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1.1     ! bowersj2    1: The standard mode in which the Apache web server is used is that a
        !             2: URL corresponds to some static file on the file system, which then
        !             3: more or less gets sent out as-is. Slight deviations from that simple
        !             4: principle are however already the directory listing function, virtual
        !             5: servers, and the cgi-bin directory. In the latter case, Apache executes
        !             6: the file in a new process and provides both the input to the process
        !             7: in the environment, and routes the output to the client. Other deviations
        !             8: are the error messages.
        !             9: 
        !            10: In a more general view, URLs to Apache are URIs (Uniform Resource
        !            11: Identifiers), which may are may not correspond to a physical file,
        !            12: which in turn may or may not be sent out as-is.
        !            13: 
        !            14: As a request for a URI gets sent to the Apache server, it goes through
        !            15: several phases. At each phase ({}``stage'') along the process, handler
        !            16: modules can be defined to deal with the request. Details about these
        !            17: phases are given in {}``Writing Apache Modules with Perl and C''
        !            18: from O'Reilly (the {}``Eagle book'') in Chapter 3 (page 60).
        !            19: 
        !            20: These handler modules are not like cgi-scripts executed in a separate
        !            21: process, but are dynamically linked into the Apache child processes
        !            22: themselves - they run inside of Apache. The mod\_perl mechanism in
        !            23: addition links the Perl interpreter into the Apache child process.
        !            24: Modules are pre-interpreted ({}``compiled'') by the Perl interpreter
        !            25: when they are first loaded, and the pre-interpreted code stays permanently
        !            26: in the memory allocated to that Apache child process. The result is
        !            27: a significant speed-up, and through the flexible mechanism of module
        !            28: registration and different stages of the process, a high degree of
        !            29: customizability.
        !            30: 
        !            31: LON-CAPA does \emph{not} use Apache::Registry, and so in addition
        !            32: avoids the unnecessary overhead of emulating a cgi-environment within
        !            33: the handlers. Instead, it makes direct use of the Apache Perl API
        !            34: (Chapter 9, Eagle book).
        !            35: 
        !            36: If you intend to add new capabilities to LON-CAPA that require new
        !            37: handlers, as opposed to tweaking current ones, we recommend buying
        !            38: a copy of {}``Writing Apache Modules with Perl and C''; it is not
        !            39: strictly necessary but it is the clearest description of what is going
        !            40: on in the Apache server, and without it you will be challenged to
        !            41: understand everything that is occurring in the server.