IRCd Module Tree
This directory contains dynamically loadable functionality to libircd. Many of these modules provide essential application functionality, but are not always required to be directly linked and loaded into libircd proper. Most application- specific functionality (i.e "business logic") is contained in modules within this tree.
Layout
The modules/ directory tree is primarily shaped the same as the HTTP resource
tree in which most of its modules register themselves in.
Note that the installation layout is not the same as the development source
layout (i.e in git). Upon installation, the module tree is collapsed into a
single directory and installed into
$prefix/lib/modules/construct/$directory_$module.so; where directories are
replaced by underscores in the final SONAME. this may be subject to
improvement.
Approach
Unlike most of the module systems found in traditional free software projects, our approach is oriented around global symbol availability to the address space rather than explicit imports from self-contained modules. This direction is made viable by C++ and advances in the compiler and linker toolchains. The result is significantly simpler and more convenient for developers to work with.
-
Modules are loaded with
RTLD_GLOBALon both posix and windows platforms. Use of C++ namespaces, visibility attributes,STB_GNU_UNIQUE, etc are adequate to make this modernization. -
All project code is built to silently weaken undefined symbols. This means a complicated interface declared in a header, like a class interface with public and private and static members -- typical in C++ -- can be included by itself into any part of the project without knowing where the definitions of that interface are until they are first used at runtime. If said definitions are not available because they are in an unloaded module, a C++ exception is thrown directly from the callsite.
Getting started
The header mods/mapi.h is specific to modules and included for modules in
addition to the core ircd.h. Both of these are included automatically
via the compiler's command-line and the developer does not have to #include
either in the module.
Every loadable module requires a static ircd::mapi::header with the explicit
name of IRCD_MODULE. This is an object which will be sought by the module
loader in libircd. Nothing else is required.