| Allegro CL version 9.0 Unrevised from 8.2 to 9.0. 8.2 version | ||||||||
This document contains the following sections:
1.0 IntroductionURI stands for Universal Resource Identifier. For a description of URIs, see RFC3986 (which replaces the obsolete RFC2396), which can be found in several places such as the IETF web site (https://tools.ietf.org/html/rfc3986). The related URN syntax is described in RFC8141 (https://tools.ietf.org/html/rfc8141)
URIs are a superset in functionality and syntax to URLs (Universal Resource Locators) and URNs (Universal Resource Names).
In URL slang, the scheme is usually called the `protocol', but it is called scheme in RFC1738. A URL `host' corresponds to the URI `authority.' The URL slang `bookmark' or `anchor' is `fragment' in URI lingo.
The URI facility might not be in an Allegro CL image by
default. Evaluate (require :uri) to ensure the
facility is loaded (that form returns nil if
the URI module is already loaded).
Broadly, the URI facility creates a Lisp object that represents a URI, and provides setters and accessors to fields in the URI object. The URI object can also be interned, much like symbols in CL are. This document describes the facility and the related operators.
Aside from the obvious slots which are called out in the RFC, URIs also have a property list. With interning, this is another similarity between URIs and CL symbols.
Allegro CL used to process URIs according to RFE2396. Now RFC3986 is used. The change was made in an unpdate released in September, 2018. The change causes changes one important area:
(net.uri:merge-uris (net.uri:parse-uri "?bar")
(net.uri:parse-uri "http://example.com/foo"))
RETURNS #<uri http://example.com/foo?bar>
RATHER THAN #<uri http://example.com/?bar>
Other than that, there are new fields and accessors (such as the URN accessor urn-q-component, as called for in RFC8141).
The uri module, which can be loaded with (require :uri), contains both
the URI and the IRI functionality. Symbols naming objects (functions,
variables, etc.) in the
uri module are exported from the net.uri
package.
URIs are represented by CLOS objects. Their slots are:
scheme host port path query fragment plist ipv6 zone-id
The host and port slots together
correspond to the authority (see RFC3986). There is
an accessor-like function, uri-authority, that can be used to extract
the authority from a URI. See the RFC3986 specifications pointed to at
the beginning of the Section 1.0 Introduction for
details of all the slots except plist. The
plist slot contains a standard Common Lisp property
list.
All symbols are external in the net.uri package,
unless otherwise noted. Brief descriptions are given in this document,
with complete descriptions in the individual pages.
uri: the class of URI objects.
urn: the class of URN objects.
Arguments: object
Returns true if object is an instance of class
uri.
Arguments: uri &key place scheme host port path query fragment plist
Copies the specified URI object. See the description page for information on the keyword arguments.
uri-scheme
uri-host
uri-port
uri-path
uri-query
uri-fragment
uri-plist
uri-ipv6
uri-zone-id
Arguments: uri-object
These accessors return the value of the associated slots of the uri-object
Arguments: uri-object
Returns the authority of uri-object. The authority combines the host and port.
Arguments: uri stream
Print to stream the printed representation of uri. This operator is the inverse of parse-uri. This operator should not be applied to the output of string-to-uri.
Arguments: string &key (class (quote uri))
Parse string into a URI object. This operator is the inverse of render-uri. This operator should not be applied to the output of uri-to-string.
Arguments: uri
Convert uri to a string. This operator is the inverse of string-to-uri. This operator should not be applied to the output of render-uri.
Arguments: string
Parse string into a URI object if possible. Signal an error if not possible. This operator is the inverse of uri-to-string. This operator should not be applied to the output of render-uri. string-to-uri differs from parse-uri does in that it does not decode the query portion of the string while parse-uri does.
Arguments: uri base-uri &optional place
Return an absolute URI, based on uri, which can be relative, and base-uri which must be absolute.
Arguments: uri base
Converts uri into a relative URI using base as the base URI.
Arguments: uri
Return the parsed representation of the path.
Arguments: object
Defined methods: if argument is a uri object, return it; create a uri object if possible and return it, or error if not possible.
Arguments: pathname
Converts a pathname to a file scheme URI.
Arguments: uri
Converts a file scheme URI to a pathname.
urn-nid
urn-nss
urn-q-component
urn-r-component
urn-f-component
Arguments: urn-object
These accessors return the value of the associated slots of the urn-object
The variable *strict-parse* controls how strictly the
parser observes syntax rules (many websites violate these rules and so
will not parse when they are strictly
observed). *strict-parse* has initial
value t.
The method uri-path returns the path portion of the URI, in string form. The method uri-parsed-path returns the path portion of the URI, in list form. This list form is discussed below, after a discussion of decoding/encoding.
RFC2396 lays out a method for inserting into URIs reserved characters. You do this by escaping the character. An escaped character is defined like this:
escaped = "%" hex hex hex = digit | "A" | "B" | "C" | "D" | "E" | "F" | "a" | "b" | "c" | "d" | "e" | "f"
In addition, the RFC defines excluded characters:
"<" | ">" | "#" | "%" | <"> | "{" | "}" | "|" | "\" | "^" | "[" | "]" | "`"
The set of reserved characters are:
";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" | "$" | ","
with the following exceptions:
From the RFC, there are two important rules about escaping and unescaping (encoding and decoding):
The implication of this is that to decode the URI, it must be in a parsed state. That is, you can't convert %2f (the escaped form of "/") until the path has been parsed into its component parts. Another important desire is for the application viewing the component parts to see the decoded values of the components. For example, consider:
https://franz.com/calculator/3%2f2
This might be the implementation of a calculator, and how someone would execute 3/2. Clearly, the application that implements this would want to see path components of "calculator" and "3/2". "3%2f2" would not be useful to the calculator application.
For the reasons given above, a parsed version of the path is available and has the following form:
([:absolute | :relative] component1 [component2...])
where components are:
element | (element param1 [param2 ...])
and element is a path element, and the param's are path element parameters. For example, the result of
(uri-parsed-path (parse-uri "foo;10/bar:x;y;z/baz.htm"))
is
(:relative ("foo" "10") ("bar:x" "y" "z") "baz.htm")
There is a certain amount of canonicalization that occurs when parsing:
(:absolute) or
(:absolute "") is equivalent to a
nil path. That is,
http://a/
is parsed with a nil path and
printed as http://a. "foob%61r" is parsed into
"foobar"
and appears as "foobar"
when the URI is printed.
The variable *strict-parse* controls how strictly the
parser observes syntax rules (many websites violate these rules and so
will not parse when they are strictly observed).
This section describes how to intern URIs. Interning is not mandatory. URIs can be used perfectly well without interning them.
Interned URIs in Allegro are like symbols. That is, a string representing a URI, when parsed and interned, will always yield an eq object. For example:
(eq (intern-uri "https://franz.com")
(intern-uri "https://franz.com"))
is always true. (Two strings with identical contents may or may not be eq in Common Lisp, note.)
The functions associated with interning are:
Arguments: &key size
Make a new hash-table object to contain interned URIs.
Arguments:
Return the object into which URIs are currently being interned.
Arguments: uri1 uri2
Returns true if uri1 and uri2 are equivalent.
Arguments: uri-name &optional uri-space
Intern the uri object specified in the uri-space specified. Methods exist for strings and uri objects.
Arguments: uri &optional uri-space
Unintern the uri object specified or all uri objects (in
uri-space if specified) if
uri is t.
Arguments: (var &optional uri-space result) &body body
Bind var to all currently defined uris (in uri-space if specified) and evaluate body.
(uri= (parse-uri "https://franz.com/") (parse-uri "https://franz.com"))
(eq (intern-uri "https://franz.com/")
(intern-uri "https://franz.com"))(eq (intern-uri "https://franz.com:80/foo/bar.htm")
(intern-uri "https://franz.com/foo/bar.htm"))#u"..." is shorthand for
(parse-uri "...") but if an existing
#u dispatch macro definition exists, it will
not be overridden.
user(10): (setq u #u"http://foo.bar.com/foo/bar") #<uri http://foo.bar.com/foo/bar> user(11): (setf (net.uri:uri-host u) "foo.com") "foo.com" user(12): u #<uri http://foo.com/foo/bar> user(13):
This allows URIs behavior to follow the principle of least surprise.
There are deviations from the grammar in the RFCs. The special
net.uri:*strict-parse* controls whether the
parser is RFC compliant. When net.uri:*strict-parse*
is nil, the parse will differ in these ways:
Both of these changes are necessary for parsing URIs available in the wild.
uri(10): (use-package :net.uri) t uri(11): (parse-uri "foo") #<uri foo> uri(12): #u"foo" #<uri foo> uri(13): (setq base (intern-uri "https://franz.com/foo/bar/")) #<uri https://franz.com/foo/bar/> uri(14): (merge-uris (parse-uri "foo.htm") base) #<uri https://franz.com/foo/bar/foo.htm> uri(15): (merge-uris (parse-uri "?foo") base) #<uri https://franz.com/foo/bar/?foo> uri(16): (setq base (intern-uri "https://franz.com/foo/bar/baz.htm")) #<uri https://franz.com/foo/bar/baz.htm> uri(17): (merge-uris (parse-uri "foo.htm") base) #<uri https://franz.com/foo/bar/baz.htm?foo.htm> uri(18): (merge-uris #u"?foo" base) #<uri https://franz.com/foo/bar/?foo> uri(19): (describe #u"https://franz.com") #<uri https://franz.com> is an instance of #<standard-class net.uri:uri>: The following slots have :instance allocation: (describe #u"https://franz.com") #<uri https://franz.com> is an instance of #<standard-class uri>: The following slots have :instance allocation: net.uri::scheme :http net.uri::userinfo nil net.uri::port nil net.uri::path nil net.uri::query nil net.uri::fragment nil net.uri::plist nil net.uri::.host "franz.com" net.uri::.ipv6 nil net.uri::.zone-id nil net.uri::escaped nil string "https://franz.com" net.uri::parsed-path nil net.uri::hashcode nil uri(20): #u"foobar#baz%23xxx" #<uri foobar#baz#xxx>
Copyright (c) 1998-2019, Franz Inc. Oakland, CA., USA. All rights reserved.
This page was not revised from the 8.2 page.
Created 2012.5.30.
| Allegro CL version 9.0 Unrevised from 8.2 to 9.0. 8.2 version | ||||||||