zdiscgo - Go plugin support for service discovery for CZMQ

Problem

I want to use various service discovery mechanisms with CZMQ, such as consul and mesos-dns. These APIs do not have good straight C client libraries but do have excellent Go libraries

Solution

zdiscgo - a CZMQ actor service that runs as a thread in a C application, and proxies service discovery lookup calls to dynamically loaded and bound Go libraries.

Why Did You Do This What Is Wrong With You

As Larry Wall said, the first great virtue of a programmer is laziness. If C can talk to Go and Go libraries exist for what I want to do, why not use them.

You might feel compelled to point out this all looks like more trouble than just writing some C client libraries, and that in fact I was not being lazy at all. In retort, I would note that Larry Wall also said the third great virtue of a programmer is hubris, of which this project contains plenty.

Status

Draft. API will change.

Building on Ubuntu

Installing prerequisites:

    sudo apt-get update
    sudo apt-get install -y \
    git-all build-essential libtool \
    pkg-config autotools-dev autoconf automake cmake \
    uuid-dev

    # only execute this next line if interested in updating the man pages as
    # well (adds to build time):
    sudo apt-get install -y asciidoc

libsodium

    git clone --depth 1 -b stable https://github.com/jedisct1/libsodium.git
    cd libsodium
    ./autogen.sh && ./configure && make check
    sudo make install
    cd ..

libzmq

    git clone git://github.com/zeromq/libzmq.git
    cd libzmq
    ./autogen.sh
    # do not specify "--with-libsodium" if you prefer to use internal tweetnacl
    # security implementation (recommended for development)
    ./configure --with-libsodium
    make check
    sudo make install
    sudo ldconfig
    cd ..

czmq

    git clone git://github.com/zeromq/czmq.git
    cd czmq
    ./autogen.sh && ./configure && make check
    sudo make install
    sudo ldconfig
    cd ..

zdiscgo

    git clone git://github.com/zeromq/czmq.git
    cd czmq
    ./autogen.sh && ./configure && make check
    sudo make install
    sudo ldconfig
    cd ..

Writing a Go Plugin

Go plugins should export a DiscoverEndpoints function:

package main

import "C"
import "fmt"

//export ZDiscgoDiscoverEndpoints
func ZDiscgoDiscoverEndpoints(url, key string) *C.char {
	return C.CString(fmt.Sprintf("inproc://%s-%s", url, key))
}

func main() {}

Using zdiscgo

#include <zdiscgo.h>

int main (int argc, char *argv [])
{
    //  Create a zdiscgo instance. This will spin up a new OS level
    //  thread that will handle service discovery requests.

    zactor_t *zdiscgo = zactor_new (zdiscgo_actor, NULL);

    // Set the actor to  verbose mode

    zdiscgo_verbose (zdiscgo);

    // Load a go library
    
    int rc = zdiscgo_load_plugin (zdiscgo, "./go/libmockdiscgo.so");
    assert (rc == 0);

    // Ask for a list of zeromq endpoints

    char *endpoints = zdiscgo_discover (zdiscgo, "url", "key");

    //  Check that we have the correct response

    assert (streq (endpoints, "inproc://url-key"));

    //  Shut down the zdisgco instance and clean up memory.

    zactor_destroy (&zdiscgo);
}

License

MPLv2

zeromq/zdiscgo