Hooking into Node.js stdout, pipe stdout to telnet

intercept-stdout.js

var _ = require('underscore'),
    util = require('util');

// intercept stdout, passes thru callback
// also pass console.error thru stdout so it goes to callback too
// (stdout.write and stderr.write are both refs to the same stream.write function)
// returns an unhook() function, call when done intercepting
module.exports = function interceptStdout(callback) {
  var old_stdout_write = process.stdout.write,
      old_console_error = console.error;

  process.stdout.write = (function(write) {
    return function(string, encoding, fd) {
      var args = _.toArray(arguments);
      write.apply(process.stdout, args);

      // only intercept the string
      callback.call(callback, string);
    };
  }(process.stdout.write));

  console.error = (function(log) {
    return function() {
      var args = _.toArray(arguments);
      args.unshift('[ERROR]');
      console.log.apply(console.log, args);
      
      // string here encapsulates all the args
      callback.call(callback, util.format(args));
    };
  }(console.error));

  // puts back to original
  return function unhook() {
    process.stdout.write = old_stdout_write;
    console.error = old_console_error;
  };
};

pipe stdout to telnet socket

  var server = require('net').createServer();

  server.listen(5000, function() {
    console.log('Telnet server running on port', server.address().port);
  });

  server.on('connection', function(socket) {
    // pipe logs to telnet for the duration of connection
    var unhookStdout = require('./intercept-stdout')(function intercept(string){
      socket.write(string);
    });
    
    console.log('is this going to telnet?');

    socket.on('end', function(){
      unhookStdout();
    });

    socket.on('data', function(data) {
      socket.setEncoding('utf8');

      // should only be 1 line at a time
      data = data.toString().replace(/(\r\n|\n|\r)/gm,"");

      switch(data) {
        case 'quit':
          socket.write('Goodbye.\n');
          socket.end();
          break;

        case 'test':
          setInterval(function() { console.log(Date()); }, 500);

          break;

        default:
          socket.write('\nUnknown command: ' + data + '\n');
      }
    });
  });

test-intercept.js

// test intercept w/ terminal

var _ = require('underscore'),
    util = require('util');

// to stdout
console.log('a', 1, {a:'b'});
console.log('b', 1, {a:'b'});

util.debug('intercept on');

var unhook = require('./intercept-stdout')(function intercept(){
  var args = _.toArray(arguments);
  util.debug.apply(this, args);
});

// intercepted
console.log('c', 1, {a:'b'});
console.log('d', 1, {a:'b'});

console.error('error e', 1, {a:'b'});

// back to stdout
unhook();
util.debug('Unhooked');

console.log('f back', 1, {a:'b'});
console.error('g error back', 1, {a:'b'});

This is exactly what I was looking for. I have been trying to get mocha's reporters to output to a specified file using Gulp, but mocha does not have any interface for doing this, as the Reporters simply use process.stdout.write() for output. Using this gist I am able to put reports where I want them without having to mess around with any of the core mocha files.

Thanks for posting!

thanks for posting. saved me heaps of time

Rock on wit'cho bad self. Similarly to glosee, I'm trying to log mocha out to file. This'll work!

Cheers!