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.

1 files changed, 15 insertions, 6 deletions

diff --git a/lib/_http_client.js b/lib/_http_client.js
index 50f10d168..1dcf7f027 100644
--- a/lib/_http_client.js
+++ b/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);
+    }
   });
 };