[Node.js] Level 3 new. Steam

File Read Stream

Lets use the fs module to read a file and log its contents to the console.

Use the fs module to create a Readable stream for fruits.txt. Store the new stream in a variable called file.

fs.createReadStream('fruits.txt');

Next, listen to the readable event on the newly created stream and give it a callback.

file.on('readable', function(){});

Inside the callback, read the data chunks from the stream and print them to the console using console.log() - you might want to use a while loop to do this. Don't forget to call toString() on the data before printing it.

file.on('readable', function(){
  while(null !== (chunk = file.read())){
      console.log(chunk.toString());
  }
});

var fs = require('fs');
var file = fs.createReadStream('fruits.txt');

file.on('readable', function(){
  while(null !== (chunk = file.read())){
      console.log(chunk.toString());
  }
});

File Piping

Instead of manually listening for the 'readable' event on theReadable stream, let's use pipe to read from the stream and write directly to process.stdout.

Start by removing the code for the readable handler.

Call file.pipe(), passing it the stream to write to.

var file = fs.createReadStream('fruits.txt');
file.pipe(process.stdout);

Read More: http://nodejs.org/api/stream.html#stream_readable_pipe_destination_options

For example, emulating the Unix cat command:

process.stdin.pipe(process.stdout);

var fs = require('fs');

var file = fs.createReadStream('fruits.txt');
file.pipe(process.stdout);

Fixing Pipe

The following code will throw an error because pipe automatically closed our writable stream.

You'll need to consult the pipe documentation to figure out the option which keeps the Write stream open and dispatches the end event.

　　By default end() is called on the destination when the source stream emits end, so that destination is no longer writable. Pass{ end: 　　false } as options to keep the destination stream open.

file.pipe(destFile, { end: false });

var fs = require('fs');

var file = fs.createReadStream('origin.txt');
var destFile = fs.createWriteStream('destination.txt');

file.pipe(destFile, { end: false });

file.on('end', function(){
  destFile.end('Finished!');
});

Download Server

Let's create an HTTP server that will serve index.html.

Use pipe() to send index.html to the response.

var fs = require('fs');
var http = require('http');

http.createServer(function(request, response) {
  response.writeHead(200, {'Content-Type': 'text/html'});

  var file = fs.createReadStream('index.html');
  file.pipe(response);
}).listen(8080);