Apache > HTTP Server > Documentation > Version 2.4 > Modules

Apache Module mod_so

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Description:Loading of executable code and modules into the server at start-up or restart time
Module Identifier:so_module
Source File:mod_so.c
Compatibility:This is a Base module (always included) on Windows


On selected operating systems this module can be used to load modules into Apache HTTP Server 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), on Windows this may either be the .so or .dll extension.


Modules built for one major version of the Apache HTTP Server will generally not work on another. (e.g. 1.3 vs. 2.0, or 2.0 vs. 2.2) There are usually API changes between one major version and another that require that modules be modified to work with the new version.

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Creating Loadable Modules for Windows


On Windows, where loadable files typically have a file extension of .dll, Apache httpd modules are called mod_whatever.so, just as they are on other platforms. However, you may encounter third-party modules, such as PHP for example, that continue to use the .dll convention.

While mod_so still loads modules with ApacheModuleFoo.dll names, the new naming convention is preferred; if you are converting your loadable module for 2.0, please fix the name to this 2.0 convention.

The Apache httpd 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 httpd for Windows does not have the Configure program of Apache httpd 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 httpd 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 AP_MODULE_DECLARE_DATA (defined in the Apache httpd header files) to your module's module record definition. For example, if your module has:

module foo_module;

Replace the above with:

module AP_MODULE_DECLARE_DATA 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 libhttpd.lib export library that is created when the libhttpd.dll shared library is compiled. You may also have to change the compiler settings to ensure that the Apache httpd header files are correctly located. You can find this library in your server root's modules directory. It is best to grab an existing module .dsp file from the tree to assure the build environment is configured correctly, or alternately compare the compiler and link options to your .dsp.

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

Description:Link in the named object file or library
Syntax:LoadFile filename [filename] ...
Context:server config, virtual host

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

Description:Links in the object file or library, and adds to the list of active modules
Syntax:LoadModule module filename
Context:server config, virtual host

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.

For example:

LoadModule status_module "modules/mod_status.so"

loads the named module from the modules subdirectory of the ServerRoot.

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