Exploring a node.js memory leak with sending files and setting the Content-Length header

server.js

var fs   = require('fs');
var http = require('http');
var file = __dirname + '/index.html';
var connections = {};
var idCouner = 0
var port = 8080;

var handleRequset = function(request, response){
  idCouner++
  var id = idCouner;
  connections[id] = {req: request, res: response};

  response.on('finish', function(){
    delete connections[id];
  });

  fs.stat(file, function(error, stats){
    if(error){ throw error;  }
    response.writeHead(200, [['Content-Length', stats.size]]);

    var fileStream = fs.createReadStream(file);
    fileStream.on('open', function(){
      fileStream.pipe(response);
    });

    fileStream.on('error', function(error){
      console.log(error); // no errors are caught
    });
  });
};

http.createServer(handleRequset).listen(port);

console.log('server running on port ' + port);
setInterval(function(){
  console.log('connections: ' + Object.keys(connections));
}, 5000);

Sometimes fs.createReadStream never finishes

Or maybe it doesn't always propagate to the next stream?

Run the server node server.js, and hit it hard with the loadtest package.

• npm install loadtest
• ./node_modules/.bin/loadtest -c 10 --rps 200 http://localhost:8080

If let run long enough, the count of un-finished connections will grow linearly with time:

> node server
server running on port 8080
connections: 0
connections: 0
connections: 2
connections: 2
connections: 2
connections: 4
connections: 4
connections: 4
connections: 5
connections: 6
connections: 6
connections: 6
connections: 6
connections: 6
connections: 7
connections: 9
connections: 9
connections: 9
connections: 9
connections: 11
connections: 9
connections: 11
connections: 12
...

This seems to indicate that there is a small problem < ~1% of the time, where the finished event isn't emitted. If you remove line 15, everything is fine, and the number of un-finished connections stays low and constant. How does sending the Content-Length header modify the request behavior?

Help?

I confirmed this on Node 4.2.3 and 6.2.0 (using NVM). I can also confirm that removing the "Content-Length" writeHead line eliminates the problem.

I've modified the code a bit to give each connection and ID, and return those IDs every 5 seconds so we can prove that the same connections are in fact 'stuck' in an un-finished state.

> node server.js
server running on port 8080
connections:
connections: 2867
connections: 2867
connections: 2867
connections: 2867
connections: 2867
connections: 2867
connections: 2867
connections: 2867
connections: 2867
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403
connections: 2867,12403,22350
connections: 2867,12403,22350

Confirmed on Node 4.2.4 (Windows 7):

λ node server.js
server running on port 8081
connections: 19,20,21,63,103,105,114,124,197,847,853,1046,1105
connections: 19,20,21,63,103,105,114,124,197,847,853,1046,1105,1210,1266,1290,1297,1583,1714,2047,2203
connections: 19,20,21,63,103,105,114,124,197,847,853,1046,1105,1210,1266,1290,1297,1583,1714,2047,2210,2234,2413,2542,2657,2706,2708,2709,3205
connections: 19,20,21,63,103,105,114,124,197,847,853,1046,1105,1210,1266,1290,1297,1583,1714,2047,2210,2234,2413,2542,2657,2706,2708,2709,3275,3346,3523,3525
connections: 19,20,21,63,103,105,114,124,197,847,853,1046,1105,1210,1266,1290,1297,1583,1714,2047,2210,2234,2413,2542,2657,2706,2708,2709,3275,3346,3523,3525,4269
connections: 19,20,21,63,103,105,114,124,197,847,853,1046,1105,1210,1266,1290,1297,1583,1714,2047,2210,2234,2413,2542,2657,2706,2708,2709,3275,3346,3523,3525,4269,5416,5783,5784,5865,6147,6148
connections: 19,20,21,63,103,105,114,124,197,847,853,1046,1105,1210,1266,1290,1297,1583,1714,2047,2210,2234,2413,2542,2657,2706,2708,2709,3275,3346,3523,3525,4269,5416,5783,5784,5865,6147,6148,6563,6779,7139,7140
connections: 19,20,21,63,103,105,114,124,197,847,853,1046,1105,1210,1266,1290,1297,1583,1714,2047,2210,2234,2413,2542,2657,2706,2708,2709,3275,3346,3523,3525,4269,5416,5783,5784,5865,6147,6148,6563,6779,7139,7140,7318,8214

Please move conversation about this issue to nodejs/node#6929