zmqd – a ZeroMQ wrapper for the D programming language

zmqd is a D library that wraps the low-level C API of the ZeroMQ messaging framework. It is a rather thin wrapper that maps closely to the C API, while making it safer, easier and more pleasant to use. Here's how:

• Errors are signalled by means of exceptions rather than return codes.
• Functions are appropriately marked with @safe, pure and nothrow, thus facilitating their use in high-level D code.
• Memory and resources (i.e. contexts, sockets and messages) are automatically managed, thus preventing leaks.
• Context, socket and message options are implemented as properties.

The names of functions and types in zmqd are very similar to those in ZeroMQ, but they follow the D naming conventions. Thus, the library should feel both familiar to ZeroMQ users and natural to D users.

Documentation

The API documentation may be browsed online at https://kyllingstad.github.io/zmqd/.

To build the documentation from source using Dub and DDOX, run the following command:

dub build --build=ddox

See the changelog for a list of the features that have been added or changed, and the bugs that have been fixed, in each release.

Terms of use

zmqd is free and open-source software, released under the terms of the Mozilla Public License v. 2.0. This allows you to mix it with other files under a different, even proprietary licence. However, the source code files of zmqd itself, and any modifications you make to them, must remain under the MPL and freely available in source form. For more information, see Mozilla's MPL FAQ.

Support and contributions

If you have questions, enhancement requests or bug reports, please submit them as issues on GitHub. Bug fixes in the form of pull requests are very welcome.

Requirements

What you need is:

• A somewhat up-to-date D compiler
• The ZeroMQ libraries
• The ZeroMQ C library bindings from Deimos

Tell the compiler where to find the libraries and the import files, and you're good to go.

It is of course also possible to use Dub to install the zmqd package and its dependencies, or to use it to build zmqd from source.

A word of caution about the C library bindings

As mentioned, you need the ZeroMQ C bindings to be able to build and use zmqd. If you use Dub, a compatible version of the C library bindings will automatically be fetched. However, this is not not necessarily compatible with the ZeroMQ library version you have installed. There are known ABI incompatibilities between different versions of ZeroMQ (different minor versions, even) so it is a good idea to make sure these match. With Dub, the appropriate version of the ZeroMQ bindings can be selected by modifying the file dub.selections.json (package zeromq). If you build manually, make sure to check out the correct version from the repository (it has version number tags).

To help detect incompatibilities, the zmqd unittests include a simple compatibility check which warns about possible problems. The simplest way to run the tests is to use Dub, as follows:

dub test zmqd

Note that some of the unittests will fail if your ZeroMQ library was not built with Curve support. (This is typically only an issue with ZeroMQ v4.0.x.) To disable these tests, use the debug specifier ZMQD_DisableCurveTests, e.g. like this:

dub test --debug=ZMQD_DisableCurveTests zmqd

Example: Hello World server

The C implementation of the "Hello World server" from the ZeroMQ Guide looks like this:

// Hello World server

#include <zmq.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <assert.h>

int main (void)
{
    // Socket to talk to clients
    void *context = zmq_ctx_new ();
    void *responder = zmq_socket (context, ZMQ_REP);
    int rc = zmq_bind (responder, "tcp://*:5555");
    assert (rc == 0);

    while (1) {
        char buffer [10];
        zmq_recv (responder, buffer, 10, 0);
        printf ("Received Hello\n");
        sleep (1); // Do some 'work'
        zmq_send (responder, "World", 5, 0);
    }
    return 0;
}

The equivalent zmqd program looks like this:

import core.thread, core.time;
import std.stdio;
import zmqd;

void main()
{
    // Socket to talk to clients
    auto responder = Socket(SocketType.rep);
    responder.bind("tcp://*:5555");

    while (true) {
        ubyte[10] buffer;
        responder.receive(buffer);
        writeln("Received Hello");
        Thread.sleep(1.seconds);
        responder.send("World");
    }
}

Note how Socket does not need a context, because the library creates a global "default context", since this is what the majority of programs will do anyway. Of course, if we wanted to, we could replace the first line of main() with the following:

auto context = Context();
auto responder = Socket(context, SocketType.rep);

More examples may be found in the examples subdirectory.