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

Summary

On selected operating systems this module 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), on Windows this may either the .so or .dll extension. 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.

Warning: Apache 1.3 modules cannot be directly used with Apache 2.0 - the module must be modified to dynamically load or compile into Apache 2.0.

Directives

• LoadFile
• LoadModule

Creating Loadable Modules for Windows

Note: the module name format changed for Windows with Apache 1.3.15 and 2.0 - the modules are now named as mod_foo.so. 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 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 AP_MODULE_DECLARE_DATA (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 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 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

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 and absolute path or relative to ServerRoot.

LoadModule directive

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:

LoadModule status_module modules/mod_status.so

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