3 KiB
IRCd Library
This library can be embedded by developers creating their own server or those
who simply want to use the library of routines it provides. See the section for
Using libircd.
The purpose of libircd is to facilitate the execution of a server which
handles requests from end-users. The library hosts a set of pluggable modules
which may introduce the actual application features (or the "business logic")
of the server. These additional modules are found in the modules/ directory;
Using libircd
libircd can be embedded in your application with very minimal overhead.
This allows you to customize and extend the functionality of the server and have
control over its execution, or, simply use library routines provided by the library
without any daemonization. Including libircd headers will not include any other
headers beyond those in the standard library, with minimal impact on your project's
compile complexity. The prototypical embedding of libircd is charybdis found in
the charybdis/ directory.
libircd runs only one server at a time.
Keeping with the spirit of simplicity of the original architecture, libircd
continues to be a "singleton" object which uses globals and keeps actual server
state in the library itself. In other words, only one IRC daemon can exist
within a process's address space at a time. This is actually a profitable
design decision for making IRCd easier to understand for contributors.
libircd is single-threaded✝
The library is based around the boost::asio::io_service event loop. It is still
an asynchronous event-based system. We process one event at a time; developers must
not block execution. Events are never processed concurrently on different threads✝.
However, there are some ✝'s here which must be addressed. We have introduced additional standard threads to libircd with the purpose of "offloading" operations from some library dependencies that don't cooperate asynchronously. This ensures the "main thread" running the actual event loop is never blocked in any case. Furthermore, some 3rd party dependencies like RocksDB (and boost::asio's DNS resolver) may introduce threads into the address space which they handle privately.
libircd introduces userspace threading
IRCd presents an interface introducing stackful coroutines, a.k.a. userspace context switching, or green threads. The library does not use callbacks as the way to break up execution when waiting for events. Instead, we harken back to the simple old ways of synchronous programming, where control flow and data are easy to follow.
libircd innovates with formal grammars
We leverage the boost::spirit system of parsing and printing through formal grammars, rather than writing our own parsers manually. In addition, we build several tools on top of such formal devices like a type-safe format string library acting as a drop-in for ::sprintf(), but accepting objects like std::string without .c_str() and prevention of outputting unprintable/unwanted characters that may have been injected into the system somewhere prior.