. (parent categories: :xmit, :client, :response, :headers) :xmit-client-response-body If set then print the client response bodies. (parent categories: :xmit, :client, :response, :body) :xmit-server-request-command If set then print the server request commands. (parent categories: :xmit, :server, :request, :command) :xmit-server-request-headers If set then print the server request headers. (parent categories: :xmit, :server, :request, :headers) :xmit-server-request-body If set then print the server request bodies. (parent categories: :xmit, :server, :request, :body) :xmit-server-response-headers If set then print the server response headers. (parent categories: :xmit, :server, :response, :headers) :xmit-server-response-body If set then print the server response bodies. (parent categories: :xmit, :server, :response, :body) :xmit-proxy-client-request-command If set then print the proxy request command sent to the real server. (parent categories: :xmit, :proxy, :client, :request, :command) :xmit-proxy-client-request-headers If set then print the proxy request headers sent to the real server. (parent categories: :xmit, :proxy, :client, :request, :headers) :xmit-proxy-client-request-body If set then print the proxy request bodies sent to the real server. (parent categories: :xmit, :proxy, :client, :request, :body) :xmit-proxy-client-response-headers If set then print the proxy response headers sent by the real server. (parent categories: :xmit, :proxy, :client, :response, :headers) :xmit-proxy-client-response-body If set then print the proxy response bodies sent by the real server. (parent categories: :xmit, :proxy, :client, :response, :body) :xmit-proxy-server-response-headers If set then print the proxy response headers sent to the client. (parent categories: :xmit, :proxy, :server, :response, :headers) :xmit-proxy-server-response-body If set then print the proxy response bodies sent by the client. (parent categories: :xmit, :proxy, :server, :response, :body)