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Apache HTTP Server Version 1.3

Module mod_so

This module provides for loading of executable code and modules into the server at start-up or restart time.

Status: Base (Windows); Experimental (Unix)
Source File: mod_so.c
Module Identifier: so_module
Compatibility: Available in Apache 1.3 and later.


This is an experimental module. On selected operating systems it can be used to load modules into Apache at runtime via the Dynamic Shared Object (DSO) mechanism, rather than requiring a recompilation.

On Unix, the loaded code typically comes from shared object files (usually with .so extension), whilst on Windows this module loads DLL files. This module is only available in Apache 1.3 and up.

In previous releases, the functionality of this module was provided for Unix by mod_dld, and for Windows by mod_dll. On Windows, mod_dll was used in beta release 1.3b1 through 1.3b5. mod_so combines these two modules into a single module for all operating systems.


Creating DLL Modules for Windows

The Apache module API is unchanged between the Unix and Windows versions. Many modules will run on Windows with no or little change from Unix, although others rely on aspects of the Unix architecture which are not present in Windows, and will not work.

When a module does work, it can be added to the server in one of two ways. As with Unix, it can be compiled into the server. Because Apache for Windows does not have the Configure program of Apache for Unix, the module's source file must be added to the ApacheCore project file, and its symbols must be added to the os\win32\modules.c file.

The second way is to compile the module as a DLL, a shared library that can be loaded into the server at runtime, using the LoadModule directive. These module DLLs can be distributed and run on any Apache for Windows installation, without recompilation of the server.

To create a module DLL, a small change is necessary to the module's source file: The module record must be exported from the DLL (which will be created later; see below). To do this, add the MODULE_VAR_EXPORT (defined in the Apache header files) to your module's module record definition. For example, if your module has:

    module foo_module;

Replace the above with:

    module MODULE_VAR_EXPORT foo_module;

Note that this will only be activated on Windows, so the module can continue to be used, unchanged, with Unix if needed. Also, if you are familiar with .DEF files, you can export the module record with that method instead.

Now, create a DLL containing your module. You will need to link this against the ApacheCore.lib export library that is created when the ApacheCore.dll shared library is compiled. You may also have to change the compiler settings to ensure that the Apache header files are correctly located.

This should create a DLL version of your module. Now simply place it in the modules directory of your server root, and use the LoadModule directive to load it.

LoadFile directive

Syntax: LoadFile filename [filename] ...
Context: server config
Status: Base
Module: mod_so

The LoadFile directive links in the named object files or libraries when the server is started or restarted; this is used to load additional code which may be required for some module to work. Filename is either an absolute path or relative to ServerRoot.

For example:

LoadFile libexec/libxmlparse.so

LoadModule directive

Syntax: LoadModule module filename
Context: server config
Status: Base
Module: mod_so

The LoadModule directive links in the object file or library filename and adds the module structure named module to the list of active modules. Module is the name of the external variable of type module in the file, and is listed as the Module Identifier in the module documentation. Example (Unix, and for Windows as of Apache 1.3.15):

LoadModule status_module modules/mod_status.so

Example (Windows prior to Apache 1.3.15, and some 3rd party modules):

LoadModule foo_module modules/ApacheModuleFoo.dll

Note that all modules bundled with the Apache Win32 binary distribution were renamed as of Apache version 1.3.15.

Win32 Apache modules are often distributed with the old style names, or even a name such as libfoo.dll. Whatever the name of the module, the LoadModule directive requires the exact filename, no assumption is made about the filename extension.

See also: AddModule and ClearModuleList

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