fix: cleanup socker error handler on response

lib/application.js

@@ -98,7 +98,7 @@ app.callback = function(){
   return function(req, res, next){
     var ctx = self.createContext(req, res);
     next = next || ctx.onerror;
-    ctx.socket.once('error', next);
+    ctx.onSocketError(next);
     co.call(ctx, gen)(next);
   }
 };

lib/context.js

@@ -488,4 +488,20 @@ module.exports = {
   attachment: function() {
     return this.response.attachment.apply(this.response, arguments);
   },
+
+  /**
+   * Invoke `fn` on socket errors and
+   * handle cleanup on response.
+   *
+   * @param {Function} fn
+   * @api private
+   */
+
+  onSocketError: function(fn){
+    var sock = this.socket;
+    sock.once('error', fn);
+    this.res.on('finish', function(){
+      sock.removeListener('error', fn);
+    });
+  }
 };