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javascriptnode.jssockets

Write After End error in node.js webserver

I am struggling with my node.js hobby project due to a "write after end" Error. I have a created a node.js webserver that amongst other things, sends commands received from a HTML page onwards to another process using the following code:

var netSocket = require('net').Socket();
netSocket.connect(9090);
netSocket.write(messages);
netSocket.end();

This works until the traffic starts to increase (i.e. the amount of messages being sent and or the size of the messages). At this point I get the following error: 

Error: write after end
    at writeAfterEnd (_stream_writable.js:132:12)
    at Socket.Writable.write (_stream_writable.js:180:5)
    at Socket.write (net.js:615:40)
    at Socket.<anonymous> (/Users/mark/Documents/GitHub Repos/voice_controlled_zumo/speech_module/web_server_HTTPS.js:66:15)
    at Socket.emit (events.js:95:17)
    at Socket.onevent (/Users/mark/Documents/GitHub Repos/voice_controlled_zumo/node_modules/socket.io/lib/socket.js:327:8)
    at Socket.onpacket (/Users/mark/Documents/GitHub Repos/voice_controlled_zumo/node_modules/socket.io/lib/socket.js:287:12)
    at Client.ondecoded (/Users/mark/Documents/GitHub Repos/voice_controlled_zumo/node_modules/socket.io/lib/client.js:193:14)
    at Decoder.Emitter.emit (/Users/mark/Documents/GitHub Repos/voice_controlled_zumo/node_modules/socket.io/node_modules/socket.io-parser/node_modules/component-emitter/index.js:134:20)

My guess is that the server at 9090 is being overwhelmed by the amount of traffic, giving rise to the error. As a complete newbie in the node.js world I'd really appreciate any hints for how I could resolve this issue.

Note also that the webserver is serving pages over SSL (in case that makes any difference).

Thanks for taking the time to read this!

Mark

Solution

  • NodeJS is a non-blocking async platform.

    In your case,

    netSocket.write(messages);

    is an async method; therefore, netSocket.end() is called before write is complete.

    The correct use would be:

    netSocket.write(messages, function(err) { netSocket.end(); });

    The second argument here is a callback function that will be called once the 'write' method finishes its job.

    I would recommend you read/watch more about NodeJS, async styles and callbacks.

    Here is a great place to start: https://www.youtube.com/watch?v=GJmFG4ffJZU

    And of course, the NodeJS API docs regarding net sockets.