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HTTP Protocol

Early versions of the WWW developed a reputation as a versatile and convenient tool for accessing mission-critical data at the European Laboratory for Particle Physics (CERN).

Paradoxically the Web tools Tim Berners-Lee developed were the most successful and were widely regarded as the best way to access the CERN phone directory. Please note, that the first successful WWW application was not distribution of published papers it was a gateway to an existing and important application. Of course, the versatility of  WWW became clearer as the technology spread among high energy physics institutions and then to the outside world. But is it really an accident that the Web took off as a gateway to existing information system? I think this is not an accident and that's why WWW served as a launch pad for several scripting languages, including Perl, JavaScript, PHP and Python.

As Oleg Kiselyov noted in his Login - Speaking HTTP paper:

...HTTP is useful in its own right, for example, as a good file-distribution protocol with a number of important advantages over ftp. This article gives an example how to speak HTTP and get understood.

... By definition[1], HTTP is a request/response protocol that exchanges messages in a format similar to that used by Internet mail (MIME). An HTTP transaction is essentially a remote procedure call. It is usually a blocking call, although HTTP/1.1 provides for asynchronous and batch modes. HTTP allows intermediaries (caches, proxies) to cut into the response-reply chain.

An operation to execute remotely is expressed in HTTP as an application of a request method to a resource. Additional parameters, if needed, are communicated via request headers or a request body. The request body may be an arbitrary octet-stream. The HTTP/1.1 standard defines methods GET, HEAD, POST, PUT, DELETE, OPTIONS, TRACE, and CONNECT. A particular server may accept many others. This extensibility is a rather notable feature of HTTP. The parties can use not only custom methods but custom request and reply headers as well. In addition, a client and a server may exchange meta-information via "name=value" attribute pairs of the standard "Content-Type:" header.

Most of the HTTP transactions performed every day are done behind the scenes by browsers, proxies, robots, and servers. Yet the protocol is so simple that one can easily speak it oneself. The only requirement is a language or tool that is able to manipulate text strings and establish TCP connections. Even a simple telnet application may do in a pinch, which is often useful for debugging. Server-side programming is less demanding: a servlet or a scriptlet does not need to bother with the network connectivity, authentication, access restrictions, SSL, and other similar chores. Server modules or FastCGI give a server-side programmer even more tools: load-balancing, persistence, database connectivity, etc. This article demonstrates how to use Perl scripts to speak and respond HTTP directly.

News

• HTTP - Hypertext Transfer Protocol Overview

• UKOLN - WebWatch - HTTP-info
• HTTP Header Viewer
• Server-side programming tricks for client-side programmers
• Cache Now! details
• HTTP request mirror
• Accessible on the Web

Reference

• The World Wide Web Consortium has an excellent set of tools, doc format-to-html filters, editors, checkers, robots, administrative tools
• Web Developers Home Page.
• The Webmaster's Reference Library.
• The CGI Resource Index.
• Willcam's Comprehensive HTML Cross Reference
• Weblint, by Neil Bowers, syntax and minimal style checker for HTML. Also include pointers to HTML editors and link validation tools.