Cytoplasm (libcytoplasm)

Cytoplasm is a general-purpose C library and runtime stub for creating high-level (particularly networked and multi-threaded) C applications. It allows applications to take advantage of the speed, flexibility, and simplicity of the C programming language, while providing helpful code to perform various complex tasks. Cytoplasm provides high-level data structures, a basic logging facility, an HTTP client and server, and more.

Cytoplasm aims not to only do one thing well, but to do many things good enough. The primary target of Cytoplasm is simple, yet higher level C applications that have to perform relatively complex tasks, but don't want to pull in a large number of dependencies.

Cytoplasm is extremely opinionated on the way programs using it are written. It strives to create a comprehensive and tightly-integrated programming environment, while also maintaining C programming correctness. It doesn't do any macro magic or make C look like anything other than C. It is written entirely in C89, and depends only on a POSIX environment. This differentiates it from other general-purpose libraries that often require modern compilers and non-standard language and environment features. Cytoplasm is intended to be extremely portable and simple, while still providing some of the functionality expected in higher-level programming languages in a platform-agnostic manner. In the case of TLS, Cytoplasm wraps low-level TLS libraries to offer a single, unified interface to TLS so that programs do not have to care about the underlying implementation.

Cytoplasm is probably not suitable for embedded programming. It makes liberal use of the heap, and while data structures are designed to conserve memory where possible and practical, minimal memory usage is not really a design goal for Cytoplasm, although Cytoplasm takes care not to use any more memory than it absolutely needs. Cytoplasm also wraps a few standard libraries with additional logic and checking. While this ensures better runtime safetly, this inevitably adds a little overhead.

Originally a part of Telodendria (https://telodendria.io), a Matrix homeserver written in C, Cytoplasm was split off into its own project due to the desire of some Telodendria developers to use Telodendria's code in other projects. Cytoplasm is still a Telodendria project, and is maintained along side of Telodendria itself, even living in the same CVS module, but it is designed specifically to be distributed and used totally independent of Telodendria.

The name "Cytoplasm" was chosen for a few reasons. It plays off the precedent set up by the Matrix organization in naming projects after the parts of a neuron. It also speaks to the function of Cytoplasm. The cytoplasm of a cell is the supporting material. It is what gives the cell its shape, and it facilitates the movement of materials to the other cell parts. Likewise, Cytoplasm aims to provide a support mechanism for C applications that have to perform complex tasks.

Cytoplasm also starts with a C, which I think is a nice touch for C libraries. It's also fun to say and unique enough that searching for "libcytoplasm" should bring you to this project and not some other one.

Building

If your operating system or software distribution provides a pre-built package of Cytoplasm, you should prefer to use that instead of building it from source.

Cytoplasm aims to have zero dependencies beyond what is mandated by POSIX. You only need the standard math and pthread libraries to build it. TLS support can optionally be enabled by setting the TLS_IMPL environment variable. The supported TLS implementations are as follows:

• OpenSSL
• LibreSSL

If TLS support is not enabled, all APIs that use it should fall back to non-TLS behavior in a sensible manner. For example, if TLS support is not enabled, then the HTTP client API will simply return an error if a TLS connection is requested. Cytoplasm uses a custom build script instead of Make, for the sake of portability. To build everything, just run the script:

$ sh make.sh

This will produce the following out/ directory:

    out/
        lib/
            libcytoplasm.so - The Cytoplasm shared library.
            libcytoplasm.a - The Cytoplasm static library.
            cytoplasm.o - The Cytoplasm runtime stub.
        bin/
            hdoc - The documentation generator tool.
        man/ - All Cytoplasm API documentation.

Usage

Cytoplasm provides the typical .so and .a files, which can be used to link programs with it in the usual way. However, Cytoplasm also provides a minimal runtime environment that is intended to be used with the library. As such, it also provides a runtime stub, which is intended to be linked in with programs using Cytoplasm. This stub is responsible for setting up and tearing down some Cytoplasm APIs. While it isn't required by any means, it makes Cytoplasm a lot easier to use for programmers by abstracting out all of the common logic that most programs will want to use.

Here is the canonical Hello World written with Cytoplasm:

    #include <Log.h>

    int Main(void)
    {
		Log(LOG_INFO, "Hello World!");
		return 0;
	}

If this file is Hello.c, then you can compile it by doing something like this:

$ cc -o hello Hello.c cytoplasm.o -lcytoplasm

This command assumes that the runtime stub resides in the current working directory, and that libcytoplasm.so is in your library path. If you're using the version of Cytoplasm installed by your operating system or software distribution, consult the documentation for the location of the runtime stub. It may be located in /usr/local/libexec or some other similar location. If you've built Cytoplasm from source and wish to link to it from there, you may wish to do something like this:

$ export CYTOPLASM=/path/to/Cytoplasm/out/lib
$ cc -o hello Hello.c "${CYTOPLASM}/cytoplasm.o" \
    "-L${CYTOPLASM}" -lcytoplasm

As you may have noticed, C programs using Cytoplasm's runtime stub don't write the main() function. Instead, they use Main(). The main() function is provided by the runtime stub. The full form of Main() expected by the stub is as follows:

	int Main(Array *args, HashMap *env);

The first argument is a Cytoplasm array of the command line arguments, and the second is a Cytoplasm hash map of environment variables. Most linkers will let programs omit the env argument, or both arguments if you don't need either. The return value of Main() is returned to the operating system.

Note that both arguments to Main may be treated like any other array or hash map. However, do not invoke ArrayFree() or HashMapFree() on the passed pointers, because memory is cleaned up after Main() returns.