zdiscgo

CZMQ service discovery zactor with support for Go plugins.

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.

Writing a Go Plugin

Go plugins should export a DiscoverEndpoints function:

package main

import "C"
import "fmt"

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

func main() {}

Using zdiscgo

//  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);

//  We communicate with the service discovery thread over
//  a ZMQ_PAIR socket. You can pass the zdisgco instance
//  to any CZMQ methods that accept zsock_t *. 
//  Let's set the service to verbose mode.

zdiscgo_verbose (zdiscgo);

//  Next, let's configure the service by telling it to load 
//  our go shared library. The zstr_sendx command will send
//  multiple string frames. A NULL terminates the message.
    
zdiscgo_load_plugin (zdiscgo, "./go/libmockdiscgo.so");
assert (rc == 0);

//  Now let's get some endpoints! We send a DISCOVER command
//  that consists of the url of a service discovery service,
//  and the identifer the service should use to find the 
//  endpoints we want.

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