Emulate server in Node.js - stream delimited file with 1-second pauses - node.js

Question

I'm new to Node.js and I am writing a client to consume a text-based TCP stream from a server. For testing purposes, I want to simulate the server in Node so I can test with no other dependencies.
I have a file of captured data that looks like:
$X,... <-- broadcast every second
$A,...
$A,...
$B,...
$X,... <-- broadcast every second
$A,...
$A,...
$C,...
$X,... <-- broadcast every second
The server emits a line starting with $X every second. The other records are broadcast as events happen. How can I modify my network server below to broadcast this data and throttle it so it emits one line at a time and pauses for one second every time it encounters a line starting with $X?
Here is my code so far which reads in the data and broadcasts it over a port:
var http = require('http')
, fs = require('fs')
;
var server = http.createServer(function (req, res) {
var stream = fs.createReadStream(__dirname + '/data.txt');
stream.pipe(res);
});
server.listen(8000);
console.log('server running on 8000');
This works but obviously just streams out the whole file at warp speed. What I want is to spit out all of the lines from one $X to the next, pause for one second (close enough for testing purposes) and then continue to the next $X and so on like:
> telnet 127.0.0.1 8000
$X,...
$A,...
$A,...
$B,...
(output would pause for one second)
$X,...
$A,...
$A,...
$C,...
(output would pause for one second)
$X,...
...
In my example above, the broadcast always starts from the beginning of data.txt when I connect with a client. Ideally, this server would keep broadcasting this data in a loop, allowing clients to disconnect and reconnect at any time and start receiving data wherever the server simulator was currently at.
(PS - data.txt is a relatively small file, < 1MB in most cases)
UPDATE -
Thanks to Laurent's pointer, I was able to get it working with the following:
var net = require('net'),
fs = require('fs'),
async = require('async');
var server = net.createServer(function (socket) {
var lines = fs.readFileSync(__dirname + '/data-small.txt').toString().split(/\n+/);
async.whilst(
function () {
return lines.length > 0;
},
function (done) {
var line = lines.shift();
socket.write(line + '\r\n');
setTimeout(done, /^\$X,/.test(line) ? 1000 : 0);
},
function (err) {
// no more lines present
socket.end();
});
});
server.listen(8000);
console.log('server running on 8000');
I'm now getting a blast of lines until an $X, a 1s pause, and then it continues! Thanks!
Drilling into my 2nd part: is there a way to synchronize output of this faux server so all clients see the same output regardless of when they connect?

Answer 1

If you want to keep all clients in sync, you need to do something entirely different. Here's a starting point. Also, it seems like the net module would be a better fit.
var net = require('net'),
fs = require('fs'),
_ = require('underscore');
var current = 0,
sockets = [];
// dirty parser for blocs
var data = fs.readFileSync(__dirname + '/data.txt').toString(),
blocs = _.chain(data.split(/\$X,/)).compact().map(function (bloc) {
return '$X,' + bloc;
}).value();
function streamBloc() {
console.log('writing bloc #' + current + ' to ' + sockets.length + ' sockets');
_(sockets).each(function (socket) {
socket.write(blocs[current]);
});
current = (current + 1) % blocs.length;
setTimeout(streamBloc, 1000);
}
var server = net.createServer(function (socket) {
console.log('incoming connection');
// immediately write current bloc
socket.write(blocs[current]);
// add to sockets so that it receive future blocs
sockets.push(socket);
// cleanup when the client leaves
socket.on('end', function () {
sockets = _(sockets).without(socket);
});
}).listen(8000, function () {
console.log('server listening on port 8000');
});
streamBloc();