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RPC over RabbitMQ/AMQP

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amqprpc.js
JavaScript
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var amqp = require('amqp')
, crypto = require('crypto')
 
var TIMEOUT=2000; //time to wait for response in ms
var CONTENT_TYPE='application/json';
var CONTENT_ENCODING='utf-8';
 
exports = module.exports = AmqpRpc;
 
function AmqpRpc(connection){
var self = this;
this.connection = connection;
this.requests = {}; //hash to store request in wait for response
this.response_queue = false; //plaseholder for the future queue
}
 
AmqpRpc.prototype.makeRequest = function(queue_name, content, callback){
var self = this;
//generate a unique correlation id for this call
var correlationId = crypto.randomBytes(16).toString('hex');
//create a timeout for what should happen if we don't get a response
var tId = setTimeout(function(corr_id){
//if this ever gets called we didn't get a response in a
//timely fashion
callback(new Error("timeout " + corr_id));
//delete the entry from hash
delete self.requests[corr_id];
}, TIMEOUT, correlationId);
 
//create a request entry to store in a hash
var entry = {
callback:callback,
timeout: tId //the id for the timeout so we can clear it
};
//put the entry in the hash so we can match the response later
self.requests[correlationId]=entry;
 
//make sure we have a response queue
self.setupResponseQueue(function(){
//put the request on a queue
self.connection.publish(queue_name, content, {
correlationId:correlationId,
contentType:CONTENT_TYPE,
contentEncoding:CONTENT_ENCODING,
replyTo:self.response_queue});
});
}
 
 
AmqpRpc.prototype.setupResponseQueue = function(next){
//don't mess around if we have a queue
if(this.response_queue) return next();
 
var self = this;
//create the queue
self.connection.queue('', {exclusive:true}, function(q){
//store the name
self.response_queue = q.name;
//subscribe to messages
q.subscribe(function(message, headers, deliveryInfo, m){
//get the correlationId
var correlationId = m.correlationId;
//is it a response to a pending request
if(correlationId in self.requests){
//retreive the request entry
var entry = self.requests[correlationId];
//make sure we don't timeout by clearing it
clearTimeout(entry.timeout);
//delete the entry from hash
delete self.requests[correlationId];
//callback, no err
entry.callback(null, message);
}
});
return next();
});
}
client.js
JavaScript
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//exmaple on how to use amqprpc
var amqp = require('amqp');
var connection = amqp.createConnection({host:'127.0.0.1'});
 
var rpc = new (require('./amqprpc'))(connection);
 
connection.on("ready", function(){
console.log("ready");
var outstanding=0; //counter of outstanding requests
 
//do a number of requests
for(var i=1; i<=10 ;i+=1){
//we are about to make a request, increase counter
outstanding += 1;
rpc.makeRequest('msg_queue', {foo:'bar', index:outstanding}, function response(err, response){
if(err)
console.error(err);
else
console.log("response", response);
//reduce for each timeout or response
outstanding-=1;
isAllDone();
});
}
 
function isAllDone() {
//if no more outstanding then close connection
if(outstanding === 0){
connection.end();
}
}
 
});
server.js
JavaScript
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//super simple rpc server example
var amqp = require('amqp')
, util = require('util');
 
var cnn = amqp.createConnection({host:'127.0.0.1'});
 
cnn.on('ready', function(){
console.log("listening on msg_queue");
cnn.queue('msg_queue', function(q){
q.subscribe(function(message, headers, deliveryInfo, m){
util.log(util.format( deliveryInfo.routingKey, message));
//return index sent
cnn.publish(m.replyTo, {response:"OK", index:message.index}, {
contentType:'application/json',
contentEncoding:'utf-8',
correlationId:m.correlationId
});
});
});
});

I originally made this code as an answer to a question on stackoverflow.

http://stackoverflow.com/questions/10524613/how-to-create-rep-req-on-rabbit-js/

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