CODEWITHSUNDEEP
node.js
Phani Kumar
Phani Kumar

Reputation: 450

Handle new TCP connections synchronously

I know nodejs is asynchronous by nature and it is preferable to use that way, but I have a use case where we need to handle incoming TCP connections in synchronous way. Once a new connections received we need to connect to some other TCP server and perform some book keeping stuff etc and then handle some other connection. Since number of connections are limited, it is fine to handle this in synchronous way.

Looking for an elegant way to handle this scenario.

net.createServer(function(sock) {
    console.log('Received a connection - ');
    var sock = null;
    var testvar = null;        

    sock = new net.Socket();        
    sock.connect(PORT, HOST, function() {
        console.log('Connected to server - ');
    });

    //Other listeners
}

In the above code if two connections received simultaneously the output may be (since asynchronous nature):

Received a connection
Receive a connection
Connected to server
Connected to server

But the expectation is:

Received a connection
Connected to server
Receive a connection
Connected to server

What is the proper way of ding this?

One solution is implement a queue kind of solution with emitting 'done' or 'complete' events to handle next connection.

For this we may have to take the connection callback out of the createServer call. How to handle scoping of connection and other variables (testvar) in this case?

In this case what happens to the data/messages if received on connections which are in queue but not yet processed and not yet 'data' listener is registered.?

Any other better solutions will be helpful.

Upvotes: 0

Views: 959

Answers (1)

loganfsmyth
loganfsmyth

Reputation: 161457

I think it is important to separate the concepts of synchronous code vs serial code. You want to process each request serially, but that can still be accomplished while handling each request asynchronously. For your case, the easiest way would probably be to have a queue of requests to handle instead.

var inProgress = false;
var queue = [];
net.createServer(function(sock){
    queue.push(sock);

    processQueue();
});

function processQueue(){
    if (inProgress || queue.length === 0) return;
    inProgress = true;

    handleSockSerial(queue.shift(), function(){
        inProgress = false;

        processQueue();
    });
}

function handleSockSerial(sock, callback){
    // Do all your stuff and then call 'callback' when you are done.
}

Note, as long as you are using node >= 0.10, the data coming in from the socket will be buffered until you read the data.

Upvotes: 4

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