http: Optimize queued client aborts

Avoid sending unsent data and destroying otherwise legitimate sockets
for requests that are aborted while still in the agent queue. This
reduces stress on upstream systems who will likely respond to the
request but client app already knows that it will be dropped on the
floor and also helps avoid killing keep-alive connections.

lib/_http_client.js

@@ -174,6 +174,8 @@ util.inherits(ClientRequest, OutgoingMessage);
 
 exports.ClientRequest = ClientRequest;
 
+ClientRequest.prototype.aborted = undefined;
+
 ClientRequest.prototype._finish = function() {
   DTRACE_HTTP_CLIENT_REQUEST(this, this.connection);
   COUNTER_HTTP_CLIENT_REQUEST();
@@ -186,6 +188,11 @@ ClientRequest.prototype._implicitHeader = function() {
 };
 
 ClientRequest.prototype.abort = function() {
+  // Mark as aborting so we can avoid sending queued request data
+  // This is used as a truthy flag elsewhere. The use of Date.now is for debugging
+  // purposes only.
+  this.aborted = Date.now();
+
   // If we're aborting, we don't care about any more response data.
   if (this.res)
     this.res._dump();
@@ -194,14 +201,11 @@ ClientRequest.prototype.abort = function() {
       res._dump();
     });
 
+  // In the event that we don't have a socket, we will pop out of
+  // the request queue through handling in onSocket.
   if (this.socket) {
     // in-progress
     this.socket.destroy();
-  } else {
-    // haven't been assigned a socket yet.
-    // this could be more efficient, it could
-    // remove itself from the pending requests
-    this._deferToConnect('destroy', []);
   }
 };
 
@@ -485,7 +489,12 @@ ClientRequest.prototype.onSocket = function(socket) {
   var req = this;
 
   process.nextTick(function() {
-    tickOnSocket(req, socket);
+    if (req.aborted) {
+      // If we were aborted while waiting for a socket, skip the whole thing.
+      socket.emit('free');
+    } else {
+      tickOnSocket(req, socket);
+    }
   });
 };
 

test/simple/test-http-abort-queued.js

@@ -0,0 +1,103 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var assert = require('assert'),
+    http = require('http');
+
+var complete;
+
+var server = http.createServer(function (req, res) {
+  // We should not see the queued /thatotherone request within the server
+  // as it should be aborted before it is sent.
+  assert.equal(req.url, '/');
+
+  res.writeHead(200);
+  res.write('foo');
+
+  complete = complete || function () {
+    res.end();
+  };
+});
+
+
+server.listen(0, function () {
+  console.log('listen', server.address().port);
+
+  var agent = new http.Agent({maxSockets: 1});
+  assert.equal(Object.keys(agent.sockets).length, 0);
+
+  var options = {
+    hostname: 'localhost',
+    port: server.address().port,
+    method: 'GET',
+    path: '/',
+    agent: agent
+  };
+
+  var req1 = http.request(options);
+  req1.on('response', function(res1) {
+    assert.equal(Object.keys(agent.sockets).length, 1);
+    assert.equal(Object.keys(agent.requests).length, 0);
+
+    var req2 = http.request({
+      method: 'GET',
+      host: 'localhost',
+      port: server.address().port,
+      path: '/thatotherone',
+      agent: agent
+    });
+    assert.equal(Object.keys(agent.sockets).length, 1);
+    assert.equal(Object.keys(agent.requests).length, 1);
+
+    req2.on('error', function(err) {
+      // This is expected in response to our explicit abort call
+      assert.equal(err.code, 'ECONNRESET');
+    });
+
+    req2.end();
+    req2.abort();
+
+    assert.equal(Object.keys(agent.sockets).length, 1);
+    assert.equal(Object.keys(agent.requests).length, 1);
+
+    console.log('Got res: ' + res1.statusCode);
+    console.dir(res1.headers);
+
+    res1.on('data', function(chunk) {
+      console.log('Read ' + chunk.length + ' bytes');
+      console.log(' chunk=%j', chunk.toString());
+      complete();
+    });
+
+    res1.on('end', function() {
+      console.log('Response ended.');
+
+      setTimeout(function() {
+        assert.equal(Object.keys(agent.sockets).length, 0);
+        assert.equal(Object.keys(agent.requests).length, 0);
+
+        server.close();
+      }, 100);
+    });
+  });
+
+  req1.end();
+});