[v12.x backport] http: only set keep-alive when not exists

lib/_http_outgoing.js

@@ -98,6 +98,7 @@ function OutgoingMessage() {
   this._last = false;
   this.chunkedEncoding = false;
   this.shouldKeepAlive = true;
+  this._defaultKeepAlive = true;
   this.useChunkedEncodingByDefault = true;
   this.sendDate = false;
   this._removedConnection = false;
@@ -405,8 +406,8 @@ function _storeHeader(firstLine, headers) {
         (state.contLen || this.useChunkedEncodingByDefault || this.agent);
     if (shouldSendKeepAlive) {
       header += 'Connection: keep-alive\r\n';
-      if (this._keepAliveTimeout) {
-        const timeoutSeconds = MathFloor(this._keepAliveTimeout) / 1000;
+      if (this._keepAliveTimeout && this._defaultKeepAlive) {
+        const timeoutSeconds = MathFloor(this._keepAliveTimeout / 1000);
         header += `Keep-Alive: timeout=${timeoutSeconds}\r\n`;
       }
     } else {
@@ -502,6 +503,9 @@ function matchHeader(self, state, field, value) {
     case 'trailer':
       state[field] = true;
       break;
+    case 'keep-alive':
+      self._defaultKeepAlive = false;
+      break;
   }
 }
 

test/parallel/test-http-keep-alive-timeout-custom.js

@@ -0,0 +1,31 @@
+'use strict';
+
+const common = require('../common');
+const http = require('http');
+const assert = require('assert');
+
+const server = http.createServer(common.mustCall((req, res) => {
+  const body = 'hello world\n';
+
+  res.writeHead(200, {
+    'Content-Length': body.length,
+    'Keep-Alive': 'timeout=50'
+  });
+  res.write(body);
+  res.end();
+}));
+server.keepAliveTimeout = 12010;
+
+const agent = new http.Agent({ maxSockets: 1, keepAlive: true });
+
+server.listen(0, common.mustCall(function() {
+  http.get({
+    path: '/', port: this.address().port, agent: agent
+  }, common.mustCall((response) => {
+    response.resume();
+    assert.strictEqual(
+      response.headers['keep-alive'], 'timeout=50');
+    server.close();
+    agent.destroy();
+  }));
+}));

test/parallel/test-http-keep-alive-timeout.js

@@ -11,7 +11,7 @@ const server = http.createServer(common.mustCall((req, res) => {
   res.write(body);
   res.end();
 }));
-server.keepAliveTimeout = 12000;
+server.keepAliveTimeout = 12010;
 
 const agent = new http.Agent({ maxSockets: 1, keepAlive: true });