CODEWITHSUNDEEP
node.jssockets
Andrew Chambers
Andrew Chambers

Reputation: 83

nodejs socket write ordering

When writing a nodejs proxy server I noticed that data may come into my proxy many times before the data is written to the other socket end. each time my data comes in, i call socket.write(); ...

However I am unsure if the order of the data being transmitted is guaranteed by nodejs to be the same as the order i scheduled the writes due to the asynchronous nature of the sending.

Does anyone know the behavior of nodejs in this situation?

If the order is not guaranteed, then i will have to buffer the data until i recieve the data successfully sent callback.

Upvotes: 4

Views: 3470

Answers (1)

AndyD
AndyD

Reputation: 5385

Node.js is single threaded and can only ever do one thing at a time. It has a queue of callbacks that get processed in order. some more information can be found here: http://howtonode.org/understanding-process-next-tick.

As long as you are calling socket.write when you receive data then it will arrive in order. If you think about it, if it didn't do this then node would not be usable as a webserver. For example, a simple node express site might use fs.readfile to read a file from disc asynchronously and serve it back to the browser using socket.write. If the order was not guaranteed, that file might not be returned correctly.

From the node 0.8.14 documentation: http://nodemanual.org/latest/nodejs_ref_guide/net.html#net.Socket.write

Returns true if the entire data was flushed successfully to the kernel buffer. Returns false if all or part of the data was queued in user memory. 'drain' is emitted when the buffer is again free.

and

net.Socket has the property that socket.write() always works. This is to help users get up and running quickly. The computer can't always keep up with the amount of data that is written to a socket—the network connection simply might be too slow. Node.js will internally queue up the data written to a socket and send it out over the wire whenever it's possible. (Internally, it's polling on the socket's file descriptor for being writable.)

Upvotes: 5

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