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Adding some .tex files in. (LPML addition later; still some to go.)

    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.