Node.js Synchronous Readable Stream

sync-readable-stream.js

/*
Creating Synchronous Readable Stream in NodeJS
--------------------------------------------------

When data is pushed synchronously to internal buffer, you'll get the synchronous 
behaviour of the stream. This would block the rest of the code from being executed in 
the next event loop iteration.

In the example setImmediate should be called immediatley in next event loop iteration. 
But since the stream is synchronously reading data, it can't execute other callbacks.

See asynchronous version: https://gist.github.com/hassansin/77e65f2e201013dba0cb

*/
var Readable = require("stream").Readable;

function ReadStreamSync(opts){
  Readable.call(this, opts);
  this._max = 1000000;
  this._index = 1;
}
require("util").inherits(ReadStreamSync, Readable)

ReadStreamSync.prototype._read = function(n) {
  var i = this._index++;
  if (i > this._max)
    this.push(null);
  else {
    var str = '' + i;
    var buf = new Buffer(str, 'ascii');
    
    //synchronously pushing data in buffer
    this.push(buf);
  }
};

console.log(new Date().toTimeString() ,"Start")
var readable = new ReadStreamSync();

//reading starts from next tick
readable.on('data', function(chunk) {   
    //do stuff
});
readable.on('end', function(){
  console.log(new Date().toTimeString() ,'Done');
});

//scheduled to run on next tick
setImmediate(function(){
  console.log(new Date().toTimeString() ,'setImmediate')
})


/*
Output:
---------------

14:41:57 GMT+0000 (UTC) Start
14:41:59 GMT+0000 (UTC) Done
14:41:59 GMT+0000 (UTC) setImmediate

*/