This file documents Guile-Web by Clinton Ebadi

Copyright 2003,2004,2005 Clinton Ebadi

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts.

This document describes Guile-Web by Clinton Ebadi

This document applies to version 0.5.1 of the library named Guile-Web

Copyright 2003,2004,2005 Clinton Ebadi

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts.

Introduction
************

Guile-web is a set of modules for Guile Scheme intended to make programming web applications in Guile easier. Guile-web is not intended to be used alone; rather as a supplement to guile-www (see Guile-WWW Manual (Guile-WWW)). Guile-web adds higher level concepts like session management to Scheme web programming.

Http Header Printing
********************

(web header) Module

A web application may need to manually output Http Headers. Guile-Web apps may be running as mod_lisp, fastcgi, or normal clients, and so must be able to output headers in different formats (e.g. mod_lisp uses KEY\nVALUE instead of KEY: VALUE). As such, all Guile-Web apps should use the (web header) module for outputting Http headers.

 -- Function: header:display port name value
     This displays the header NAME to PORT with VALUE. This can be overridden by a GOOPS method (indeed this is what mod_lisp does). The default implementation outputs headers in standard form NAME: VALUE\r\n.

Hash-Dash reader extension
**************************

(web hash-dash) Module

Scripts often time need to echo large amounts of static html. Doing this with Scheme display is extremely tedious, so guile-web provides the #- reader extension to do this. To use it you put a #- followed by as many lines of text as you want with a -# at the end of the text block. This reader extension will return the text block as a string. For example:

     ;;; output page header
     (define (header title)
     (for-each display
       (list
         #-
         <?xml version="1.0" encoding="utf-8"?>
         <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
             "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

         <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
           <head>
             <title>-# title #-</title>
           </head>
         -#))
     )
     (header "foobar")

That will create a xhtml 1.0 header.

Session Management
******************

(web session) Module

Session Management is a powerful tool that makes web programming much easier if you are doing authentication. I won't go into the details of what a session is here, look on Google for that (or send me an email telling me to put a blurb on it here if you really want it in the manual). You must call session:start before you output any other headers. You also must call session:save before you exit your script or else ALL changes to the session will be LOST.

  * session:start
     Call this before you make any output to start the session. If a previous session exists for the user, it will be restored, otherwise a new session is created. This returns #t if a new session is successfully created or the old one is restored and #f if something fails (e.g. headers have already been sent).

  * session:save
     Call this when you are finished with the session or when you wish to save the current session data. This will cause the current session data to be written out to disk. It can possibly be very time consuming (due to the design of the serializer)

  * session:destroy
     Call this when you want to destroy the session (e.g. the user logs out). All of the variables associated with the current session are destroyed. This returns #t if the session is successfuly destroyed and #f if something fails (e.g. a session doesn't currently exist).

  * session:set-save-path! path
     This sets the path where session data is saved. The default path is /tmp/. If you require secured sessions, you may want to run your scripts setuid as a special user and create a directory that only that user can read from to store your session data. This must be called before session:start.

  * session:set-cookie-name! name
     This sets the name of the cookie sent to the user to manage their session. You should only have to change this if you want to use more than one session cookie for a domain (e.g. you have multiple users using your domain for hosting). Of course, it is probably good to just set this to a more descriptive name than the default libcgi name anyway. before session:start.

  * session:register-var name value
     This registers name (which must be a symbol) with the current session and sets it's value to value. value is serialized using serialize from the object serialization module, see Object Serialization. Not all data types can be serialized; if a type is not supported you will have to write a serializer and deserializer for it. This returns #t if name is succesfully registered and #f on failure (e.g. name has already been registered).

  * session:unregister-var name
     This unregisters the session variable name. Returns #t if name is succesfully unregistered; #f otherwise (e.g. name is not a valid session variable).

  * session:alter-var! name new-value
     The session variable name is set to new-value. This return #t if name is succesfully set to new-value.

  * session:get-value name
     This gets and returns the value of the session variable name. This returns the value of name on success and "" on failure.

  * session:var-exists? name
     This checks if the session variable name exists. If it does, #t is returned; otherwise #f is returned.

An easy way to to ensure that the session is saved if you are using scripts that execute and exit is to add session:save to the exit-hook hook.

     (add-hook! exit-hook session:save)

Object Serialization
********************

(web serialize) Module

When you serialize an object you transform the object into a representation suitable for storing in a file (usually). The serialize module exports several functions for serializing and unserializing GOOPS objects. Note that every SMOB has a GOOPS class associated with it once GOOPS is loaded (?).

Note that this module is really meant for internal usage by the session mananger, but since you have to add your own serializers for user defined types, I figured I may as well may the entire API public (someone might find it useful).

  * Generic %serialize (item <type>) serial-table
     You should write a version of %serialize for every type you want to serialize, except for the built in types which already have serializers or any GOOPS class. Simply (define-method (%serialize (item <type>))) to create your new serializer. The serialize must produce a dotted pair in the form (type . value). E.g. a <number> is serialized as (<number> . value). type is the symbolic representation of the type. %serialize must return the serialized object as an sobject to the caller. This can be done by using object->sobject (e.g. (object->sobject (cons 'type value))). Note that the default GOOPS %serialize method may not do what you want it too. You can customize your object serialization like you would with any part of the standard GOOPS MOP. serial-table is used interally by other procedures that you may have to use.

  * @serialize item serial-table
     If your object is a container object, you must call @serialize on the items contained within your container. Simple call @serialize on each item, passing along the serial-table given to %serialize.

  * unserialize
     This will unserialize the serialized object serialized-data and return it.

  * add-unserializer type unserializer
     This adds an unserialize for type. The function unserializer takes two arguments which are the value member of the serialized data and the serial-table. E.g. take the serialized data "(<number> . 45)"; unserializer will be passed 45 and a hash table containing partially unserialized data as its argument. unserializer must return the unserialized object.

  * @unserialize item serial-table
     If your object is a container, just as you called @serialize on each member of the container during serialization, you must call @unserialize on each item.

Miscellaneous Database Tools
****************************

(web db) Module

These are only useful if you are using SimpleSQL, available from http://guile-simplesql.sourceforge.net/. (Maybe this module will be merged into it). The problem with simplesql is that it returns a list of vectors that is very difficult to use. This module defines a set of procedures that converts the result of a simplesql-query into a much nicer form. We will call this data type an assoc.

  * db:res->assoc result
     This converts the result of a simplesql-query into the form used by the module. This returns the new assoc.

  * db:numrows? assoc
     This returns the number of rows in assoc.

  * db:fetch-row assoc row-num
     This fetches the hash table at row-num in assoc.

  * db:get hash-table key
     This returns the data associated with the key key in the hash table hash-table. key is a symbol that is the name of the row in the query (e.g. the row named "foo" becomes the key 'foo).

If you would like to iterate over the result you can use array-for-each and array-map (or any of the other array functions) because a vector is simply an array of rank 1. I decided to use a vector instead of a list for this because it is more efficient for this (e.g. the result is constant, the number of rows may be very large and accessing a large numbered row is constant time for the vector and O(N) time for a list, etc.).

XHtml Generation
****************

(web xhtml) Module

Being able to generate correct HTML is a useful thing, so I have written a set of procedures for generating xhtml 1.0 documents. Note that correctness isn't entirely forced; you can, for example, put an inline element in a place where only a block level element is valid; but it does make generating a xhtml document somewhat easier.

There are two ways to use the html module: with the global instance or by specifying your own instance. If you use your own object, you must make a <html-document>, which takes these keyword arguments:

  * #:port The port to display output to

  * #:attributes Default attribute values for all tags

#:attributes is a list of lists that specify the default values for all tag attributes, e.g. ((style "special style") (class "magic")).

  * xhtml:print <DOCUMENT> EXPRESSION ...

To display data generated by the various tag procedures, you use xhtml:print. If the first argument is a <html-document> all of the tags will output using the default port for that object and use the default attribute values for that object as well. If the first argument is not a <html-document>, then the expressions will be printed to the output port of the global <html-document> which is the (current-output-port) of the dynamic root you are in (there is also one global <html-document> per dynamic root).

  * xhtml:tags TAGS ... If you need to use more than one tag where normally only one can be used, simply pass them all to xhtml:tags. This is useful if you wish to xhtml:print multiple tags which are on the same level in the document heirarchy as the others.

  * xhtml:TAGNAME <#:atts attributes> <contained tags>

  * xhtml:TAGNAME-start <#:atts attributes>

  * xhtml:TAGNAME-end

All tags have a producedure named xhtml:TAGNAME. If the tag is non-empty, this may tag any number of forms to be printed inside of the tag as arguments, including other tags. Also is the tag is non-empty, there are -start and -end procedures defined to spit out the start and end tags of the tag. If a tag is empty, it may not contain any other data. All tags take an optinal #:atts keyword argument that contains a list of lists that specify the attributes for the tag in the form ((attribute-name-as-a-symbol "attribute value in a string") ...). The start tag also supports this, the end tag doesn't. You must print the output of all the tag function with xhtml:print.

All documents should begin with a call to xhtml:dtd which returns the DTD for the document. Its #:atts argument takes one member: encoding which is the encoding of the document. This defaults to "iso-8859-1".

Available tags:

     [file xhtmldoc.texinfo not included]

An example:

     (use-modules (web html)
     	     (web hash-dash))

     (display "Content-Type: text/html\r\n\r\n")
     (force-output (current-output-port))

     (xhtml:print
      (xhtml:dtd
       (xhtml:html-start)))

     (xhtml:print
      (xhtml:head
       (xhtml:title "MOO")))

     (xhtml:print
      (xhtml:body-start)
      (xhtml:h1 "tra la la!")
      (xhtml:p
       #- Moo moo moooooooooo. I am so cool.
          Multiple lines are so great.
          All will fear my elite! -#
          (xhtml:br)
          #- This is where the second line begins. -#)
      (xhtml:body-end)
      (xhtml:html-end))

There is another procedure, xhtml:tag-tree->shtml TAG which accepts a tag as its argument and return the tag tree in shtml (a subset of SXML used by HtmlPrag).

Page Templates
**************

(web template) Module

Languages like PHP allow one to embed code within a document. The solution used by PHP isn't really optimal; guile-web uses a slightly better method of page templates. A page template is just a document with a bit of special formatting to make calls to various template procedures. This is somewhat similar to Perl's Mason module but is currently much more limited.

Scheme procedures:

  * template:parse COMMAND-TABLE PORT, reads from PORT and looks for template procedure calls. Procedures are supplied in COMMAND-TABLE which is a hash table of symbol and procedure pairs. template:parse returns a list of strings that represent non-template portions of the port along with any data returned by template calls. The list can then be processed however one chooses (e.g. a simple parse-and-display script could (for-each display (template:parse ...))). This will call template:error when an error occurs.

  * template:error FMT . ARGS, Whenever an error occurs, template:parse calls this procedure with a format string (FMT) usable by simple-format along with the ARGS to simple-format. Anything returned by this procedure will end up in the list returned by template:parse. By default this throws an error with the key 'web:format:error.

  * template:set-error-handler ERROR-HANDLER, use this to override the default template:error procedure. This returns the current error handling procedure.

To make a template call from a template, you encase the call in square brackets ([ and ]). The call is merely a procedure call that is expected to return some data that is substituted into the page at that point. If a double [[ is found it will be inserted into the output stream as a single [; a double ]] can be used inside of a template call to pass a literal ] to the procedure.

An example script that parses a page:

     ;;; page.scm
     (use-modules (web template))

     (let
       (
        ;; open template
        (my-file (open-input-file "page.tmpl"))

        ;; Create a command table
        (my-procs (make-hash-table 10))
        ;; Output port
        (page-out (open-output-file "page.out")))

       ;; Initialize command table
       (hash-set! my-procs 'comment
                  (lambda args ""))

       (hash-set! my-procs 'cool
                  (lambda (who)
                          (string-append who "is cool")))

       (hash-set! my-procs 'add +)

       ;; Parse page and write it to page.out
       (for-each (lambda (x) (display x page-out))
                 (template:parse my-procs my-file))

       (close-port page-out))

The page used by the script:

     [comment page.tmpl]
     Tra la la!
     [[This will be inside of square brackets]
     2 + 2 = [add 2 2]. I think that [cool Clinton]! He has a Camaro and
     wrote Guile-Web so he deserves mad props.

     Only he's not a hip-hop kid so he doesn't think that 2 + 2 = [add 2 3]
     or anything. Yeah. Also, this example really isn't that great.
     [comment Since comment is a multi-argument procedure, I can put
     whatever I want in here as long as it is a valid piece of Scheme data.]

GNU Free Documentation License
******************************

Version 1.2, November 2002

     Copyright © 2000,2001,2002 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA

     Everyone is permitted to copy and distribute verbatim copies
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     You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License.  Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License.  However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time.  Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.  See http://www.gnu.org/copyleft/.

     Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License ``or any later version'' applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation.  If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

ADDENDUM: How to use this License for your documents
----------------------------------------------------

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the ``with...Texts.'' line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.