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These other tutorials also deal with AllegroServe:
AllegroServe is the opensource webserver written by Franz Inc. You can download and read documentation on AllegroServe at http://opensource.franz.com/aserve/.
This tutorial explains how to redirect an AllegroServe request to a different URI. It refers to portions of the HTTP 1.1 protocol as described in RFC2616. This tutorial assumes the user is familiar with form processing in AllegroServe. If you are not, you may find these additional AllegroServe tutorials to be of use: Tutorial on GET requests in AllegroServe and Tutorial on POST requests in AllegroServe.
An HTTP redirect describes a class of server responses (status code 3xx) that inform the client that some or all of the request should be accessed via a different URI, which is passed in the response to the client via the "Location" header.
NOTE: This tutorial is highly dependent on the extent to which client agents support the HTTP/1.1 protocol. It is expected that there should be similar behavior amongst modern HTTP/1.1 compliant browsers. In older browsers, your mileage may vary. The second example below, for example, makes use of the 303 status code. It is mentioned in the HTTP/1.1 spec that this code is not well supported in pre 1.1 client agents.
Below, we'll show how to send different response codes and modify response headers. First, let's get AllegroServe up and running. Follow the following three preliminary steps to get AllegroServe running and ready for the tutorial.
Start Allegro CL in the usual way. Once you have a prompt, enter the following form to load AllegroServe (it is not an error to enter that form if AllegroServe happens to already be loaded):
(require :aserve)
We define a package in which to define the code for this tutorial. The AllegroServe functionality we will be using is exported from the :net.aserve package, so our package will :use it. Since we will also be generating html, we must also use the :net.html.generator package. This package is defined by the htmlgen module, which is loaded as part of AllegroServe. Evaluate the following forms to define our package, which we are calling :demo, and make it the current package:
(defpackage :demo (:use :excl :cl :net.aserve :net.html.generator)) (in-package :demo)
Now let's get a server running. You will need to choose a port that is available and that the operating system will permit you to use. Web servers normally listen on port 80. On UNIX-like systems (macosx included) port 80 can only be allocated by the the superuser (called root). On windows any user can open port 80 as long as it's not yet allocated. In order to make this tutorial work on both Unix and Windows (and not require that you run as root on Unix), we'll put our web server on the localhost at port 8000. Evaluate the following form to start the server. (The function start is in the :net.aserve package. We do not need a package qualifier because we are in our :demo package which uses :net.aserve.
(start :port 8000)The webserver is now up and running, but we've provided it with no content to deliver to curious clients. If we visit http://localhost:8000/ right now, we'll get AllegroServe's standard "404 Error: Not found" response:
Not Found The request for http://localhost:8000/ was not found on this server. AllegroServe 1.2.43We will create some content next, as part of our discussion of redirects.
We create some content for a company StuffCo that has a webpage describing various types of "new stuff".
(defun new-stuff-entity-1 (req ent)
(with-http-response (req ent)
(with-http-body (req ent)
(html (:html (:head (:title "StuffCo, the leader in new stuff!"))
(:body (:h2 "Important new info on new stuff 1")
(:p "Here's the latest update on our new stuff 1.")))))))
(defun new-stuff-entity-2 (req ent)
(with-http-response (req ent)
(with-http-body (req ent)
(html (:html (:head (:title "StuffCo, the leader in new stuff!"))
(:body (:h2 "Great new info on new stuff 2")
(:p "Finally, new stuff 2 is here!")))))))
(publish :path "/new-1"
:content-type "text/html"
:function #'new-stuff-entity-1)
(publish :path "/new-2"
:content-type "text/html"
:function #'new-stuff-entity-2)
The web designers at StuffCo want users to be able to visit http://localhost:8000/new and always see info on the latest and greatest new stuff. We'll set up a redirect to accomplish this.
(defparameter *new-stuff-rel-uri* "new-1") (publish :path "/new" :content-type "text/html" :function #'(lambda (req ent) (with-http-response (req ent :response *response-found*) (setf (reply-header-slot-value req :location) (format nil "http://localhost:8000/~a" *new-stuff-rel-uri*)) (with-http-body (req ent) ;; empty body. must be called as this is what ;; actually pushes response out to client. ))))
Evaluate the above code in your lisp session and visit http://localhost:8000/new. You will be automatically redirected to http://localhost:8000/new-1. If you rebind *new-stuff-rel-uri* to "new-2" and revisit the page, you will see that AllegroServe now redirects you to http://localhost:8000/new-2.
The first thing of note in the function above is that we add ":response *response-found*" in the with-http-response wrapper. This tells AllegroServe how we want to respond to the incoming request. *response-found* is exported from the :net.aserve package and is a response struct containing the status code and a description of the code.