node.js: How to detect an empty stdin stream?

Question

I have a node.js script/server that reads some input from stdin when its launched. However, sometimes there's no data to be passed in. This is troublesome because it seems like in this case neither the data nor end events are called. How can I detect when this is the case in the node.js code?

I'd like to avoid having to append special "end" characters at the end of the input, so as not to inconvenience the client. The associated code is below:

  var newHTML = '';
  var gfm = spawn(__dirname + '/node_modules/docter/bin/github-flavored-markdown.rb');
  process.stdin.on('data', function(chunk){
    gfm.stdin.write(chunk);
  });
  process.stdin.on('end', function(){
    gfm.stdin.end();
  });
  gfm.stdout.on('data', function(data) {
    newHTML += data;
  });
  gfm.on('exit',function(ecode){
    socket.emit('newContent', newHTML);
  });
  process.stdin.resume();

Answer 1

An empty or no STDIN stream is detected by the end event from process.stdin.

This simple script stdin.js demonstrates that:

process.stdin.on( 'data', function(data) { console.log( data ) } );
process.stdin.on( 'end', function() { console.log( 'EOF' ) } );

Different scenarios:

$ echo test | node stdin.js
<Buffer 74 65 73 74 0a>
EOF
$ echo -n | node stdin.js
EOF
$ node stdin.js < /dev/null
EOF
$

This script pipe.js demonstrates that using pipe to a spawned child process works very well:

var spawn = require('child_process').spawn;
var cat = spawn( '/bin/cat' );
cat.stdout.on( 'data', function(data) { console.log( data ) } );
cat.stdout.on( 'end', function() { console.log( 'EOF' ) } );

process.stdin.pipe(cat.stdin);

As expected:

$ echo test | node pipe.js
<Buffer 74 65 73 74 0a>
EOF
$ echo -n | node pipe.js
EOF
$ node pipe.js < /dev/null
EOF
$

Answer 2

I believe what may be happening is, you are not giving a stdin steam at all.

Øystein Steimler's example shows you feeding /dev/null into your app:

node pipe.js < /dev/null

However, never addressed when you do not stream stdin to the app at all. Just running node pipe.js will not exit because it is still waiting for stdin.

You can test this yourself with other unix programs, for example cat

Try running this:

cat < /dev/null

Now try just running:

cat

It does not exit because it is waiting for stdin. You can type into the terminal and send to the program by pressing enter. It will still not exit (and wait for more input) until it receives the EOF which you can do with ctrl+d