Wapp

Wapp - A Web-Application Framework for TCL
==========================================

1.0 Introduction
----------------

Wapp is a lightweight framework that strives to simplify the
construction of web application written in TCL. The same Wapp-based
application can be launched in multiple ways:

  1.  From the command-line (ex: "<tt>tclsh app.tcl</tt>").  In this mode,
      The wapp finds an available TCL port on localhost, starts an
      in-process web server listening on that port, and then launches the 
      users default web browser directed at localhost:$port

  2.  As a stand-alone web server

  3.  As a CGI script

  4.  As an SCGI program

All four methods use the same application code and present the same
interface to the application user.  An application can be developed on
the desktop using stand-alone mode (1), then deployed as a stand-alone
server (2), or a CGI script (3), or as an SCGI program (4).

2.0 Hello World!
----------------

Wapp is designed to be easy to use.  A hello-world program is as follows:

>
    package require wapp
    proc wapp-default {req} {
       wapp "<h1>Hello, World!</h1>\n"
    }
    wapp-start $::argv

The application defines one or more procedures that accept HTTP requests
and generate appropriate replies.
For an HTTP request where the initial portion of the URI is "abcde", the
procedure named "wapp-page-abcde" will be invoked to construct the reply.
If no such procedure exists, "wapp-default" is invoked instead.  The latter
technique is used for the hello-world example above.

The procedure generates a reply using one or more calls to the "wapp"
command.  Each "wapp" command appends new text to the reply.

The "wapp-start" command starts up the application.

To run this application, copy the code above into a file named "main.tcl"
and then enter the following command:

>
    tclsh main.tcl

That command will start up a web-server bound to the loopback
IP address, then launch a web-browser pointing at that web-server.
The result is that the "Hello, World!" page will automatically
appear in your web browser.

To run this same program as a traditional web-server on TCP port 8080, enter:

>
    tclsh main.tcl --server 8080

Here the built-in web-server listens on all IP addresses and so the
web page is available on other machines.  But the web-broswer is not
automatically started in this case, so you will have to manually enter
"http://localhost:8080/" into your web-browser in order to see the page.

To run this program as CGI, put the main.tcl script in your web-servers
file hierarchy, in the appropriate place for CGI scripts, and make any
other web-server specific configuration changes so that the web-server
understands that the main.tcl file is a CGI script.  Then point your
web-browser at that script.

Run the hello-world program as SCGI like this:

>
    tclsh main.tcl --scgi 9000

Then configure your web-server to send SCGI requests to TCL port 9000
for some specific URI, and point your web-browser at that URI.

3.0 A Slightly Longer Example
-----------------------------

Information about each HTTP request is encoded in the global ::wapp
dict variable.  The following sample program shows the information
available in ::wapp.

>
    package require wapp

The /env page is implemented by the "wapp-page-env" proc.  This proc
generates an HTML that describes the content of the ::wapp dict.
Keys that begin with "." are for internal use by Wapp and are skipped
for this display. The "wapp-escape-html"
command is like "wapp" and "wapp-unsafe" except that "wapp-escape-html"
escapes HTML markup so that it displays correctly in the output.

4.0 The ::wapp Global Dict
--------------------------

To better understand how the ::wapp dict works, try running the previous
sample program, but extend the /env URL with extra path elements and query
parameters.  For example:
<http://localhost:8080/env/longer/path?q1=5&title=hello+world%21>

Notice how the query parameters in the input URL are decoded and become
elements of the ::wapp dict.  The same thing occurs with POST parameters
and cookies - they are all converted into entries in the ::wapp dict
variable so that the parameters are easily accessible to page generation
procedures.

The ::wapp dict contains additional information about the request,
roughly corresponding to CGI environment variables.  To prevent environment
information from overlapping and overwriting query parameters, all the
environment information uses upper-case names and all query parameters
are required to be lower case.  If an input URL contains an upper-case
query parameter (or POST parameter or cookie), that parameter is silently
omitted from the ::wapp dict.

The ::wapp dict contains the following environment values:

  +  **HTTP\_HOST**  
     The hostname (or IP address) and port that the client used to create
     the current HTTP request.  This is the first part of the request URL,
     right after the "http://" or "https://".  The format for this value

     All of PATH\_INFO that follows PATH\_HEAD.

  +  **SELF\_URL**  
     The URL for the current page, stripped of query parameter. This is
     useful for filling in the action= attribute of forms.


### 4.1 URL Parsing Example

For the input URL "http://example.com/cgi-bin/script/method/extra/path?q1=5"
and for a CGI script named "script" in the /cgi-bin/ directory, 
the following CGI environment values are generated:

  +  **HTTP\_HOST** → "example.com:80"
  +  **SCRIPT\_NAME** → "/cgi-bin/script"
  +  **PATH\_INFO** → "/method/extra/path"
  +  **REQUEST\_URI** → "/cgi-bin/script/method/extra/path"
  +  **QUERY\_STRING** → "q1=5"
  +  **BASE\_URL** → "http://example.com/cgi-bin/script"
  +  **SELF\_URL** → "http://example.com/cgi-bin/script/method"
  +  **PATH\_HEAD** → "method"
  +  **PATH\_TAIL** → "extra/path"

The first five elements of the example above, HTTP\_HOST through
QUERY\_STRING, are standard CGI.  The final four elements are Wapp
extensions.

5.0 Wapp Commands
-----------------

The following utility commands are available for use by applications built
on Wapp:

  +  **wapp-start** _ARGLIST_  
     Start up the application.  _ARGLIST_ is typically the value of $::argv,
     though it might be some subset of $::argv if the containing application

     command should only be used during debugging, as otherwise it introduces
     a severe security vulnerability into the application.

  *  **wapp-safety-check**  
     Examine all TCL procedures in the application and report errors about
     unsafe usage of "wapp".

6.0 Design Rules
----------------

All global procs and variables used by Wapp begin with the four character
prefix "wapp".  Procs and variable intended for internal use begin with
the seven character prefix "wappInt".

  }
  return $res
}

# Start up the wapp framework.  Parameters are a list passed as the
# single argument.
#
#    -server $PORT         Listen for HTTP requests on this TCP port $PORT
#
#    -scgi $PORT           Listen for SCGI requests on TCP port $PORT
#

#    -cgi                  Perform a single CGI request
#
# With no arguments, the behavior is called "auto".  In "auto" mode,
# if the GATEWAY_INTERFACE environment variable indicates CGI, then run
# as CGI.  Otherwise, start an HTTP server bound to the loopback address
# only, on an arbitrary TCP port, and automatically launch a web browser
# on that TCP port.
#
proc wapp-start {arglist} {
  global env
  set mode auto
  set port 0
  set n [llength $arglist]
  for {set i 0} {$i<$n} {incr i} {
    set term [lindex $arglist $i]
    if {[string match --* $term]} {set term [string range $term 1 end]}
    switch -- $term {
      -server {
        incr i;
        set mode "server"
        set port [lindex $arglist $i]
      }
      -scgi {
        incr i;
        set mode "scgi"
        set port [lindex $arglist $i]


      }
      -cgi {
        set mode "cgi"
      }
      default {
        error "unknown option: $term"
      }
    }
  }
  if {($mode=="auto"
       && [info exists env(GATEWAY_INTERFACE)]
       && $env(GATEWAY_INTERFACE)=="CGI/1.0")
    || $mode=="cgi"
  } {