fs does not Write all received data file

Question

fs does not Write all received data file

My node.js script:

var net = require('net');
var fs = require('fs');

var client = new net.Socket()

client.connect(PORT, HOST, function () {
       client.write('You can Send file\0');
       client.on('data', function (data) {
            // console.log(data); 
            var destinationFile = fs.createWriteStream("destination.txt");
            destinationFile.write(data);
       });  
 });

it is coded for receiving a file from remote HOST. when i use console.log(data) its OK to log remote data file to console. but for writing data to file its write one part of received data file. How can write all data to file? thanks

node.js
sockets
filestream

Answer 1

The cause of what you get:

client.on('data') is called multiple times, as the file is being sent in data-chunks, not as a single whole data. As a result on receiving each piece of data, you create a new file stream and write to it..

Console.log on the other hand works, because it does not create new console window each time you write to it.

Quick solution would be:

client.connect(PORT, HOST, function () {
       var destinationFile = fs.createWriteStream("destination.txt");
       client.write('You can Send file\0');
       client.on('data', function (data) {
            // console.log(data); 
            destinationFile.write(data);
       });  
 });

Also notice in the net Documentation on net.connect method:

Normally this method is not needed, as net.createConnection opens the socket. Use this only if you are implementing a custom Socket.

Answer 2

The problem you got is because you declare the filestream inside the event on, which is called each time a packet arrive.

client.connect(PORT, HOST, function () {
    var destinationFile = fs.createWriteStream("destination.txt"); //Should be here
    client.write('You can Send file\0');
    client.on('data', function (data) {
        destinationFile.write(data);
    });  
 });

thanks. in tiny test its OK. but written file has 16 bit more than real size. first of file has 16 bit of unknown data. how to ignore that?

In your code, since client.on is called multiple time, multiple write happens in the same times, so it is undefined behavior for which write happens, in which order, or if they ll be complete.

The 16 bytes of unknown data are probably bytes from different packet writen one after the other in random order. Your tiny test work because the file can be send in one packet, so the event is called only once.

If you declare the filestream first, then call the write in client.on, the order of write and data are preserved, and the file is written successfully.