nodejs web server and simultaneous file append - node.js

Question

I've read about nodejs event-loop, but what i don't understand well is:
i've created a simple http-server that logs the whole request post-data to a file .
i used apache-ab to flood it with a 700 kb file for-each request it does .
i imagined that each request will write some chunks after each other each tick in the event-loop, but i found that the full post data is written completely after each request and i don't know why , and i cannot understand it .
i'm using something like this
stream = require('fs').createWriteStream('path/to/log.file', {flags: 'a'})
log = function(data){
return stream.write(data)
}
require('http').createServer(function(req, res)
{
// or req.pipe(stream)
req.on('data', function(chunk){
log(chunk.toString() + "\r\n")
})
req.on('end', function(){
res.end("ok")
})
}).listen(8000)
sorry for my bad English :)

Answer 1

I edited the code to output the chunk size and also use an easily identifiable word 'SQUIRREL' to search for in the log file. I also sent the image file using curl instead of apache ab, mainly because I do not have it setup.
If you look at the output of http in the terminal you are running it, you will see the chunk size for each chunk as it is processed, which in my case was 65536 (as you alluded to in your comments we should see). In a text search, I see the word SQUIRREL one time for each chunk that was processed.
There is nothing wrong with your code, hopefully making these changes will allow you to see what you are expecting to see.
stream = require('fs').createWriteStream('./logfile.txt', {flags: 'a'});
log = function(data){
return stream.write(data);
};
require('http').createServer(function(req, res)
{
// or req.pipe(stream)
req.on('data', function(chunk){
log(chunk.toString() + "SQUIRREL ");
console.log(chunk.length);
})
req.on('end', function(){
res.end("ok");
})
}).listen(8000)
curl --data-binary "#IMAG0152.jpg" http://localhost:8000

Answer 2

thanks to everyone tried to help, i found the main issue
the stream.write was returning false i've added the following code to use drain event with .pause() and .resume() and the
problem solved
ok = stream.write(chunk)
if ( ! ok )
{
req.pause()
stream.once('drain', function(){
req.resume()
stream.write(chunk)
})
}