http: overridable clientError

Make default `clientError` behavior (close socket immediately)
overridable. With this APIs it is possible to write a custom error
handler, and to send, for example, a 400 HTTP response.

    http.createServer(...).on('clientError', function(err, socket) {
      socket.end('HTTP/1.1 400 Bad Request\r\n\r\n');
      socket.destroy();
    });

Fix: nodejs#4543

doc/api/http.markdown

@@ -421,6 +421,10 @@ not be emitted.
 `function (exception, socket) { }`
 
 If a client connection emits an `'error'` event, it will be forwarded here.
+Listener of this event is responsible for destroying socket, and, for example,
+can do it it gracefully by sending 400 HTTP response.
+
+Default behavior is destroy socket immediately.
 
 `socket` is the [`net.Socket`][] object that the error originated from.
 

lib/_http_server.js

@@ -237,10 +237,6 @@ function Server(requestListener) {
 
   this.addListener('connection', connectionListener);
 
-  this.addListener('clientError', function(err, conn) {
-    conn.destroy(err);
-  });
-
   this.timeout = 2 * 60 * 1000;
 
   this._pendingResponseData = 0;
@@ -353,7 +349,8 @@ function connectionListener(socket) {
 
   // TODO(isaacs): Move all these functions out of here
   function socketOnError(e) {
-    self.emit('clientError', e, this);
+    if (!self.emit('clientError', e, this))
+      this.destroy(e);
   }
 
   function socketOnData(d) {

lib/https.js

@@ -29,8 +29,9 @@ function Server(opts, requestListener) {
     this.addListener('request', requestListener);
   }
 
-  this.addListener('clientError', function(err, conn) {
-    conn.destroy();
+  this.addListener('tlsClientError', function(err, conn) {
+    if (!this.emit('clientError', err, conn))
+      conn.destroy();
   });
 
   this.timeout = 2 * 60 * 1000;

test/parallel/test-http-client-abort.js

@@ -21,12 +21,6 @@ var server = http.Server(function(req, res) {
       server.close();
     }
   });
-
-  // since there is already clientError, maybe that would be appropriate,
-  // since "error" is magical
-  req.on('clientError', function() {
-    console.log('Got clientError');
-  });
 });
 
 var responses = 0;

test/parallel/test-https-timeout-server.js

@@ -32,6 +32,7 @@ server.on('clientError', function(err, conn) {
   assert.equal(conn._secureEstablished, false);
   server.close();
   clientErrors++;
+  conn.destroy();
 });
 
 server.listen(common.PORT, function() {