Not receiving stdout from nodejs spawned process

Question

I\'m trying to have nodejs interact with adventure, an old text based game. The idea is to open adventure as a child process and then play the game by writing

Answer 1

Why isn't that initial line from the game being picked up?

I had the same problem on a project that called a compiled C++ program from node.js. I realized the problem was in the compiled C++ program: I wasn't flushing the stdout stream. Adding fflush(stdout); after printing a line solved the issue. Hopefully you still have access to the source of the game!

Answer 2

The data passed is a buffer type, not a string. Therefore, you need a decoder to read that buffer and then do the logging.

Here's how to do that.

var StringDecoder = require('string_decoder').StringDecoder;
var decoder = new StringDecoder('utf8');

child.stdout.on('data', function (data) {
    var message = decoder.write(data);
    console.log(message.trim());
});

Answer 3

After going through the Nodejs documentation a few more times, I convinced myself I was either missing something pretty big, or the spawn command wasn't working correctly. So I created a github issue.

And the answer was immediately posted: the child process can't buffer output if you want fast access.

So to achieve what I was originally looking for:

var childProcess = require('child_process');
var spawn = childProcess.spawn;
var child = spawn('unbuffer', 'adventure');

console.log("spawned: " + child.pid);

child.stdout.on('data', function(data) {
  console.log("Child data: " + data);
});
child.on('error', function () {
  console.log("Failed to start child.");
});
child.on('close', function (code) {
  console.log('Child process exited with code ' + code);
});
child.stdout.on('end', function () {
  console.log('Finished collecting data chunks.');
});

With the functional difference being the use of unbuffer, a command that disables output buffering.