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- add missing \label
- add errormessage generation to lonhelp.pm in case it does not find a label for
the reference
- This should fix #3016, and make it easier to find these errors in the fututre
1: \label{Guts_Apache}
2:
3: The standard mode in which the Apache web server is used is that a
4: URL corresponds to some static file on the file system, which then
5: more or less gets sent out as-is. Slight deviations from that simple
6: principle are however already the directory listing function, virtual
7: servers, and the cgi-bin directory. In the latter case, Apache executes
8: the file in a new process and provides both the input to the process
9: in the environment, and routes the output to the client. Other deviations
10: are the error messages.
11:
12: In a more general view, URLs to Apache are URIs (Uniform Resource
13: Identifiers), which may are may not correspond to a physical file,
14: which in turn may or may not be sent out as-is.
15:
16: As a request for a URI gets sent to the Apache server, it goes through
17: several phases. At each phase ({}``stage'') along the process, handler
18: modules can be defined to deal with the request. Details about these
19: phases are given in {}``Writing Apache Modules with Perl and C''
20: from O'Reilly (the {}``Eagle book'') in Chapter 3 (page 60).
21:
22: These handler modules are not like cgi-scripts executed in a separate
23: process, but are dynamically linked into the Apache child processes
24: themselves - they run inside of Apache. The mod\_perl mechanism in
25: addition links the Perl interpreter into the Apache child process.
26: Modules are pre-interpreted ({}``compiled'') by the Perl interpreter
27: when they are first loaded, and the pre-interpreted code stays permanently
28: in the memory allocated to that Apache child process. The result is
29: a significant speed-up, and through the flexible mechanism of module
30: registration and different stages of the process, a high degree of
31: customizability.
32:
33: LON-CAPA does \emph{not} use Apache::Registry, and so in addition
34: avoids the unnecessary overhead of emulating a cgi-environment within
35: the handlers. Instead, it makes direct use of the Apache Perl API
36: (Chapter 9, Eagle book).
37:
38: If you intend to add new capabilities to LON-CAPA that require new
39: handlers, as opposed to tweaking current ones, we recommend buying
40: a copy of {}``Writing Apache Modules with Perl and C''; it is not
41: strictly necessary but it is the clearest description of what is going
42: on in the Apache server, and without it you will be challenged to
43: understand everything that is occurring in the server.
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