The HTTP 1.0 Protocol

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The HTTP 1.0 Protocol

HTTP defines communication by a client and a WWW server. All HTTP 1.0 transactions follow a similar general format:

There is a first request line (from the client) or response line (from the server)
Then there are a few header lines (e.g. to give information about the client or server, to indicate following contents). The header always ends with a blank line.
Finally there can be a ``body'' section containing contents (user data from the client or response from the server).

The client contacts the server at a designated port number (by default this port number is 80, at TECFAMOO it is 7778 (for E_Web) or 7777 (for WOO). Next it sends a document request with a method indicating which document (or program) to fetch and with which protocol. HTTP 1.0 defines three main methods:

GET is a request for information located at a specific place (i.e. a Universal Ressource Identifier, URI). URIs are basically URLs.
The POST method allows client request data to be sent to the server. Note that a client can also send data to the server by appending it to the URL of a GET request (you will see that later).
The HEAD method works like GET but is only used to retrieve document or ressource header information (e.g. contents inside the <HEAD>....</HEAD> of a HTML document.

Here is a typical example of a GET file request to a standard www server

   GET /tecfamoo/welcome.html HTTP/1.0

and here the same to our E_Web interface:

   GET /4848 HTTP/1.0

Next, the client will send optional header information to tell the server more about its configuration, the server's internet machine host name or number, the document formats it will accept, etc. Here is a typical request from a client with the ``GET method'':

GET /4848 HTTP/1.0
Connection: Keep-Alive
User-Agent: Mozilla/3.01 (X11; I; SunOS 5.4 sun4m)
Pragma: no-cache
Host: tecfa.unige.ch:7778
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*

A typical request from a client with the ``POST method'':

POST /cgi/4848 HTTP/1.0
Referer: http://tecfa.unige.ch:7778/4848
Connection: Keep-Alive
User-Agent: Mozilla/3.01 (X11; I; SunOS 5.4 sun4m)
Host: tecfa.unige.ch:7778
Accept: image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, */*
Content-type: application/x-www-form-urlencoded
Content-length: 42

name=Daniel&age=old&string=Hello+there+%21

In section 8.7.2 you will see how user data is encoded with CGI.

Server response:

The server also replies by first sending a status line , header information about itself and the contents, follwed by a blank line and the contents.

The status line contains three fields: HTTP version, status code, and a more human readable description. Status code is a 3 digit number and there exist a lot of them. Here are a few examples:

200 OK The client's request was successful

and server's response contains the requested data

302 Moved Temporarily The requested URI must be taken as indicated in the ``Location'' header,

but the URL is fine for reuse

404 Not Found The requested document was not found

500 Internal Server Error You wrote some bad CGI that breaks:)

Table 8.1: Some HTTP status codes

**Table 8.1:** Some HTTP status codes
200 OK	The client's request was successful
and server's response contains the requested data
302 Moved Temporarily	The requested URI must be taken as indicated in the ``Location'' header,
but the URL is fine for reuse
404 Not Found	The requested document was not found
500 Internal Server Error	You wrote some bad CGI that breaks:)

Here is a typical reply from the E_Web interface:

HTTP/1.0 200 ok
Date: Wed, 16 Apr 97 22:54:42 GMT
Server: E_WEB (E_MOO-Web-Server/1.2d - Not WOO) (LambdaMOO 1.8.0p5)
Content-type: text/html

<title>Query results</title>
<h1>Query results</h1>
 ......

Here is another one from E_Web that shows a 500 status internal error. It also shows that debugging CGI code is quite easy with E_Web.

HTTP/1.0 500 internal error
Server: E_WEB (E_MOO-Web-Server/1.2d - Not WOO) (LambdaMOO 1.8.0p5)
Date: Thu, 17 Apr 97 11:06:09 GMT
MIME-version: 1.0
Content-type: text/html

<title>Error #500 internal error
 (http://tecfamoo.unige.ch:7778/cgi/4848)</title>
<h1>Error #500 internal error</h1>"
...........

The formated content as seen by the user will be like the following (references to moo verbs are links!)

Error #500 internal error

URL requested: http://tecfamoo.unige.ch:7778/cgi/4848 
Reference code: #-6034:861271377 

If you feel that you shouldn't have gotten this error, please report it to WebMaster.

POST attempt tracebacked with:
4848:cgi_query, line 9: Variable not found (E_VARNF)
... called from 4361:html_cgi, line 23
... called from 4361:http_request, line 6
... called from $ehttpd:POST, line 19
... called from $ehttpd:handle_request, line 22
(End of traceback for task 1285009894)

After completing the request, the server will close the connection.

Now in order to write dynamic responses to user requests you need to learn how to write CGI programs.

Next: Introduction to CGI Up: 8.7 A crash course Previous: 8.7 A crash course

Daniel K. Schneider
Thu Apr 17 12:43:52 MET DST 1997

The HTTP 1.0 Protocol

Client requests:

Server response: