Output breaking in child Process by nodejs

Question

I connected wavecom GSM modem on ubantu. I use node.js language to communicate with GSM modem. I send command to modem by Child Process . Here example

var spawn         = require("child_process").spawn,
    exec          = require('child_process').exec;

 // Write dev_ttyUSB15.tmp file
 var child = exec('cat < /dev/ttyUSB15 > /tmp/dev_ttyUSB15.tmp');

 // Read dev_ttyUSB15.tmp file
 var m1 = spawn('tail',['-f','/tmp/dev_ttyUSB15.tmp']);

 // on data event is emitted when dev_ttyUSB15.tmp file has some data 
 m1.stdout.on('data', function (data) {
     console.log("Data : "+data); // this is executed as output
 });

Now When I fire some command on port /dev/ttyUSB15 I do not get output properly.

Eg

Suppose my output should be

Data : abcd1234

but instead of it I got

Data : abc
Data : d1234

In short My output is breaked. I can not extrapolate from where my output exactly break. It's random. Can anyone give me any idea?

Thanks in advance.

Answer 1

It's hard to say without knowing what protocol you are speaking with the modem, but if it's eg \\n delimited, you will have to buffer the data and split on \\n :

var buffer = '';
m1.stdout.on('data', function(data) {
    var received = (buffer + data).split('\n');
    buffer = received.pop().trim();
    console.log(received.join(''));
});

Answer 2

As all streams in node.js, the reading of data consists of 2 separate events: data and end .

data event is fired when some data is readable in the stream (in your case, twice).

end event is fired when no more data events will be fired.

var blob = "";
m1.stdout.on('data', function (data) {
 blob += data;
});

m1.stdout.on('end', function () {
 console.log("Data : " + blob); // here you have all the data within one variable
});