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CERN server directives

The CERN server uses a set of rules for mapping from a URL in an HTTP request to a physical file. The rules are applied in the order they appear in the configuration file until a request has been explicitly accepted or rejected, or there are no more rules to apply.

The URL in the HTTP request forms the initial request string. The rules specify pattern templates, against which the request string is matched. The Map, Pass, Exec and Redirect rules also specify a replacement template, which may be substituted for all or part of the original string (the replacement template is optional for the Pass directive). Asterisks are used as wildcards in the pattern templates, to match substrings in the request string. If matches are found the request string is replaced with the contents of the replacement template. Where the replacement template contains asterisks, the corresponding substrings of the original request string are retained. The following set of mapping rules illustrates some of the possibilities:

  Map      /misc/* /disk2/misc/*                           # 1
  Fail     /disk2/misc/new/*                               # 2
  Pass     /disk2/misc/part1/* /disk2/part1/*              # 3
  Redirect /disk2/misc/part2/* http://othersite.org/temp/* # 4
  Pass     /disk2/misc/part3/*                             # 5

In the example above:

• A request with a URL of /misc/new/doc.html, by virtue of rule 1, will be mapped to /disk2/misc/new/doc.html and then rejected by rule 2.

• A request with a URL of /misc/part1/doc.html will be mapped to /disk2/misc/part1/doc.html by rule 1 and then accepted by rule 3 and simultaneously mapped to /disk2/part1/doc.html.

• A request with a URL of /misc/part2/doc.html will be mapped to /disk2/misc/part2/doc.html by rule 1 and then redirected to the server othersite.org by rule 4.

• A request with a URL of /misc/part3/doc.html will be mapped to /disk2/misc/part3/doc.html by rule 1 and then accepted without further remapping by rule 5.

• A request with a URL of /misc/part4/doc.html will be mapped to /disk2/misc/part4/doc.html by rule 1 and then, as it matches no further rules, accepted if that file exists.

Map pattern replacement

Maps request strings that match the pattern template according to the replacement template.

    Map /misc/* /disk2/misc/*

There is no equivalent NCSA directive.

Pass pattern [replacement]

If the current request string matches the specified pattern, it is accepted and further mapping rules are ignored. If a replacement is specified, the part of the request string matching the pattern is replaced with the replacement:

    Pass /depts/sales/*

    Pass /depts/sales/* /usr/depts/sales/*

Analogous to the NCSA Alias directive.

Fail pattern

If the current request string matches the specified pattern, it is rejected. All further mapping rules are ignored.

    Fail /depts/sales/confidential/*

There is no equivalent NCSA directive.

Redirect pattern replacement

If the current request string matches the specified pattern, the request is redirected to another server.

    Redirect /sales/* http://othersite.org/usr/depts/sales/*

Equivalent to the NCSA Redirect directives.

Spinning the Web by Andrew Ford
© 1995 International Thomson Publishing
© 2002 Andrew Ford and Ford & Mason Ltd
Note: this HTML document was generated in December 1994 directly from the LaTeX source files using LaTeX2HTML. It was formatted into our standard page layout using the Template Toolkit. The document is mainly of historical interest as obviously many of the sites mentioned have long since disappeared.