http: don't double-fire the req error event

req.socket._hadError should be set before emitting the error event.

PR-URL: nodejs/node#14659
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

lib/_http_client.js

@@ -373,8 +373,8 @@ function socketCloseListener() {
     // This socket error fired before we started to
     // receive a response. The error needs to
     // fire on the request.
-    req.emit('error', createHangUpError());
     req.socket._hadError = true;
+    req.emit('error', createHangUpError());
   }
 
   // Too bad.  That output wasn't getting written.
@@ -397,10 +397,10 @@ function socketErrorListener(err) {
   debug('SOCKET ERROR:', err.message, err.stack);
 
   if (req) {
-    req.emit('error', err);
     // For Safety. Some additional errors might fire later on
     // and we need to make sure we don't double-fire the error event.
     req.socket._hadError = true;
+    req.emit('error', err);
   }
 
   // Handle any pending data
@@ -433,8 +433,8 @@ function socketOnEnd() {
   if (!req.res && !req.socket._hadError) {
     // If we don't have a response then we know that the socket
     // ended prematurely and we need to emit an error on the request.
-    req.emit('error', createHangUpError());
     req.socket._hadError = true;
+    req.emit('error', createHangUpError());
   }
   if (parser) {
     parser.finish();
@@ -455,8 +455,8 @@ function socketOnData(d) {
     debug('parse error', ret);
     freeParser(parser, req, socket);
     socket.destroy();
-    req.emit('error', ret);
     req.socket._hadError = true;
+    req.emit('error', ret);
   } else if (parser.incoming && parser.incoming.upgrade) {
     // Upgrade or CONNECT
     var bytesParsed = ret;

test/parallel/test-http-client-req-error-dont-double-fire.js

@@ -0,0 +1,16 @@
+'use strict';
+const assert = require('assert');
+const http = require('http');
+const common = require('../common');
+
+// not exists host
+const host = '*'.repeat(256);
+const req = http.get({ host });
+const err = new Error('mock unexpected code error');
+req.on('error', common.mustCall(() => {
+  throw err;
+}));
+
+process.on('uncaughtException', common.mustCall((e) => {
+  assert.strictEqual(e, err);
+}));