Editing Web server (section)

==== URL path translation to file system ====
Web server programs are able to translate an URL path (all or part of it), that refers to a physical file system path, to an [[Path (computing)|absolute path]] under the target website's root directory.<ref name="ws-static-rqs-root-dir" />

Website's root directory may be specified by a configuration file or by some internal rule of the web server by using the name of the website which is the [[URL#Syntax|host]] part of the URL found in HTTP client request.<ref name="ws-static-rqs-root-dir" />

Path translation to file system is done for the following types of web resources:
* a local, usually non-executable, file (static request for file content);
* a local directory (dynamic request: directory listing generated on the fly);
* a program name (dynamic requests that is executed using CGI or SCGI interface and whose output is read by web server and resent to client who made the HTTP request).

The web server appends the path found in requested URL (HTTP request message) and appends it to the path of the (Host) website root directory. On an [[Apache HTTP Server|Apache server]], this is commonly <code>/home/www/website</code> (on [[Unix]] machines, usually it is: <code>/var/www/website</code>). See the following examples of how it may result.

'''URL path translation for a static file request'''

Example of a ''static request'' of an existing file specified by the following URL:

 <nowiki>http://www.example.com/path/file.html</nowiki>

The client's [[user agent]] connects to <code><nowiki>www.example.com</nowiki></code> and then sends the following [[HTTP]]/1.1 request:
 GET <nowiki>/path/file.html</nowiki> HTTP/1.1
 <nowiki>Host: www.example.com</nowiki>
 Connection: keep-alive

The result is the local file system resource:

 <nowiki>/home/www/www.example.com/path/file.html</nowiki>

The web server then reads the [[Computer file|file]], if it exists, and sends a response to the client's web browser. The response will describe the content of the file and contain the file itself or an error message will return saying that the file does not exist or its access is forbidden.

'''URL path translation for a directory request (without a static index file)'''

Example of an implicit ''dynamic request'' of an existing directory specified by the following URL:

 <nowiki>http://www.example.com/directory1/directory2/</nowiki>

The client's [[user agent]] connects to <code><nowiki>www.example.com</nowiki></code> and then sends the following [[HTTP]]/1.1 request:
 GET <nowiki>/directory1/directory2</nowiki> HTTP/1.1
 <nowiki>Host: www.example.com</nowiki>
 Connection: keep-alive

The result is the local directory path:

 <nowiki>/home/www/www.example.com/directory1/directory2/</nowiki>

The web server then verifies the existence of the [[Directory (computing)|directory]] and if it exists and it can be accessed then tries to find out an index file (which in this case does not exist) and so it passes the request to an internal module or a program dedicated to directory listings and finally reads data output and sends a response to the client's web browser. The response will describe the content of the directory (list of contained subdirectories and files) or an error message will return saying that the directory does not exist or its access is forbidden.

'''URL path translation for a dynamic program request'''

For a ''dynamic request'' the URL path specified by the client should refer to an existing external program (usually an executable file with a CGI) used by the web server to generate dynamic content.<ref name="ws-dynamic-rqs-root-dir">{{Cite web|url=https://httpd.apache.org/docs/2.4/howto/cgi.html|title=Dynamic Content with CGI|publisher=Apache: HTTPd server project|year=2021|access-date=2021-10-19|language=en|archive-date=15 November 2021|archive-url=https://web.archive.org/web/20211115181448/https://httpd.apache.org/docs/2.4/howto/cgi.html|url-status=live}}</ref>

Example of a ''dynamic request'' using a program file to generate output:

 <nowiki>http://www.example.com/cgi-bin/forum.php?action=view&orderby=thread&date=2021-10-15</nowiki>

The client's [[user agent]] connects to <code><nowiki>www.example.com</nowiki></code> and then sends the following [[HTTP]]/1.1 request:
 GET <nowiki>/cgi-bin/forum.php?action=view&ordeby=thread&date=2021-10-15</nowiki> HTTP/1.1
 <nowiki>Host: www.example.com</nowiki>
 Connection: keep-alive

The result is the local file path of the program (in this example, a [[PHP]] program):

 <nowiki>/home/www/www.example.com/cgi-bin/forum.php</nowiki>

The web server executes that program, passing in the path-info and the [[query string]] <code>action=view&orderby=thread&date=2021-10-15</code> so that the program has the info it needs to run. (In this case, it will return an HTML document containing a view of forum entries ordered by thread from October 15, 2021). In addition to this, the web server reads data sent from the external program and resends that data to the client that made the request.