Write After End error in node.js webserver

Question

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

Answer 1

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.