src: enable writev for pipe handles on Unix

This commit enables writev for Unix Domain Sockets on supported
platforms thus enabling cork/uncork functionality for them and
improving IPC performance.

Fixes: https://github.com/nodejs/node/issues/5095
PR-URL: https://github.com/nodejs/node/pull/10677
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/pipe_wrap.cc

@@ -53,7 +53,11 @@ void PipeWrap::Initialize(Local<Object> target,
   env->SetProtoMethod(t, "ref", HandleWrap::Ref);
   env->SetProtoMethod(t, "hasRef", HandleWrap::HasRef);
 
+#ifdef _WIN32
   StreamWrap::AddMethods(env, t);
+#else
+  StreamWrap::AddMethods(env, t, StreamBase::kFlagHasWritev);
+#endif
 
   env->SetProtoMethod(t, "bind", Bind);
   env->SetProtoMethod(t, "listen", Listen);

test/parallel/test-pipe-writev.js

@@ -0,0 +1,46 @@
+'use strict';
+
+const common = require('../common');
+const assert = require('assert');
+const net = require('net');
+
+if (common.isWindows) {
+  common.skip('Unix-specific test');
+  return;
+}
+
+common.refreshTmpDir();
+
+const server = net.createServer((connection) => {
+  connection.on('error', (err) => {
+    throw err;
+  });
+
+  const writev = connection._writev.bind(connection);
+  connection._writev = common.mustCall(writev);
+
+  connection.cork();
+  connection.write('pi');
+  connection.write('ng');
+  connection.end();
+});
+
+server.on('error', (err) => {
+  throw err;
+});
+
+server.listen(common.PIPE, () => {
+  const client = net.connect(common.PIPE);
+
+  client.on('error', (err) => {
+    throw err;
+  });
+
+  client.on('data', common.mustCall((data) => {
+    assert.strictEqual(data.toString(), 'ping');
+  }));
+
+  client.on('end', () => {
+    server.close();
+  });
+});