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.
E.g
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.
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
});
It's hard to say without knowing what protocol you are speaking with the modem, but if it's e.g. \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(''));
});
Related
I have two PCM-streams (decoder1 + decoder2):
var readable1 = fs.createReadStream("track1.mp3");
var decoder1 = new lame.Decoder({
channels: 2,
mode: lame.STEREO
});
readable1.pipe(decoder1);
and
var readable2 = fs.createReadStream("track2.mp3");
var decoder2 = new lame.Decoder({
channels: 2,
mode: lame.STEREO
});
readable2.pipe(decoder2);
Now I want to pipe the streams into one mix-function, where I can use the buffer-function like:
function mixStream(buf1, buf2, callback) {
// The mixStream-Function is not implemented yet (dummy)
var out = new Buffer(buf1.length);
for (i = 0; i < buf1.length; i+=2) {
var uint = Math.floor(.5 * buf1.readInt16LE(i));
out.writeInt16LE(uint, i);
}
this.push(out);
callback();
}
I need something like
mixStream(decoder1.pipe(), decoder2.pipe(), function() { }).pipe(new Speaker());
for output to speaker. Is this possible?
Well, pipe() function actually means a stream is linked to another, a readable to a writable, for instance. This 'linking' process is to write() to the writable stream once any data chunk is ready on the readable stream, along with a little more complex logic like pause() and resume(), to deal with the backpressure.
So all you have to do is to create a pipe-like function, to process two readable streams at the same time, which drains data from stream1 and stream2, and once the data is ready, write them to the destination writable stream.
I'd strongly recommend you to go through Node.js docs for Stream.
Hope this is what you are looking for :)
I am pretty new to Node.Js and I'm using tcp sockets to communicate with a client. Since the received data is fragmented I noticed that it prints "ondata" to the console more than once. I need to be able to read all the data and concatenate it in order to implement the other functions. I read the following http://blog.nodejs.org/2012/12/20/streams2/ and thought I can use socket.on('end',...) for this purpose. But it never prints "end" to the console.
Here is my code:
Client.prototype.send = function send(req, cb) {
var self = this;
var buffer = protocol.encodeRequest(req);
var header = new Buffer(16);
var packet = Buffer.concat([ header, buffer ], 16 + buffer.length);
function cleanup() {
self.socket.removeListener('data', ondata);
self.socket.removeListener('error', onerror);
}
var body = '';
function ondata() {
var chunk = this.read() || '';
body += chunk;
console.log('ondata');
}
self.socket.on('readable', ondata);
self.socket.on('end', function() {
console.log('end');
});
function onerror(err) {
cleanup();
cb(err);
}
self.socket.on('error', onerror);
self.socket.write(packet);
};
The end event will handle the FIN package of the TCP protocol (in other words: will handle the close package)
Event: 'end'#
Emitted when the other end of the socket sends a FIN packet.
By default (allowHalfOpen == false) the socket will destroy its file descriptor once it has written out its pending write queue. However, by setting allowHalfOpen == true the socket will not automatically end() its side allowing the user to write arbitrary amounts of data, with the caveat that the user is required to end() their side now.
About FIN package: https://en.wikipedia.org/wiki/Transmission_Control_Protocol#Connection_termination
The solution
I understand your problem, the network communication have some data transfer gaps and it split your message in some packages. You just want read your fully content.
For solve this problem i will recommend you create a protocol. Just send a number with the size of your message before and while the size of your concatenated message was less than total of your message size, keep concatenating :)
I have created a lib yesterday to simplify that issue: https://www.npmjs.com/package/node-easysocket
I hope it helps :)
I am using node.js and reading input from a serial port by opening a /dev/tty file, I send a command and read the result of the command and I want to close the stream once I've read and parsed all the data. I know that I'm done reading data by and end of data marker. I'm finding that once I've closed the stream my program does not terminate.
Below is an example of what I am seeing but uses /dev/random to slowly generate data (assuming your system isn't doing much). What I find is that the process will terminate once the device generates data after the stream has been closed.
var util = require('util'),
PassThrough = require('stream').PassThrough,
fs = require('fs');
// If the system is not doing enough to fill the entropy pool
// /dev/random will not return much data. Feed the entropy pool with :
// ssh <host> 'cat /dev/urandom' > /dev/urandom
var readStream = fs.createReadStream('/dev/random');
var pt = new PassThrough();
pt.on('data', function (data) {
console.log(data)
console.log('closing');
readStream.close(); //expect the process to terminate immediately
});
readStream.pipe(pt);
Update:1
I am back on this issue and have another sample, this one just uses a pty and is easily reproduced in the node repl. Login on 2 terminals and use the pty of the terminal you're not running node in the below call to createReadStream.
var fs = require('fs');
var rs = fs.createReadStream('/dev/pts/1'); // a pty that is allocated in another terminal by my user
//wait just a second, don't copy and paste everything at once
process.exit(0);
at this point node will just hang and not exit. This is on 10.28.
Instead of using
readStream.close(),
try using
readStream.pause().
But, if you are using the newest version of node, wrap the readstream with the object created from stream module by isaacs, like this :
var Readable = require('stream').Readable;
var myReader = new Readable().wrap(readStream);
and use myReader in place of readStream after that.
Best of luck! Tell me if this works.
You are closing the /dev/random stream, but you still have a listener for the 'data' event on the pass-through, which will keep the app running until the pass-through is closed.
I'm guessing there is some buffered data from the read stream and until that is flushed the pass-through is not closed. But this is just a guess.
To get the desired behaviour you can remove the event listener on the pass-through like this:
pt.on('data', function (data) {
console.log(data)
console.log('closing');
pt.removeAllListeners('data');
readStream.close();
});
i am actually pipe to a http request.. so for me it's about :
pt.on('close', (chunk) => {
req.abort();
});
I'm attempting to create a Readable file stream that I can read individual bytes from. I'm using the code below.
var rs = fs.createReadStream(file).on('open', function() {
var buff = rs.read(8); //Read first 8 bytes
console.log(buff);
});
Given that file is an existing file of at least 8 bytes, why am I getting 'null' as the output for this?
Event open means that stream has been initialized, it does not mean you can read from the stream. You would have to listen for either readable or data events.
var rs = fs.createReadStream(file);
rs.once('readable', function() {
var buff = rs.read(8); //Read first 8 bytes only once
console.log(buff.toString());
});
It looks like you're calling this rs.read() method. However, that method is only available in the Streams interface. In the Streams interface, you're looking for the 'data' event and not the 'open' event.
That stated, the docs actually recommend against doing this. Instead you should probably be handling chunks at a time if you want to stream them:
var rs = fs.createReadStream('test.txt');
rs.on('data', function(chunk) {
console.log(chunk);
});
If you want to read just a specific portion of a file, you may want to look at fs.open() and fs.read() which are lower level.
I am trying to learn about streams in node.js!
server.js
var net = require("net");
var server = net.createServer(function(conn) {
conn.write("welcome!");
# echo the user input!
conn.pipe(conn);
});
server.listen("1111", function() {
console.log("port 1111 opened");
});
telnet test
The server currently echos the user's input
$ telnet localhost 1111
welcome!
hello
hello
desired output
To demonstrate where/how I should process the stream on the server side, I would like to wrap the user's input in {} before echoing it back
$ telnet localhost 1111
welcome!
hello
{hello}
This will basically accomplish the exact output you've requested:
var net = require('net');
var server = net.createServer(function(c) {
c.setEncoding('utf8');
c.on('data', function(d) {
c.write('{' + d.trim() + '}\n');
});
});
server.listen(9871);
First let me call your attention to c.setEncoding('utf8'). This will set a flag on the connection that will automatically convert the incoming Buffer to a String in the utf8 space. This works well for your example, but just note that for improved performance between Sockets it would be better to perform Buffer manipulations.
Simulating the entirety of .pipe() will take a bit more code.
.pipe() is a method of the Stream prototype, which can be found in lib/stream.js. If you take a look at the file you'll see quite a bit more code than what I've shown above. For demonstration, here's an excerpt:
function ondata(chunk) {
if (dest.writable) {
if (false === dest.write(chunk) && source.pause) {
source.pause();
}
}
}
source.on('data', ondata);
First a check is made if the destination is writable. If not, then there is no reason to attempt writing the data. Next the check if dest.write === false. From the documentation:
[.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.
Since Streams live in kernel space, outside of the v8 memory space, it is possible to crash your machine by filling up memory (instead of just crashing the node app). So checking if the message has drained is a safety prevention mechanism. If it hasn't finished draining, then the source will be paused until the drain event is emitted. Here is the drain event:
function ondrain() {
if (source.readable && source.resume) {
source.resume();
}
}
dest.on('drain', ondrain);
Now there is a lot more we could cover with how .pipe() handles errors, cleans up its own event emitters, etc. but I think we've covered the basics.
Note: When sending a large string, it is possible that it will be sent in multiple packets. For this reason it may be necessary to do something like the following:
var net = require('net');
var server = net.createServer(function(c) {
var tmp = '';
c.setEncoding('utf8');
c.on('data', function(d) {
if (d.charCodeAt(d.length - 1) !== 10) {
tmp += d;
} else {
c.write('{' + tmp + d.trim() + '}\n');
tmp = '';
}
});
});
server.listen(9871);
Here we use the assumption that the string is ended by the new line character (\n, or ascii character code 10). We check the end of the message to see if this is the case. If not, then we temporarily store the message from the connection until the new line character is received.
This may not be a problem for your application, but thought it would be worth noting.
you can do something like
conn.on 'data', (d) ->
conn.write "{#{d}}"
the .pipe method is basically just attaching the data event of the input stream to write to the output stream
I'm not sure about net() actually, but I imagine it's quite similar to http:
http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/event-stream'});
http.get(options, function(resp){
resp.on('data', function(chunk){
res.write("event: meetup\n");
res.write("data: "+chunk.toString()+"\n\n");
});
}).on("error", function(e){
console.log("Got error: " + e.message);
});
});
https://github.com/chovy/nodejs-stream