在nodejs和Python之间交换数据

Question

I am new to node and socket.io. I have a nodejs server that I am trying to use to both spawn a Python process from, and pass data to and from a web page. On the Python end I'm trying to use Python's stdin/stdout pipes.

Everything coming from Python to nodejs and on to the server works fine. However, when I attempt to pass data from nodejs back to Python using stdin.write, node crashes with a "write after end" error. I am wondering if the socket I'm using to receive from Python is conflicting with that I'm trying to send back. I am using a timer to send data to the web page every second.

This seems to have something to do with Python expecting an EOF when calling sys.stdin.readlines(), however, when I use stdin.end() from nodejs, that's when I get the error. Interestingly, if I never call stdin.end, I don't get the error, but I also don't receive anything.

Any help is greatly appreciated. I'm afraid I don't know enough about socket.io to see what's going wrong here. Thank you.

IN NODEJS: Spawning the Python process:

var util = require('util'),
spawn = require('child_process').spawn,
py = spawn('python', ['data_collect.py']);

Receiving data from Python:

py.stdout.on('data', function(data){
    python_output = data.toString();

Sending data to Browser:

var listener = io.listen(server);
listener.sockets.on('connection', function (socket) {
    socket.emit( 'dataPacket1', {variable_1: data1});
    socket.emit( 'dataPacket2', {variable_2: data2});
    socket.emit( 'dataPacket3', {variable_3: data3});
}, 1000); 

Receiving from browser and sending to Python:

socket.on('messageFromBrowser', function(data) {
    py.stdin.setEncoding('utf-8');
    py.stdin.write(JSON.stringify(data.browser_value+'\n'));
    py.stdin.end();   <--- Error happens here

});

IN PYTHON: Sending to nodejs:

output = "dataout"
sys.stdout.write(output)
sys.stdout.flush() 

Receiving from nodejs:

lines = []

while True:
    line = sys.stdin.readline()
    if line !='':
        lines.append(line)
    else:
        break
return lines

Answer 1

if you want to combine node and python I think the best solution is to move to a microservice architecture using Seneca.JS. If I was in you I will create a rest interface to communicate between the a python process and node.js microservice. you can find more information here

Answer 2

Remove the py.stdin.end(). And make sure '\\n' is outside stringify

py.stdin.write(JSON.stringify(data.browser_value)+'\n');