http: always call response.write() callback

Ensure that the callback of `OutgoingMessage.prototype.write()` is
called even when writing empty chunks.

Fixes: https://github.com/nodejs/node/issues/22066

PR-URL: https://github.com/nodejs/node/pull/27709
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_outgoing.js

@@ -260,18 +260,6 @@ function _writeRaw(data, encoding, callback) {
     // There might be pending data in the this.output buffer.
     if (this.outputData.length) {
       this._flushOutput(conn);
-    } else if (!data.length) {
-      if (typeof callback === 'function') {
-        // If the socket was set directly it won't be correctly initialized
-        // with an async_id_symbol.
-        // TODO(AndreasMadsen): @trevnorris suggested some more correct
-        // solutions in:
-        // https://github.com/nodejs/node/pull/14389/files#r128522202
-        defaultTriggerAsyncIdScope(conn[async_id_symbol],
-                                   process.nextTick,
-                                   callback);
-      }
-      return true;
     }
     // Directly write to socket.
     return conn.write(data, encoding, callback);
@@ -593,14 +581,6 @@ function write_(msg, chunk, encoding, callback, fromEnd) {
                                    ['string', 'Buffer'], chunk);
   }
 
-
-  // If we get an empty string or buffer, then just do nothing, and
-  // signal the user to keep writing.
-  if (chunk.length === 0) {
-    debug('received empty string or buffer and waiting for more input');
-    return true;
-  }
-
   if (!fromEnd && msg.connection && !msg[kIsCorked]) {
     msg.connection.cork();
     msg[kIsCorked] = true;
@@ -608,7 +588,7 @@ function write_(msg, chunk, encoding, callback, fromEnd) {
   }
 
   var len, ret;
-  if (msg.chunkedEncoding) {
+  if (msg.chunkedEncoding && chunk.length !== 0) {
     if (typeof chunk === 'string')
       len = Buffer.byteLength(chunk, encoding);
     else

test/parallel/test-http-outgoing-message-inheritance.js

@@ -10,19 +10,23 @@ const assert = require('assert');
 // Fixes: https://github.com/nodejs/node/issues/14381
 
 class Response extends OutgoingMessage {
-  constructor() {
-    super({ method: 'GET', httpVersionMajor: 1, httpVersionMinor: 1 });
-  }
-
   _implicitHeader() {}
 }
 
 const res = new Response();
+
+let firstChunk = true;
+
 const ws = new Writable({
   write: common.mustCall((chunk, encoding, callback) => {
-    assert(chunk.toString().match(/hello world/));
+    if (firstChunk) {
+      assert(chunk.toString().endsWith('hello world'));
+      firstChunk = false;
+    } else {
+      assert.strictEqual(chunk.length, 0);
+    }
     setImmediate(callback);
-  })
+  }, 2)
 });
 
 res.socket = ws;

test/parallel/test-http-outgoing-message-write-callback.js

@@ -0,0 +1,37 @@
+'use strict';
+
+const common = require('../common');
+
+// This test ensures that the callback of `OutgoingMessage.prototype.write()` is
+// called also when writing empty chunks.
+
+const assert = require('assert');
+const http = require('http');
+const stream = require('stream');
+
+const expected = ['a', 'b', '', Buffer.alloc(0), 'c'];
+const results = [];
+
+const writable = new stream.Writable({
+  write(chunk, encoding, callback) {
+    setImmediate(callback);
+  }
+});
+
+const res = new http.ServerResponse({
+  method: 'GET',
+  httpVersionMajor: 1,
+  httpVersionMinor: 1
+});
+
+res.assignSocket(writable);
+
+for (const chunk of expected) {
+  res.write(chunk, () => {
+    results.push(chunk);
+  });
+}
+
+res.end(common.mustCall(() => {
+  assert.deepStrictEqual(results, expected);
+}));

test/parallel/test-http-server-response-standalone.js

@@ -15,11 +15,18 @@ const res = new ServerResponse({
   httpVersionMinor: 1
 });
 
+let firstChunk = true;
+
 const ws = new Writable({
   write: common.mustCall((chunk, encoding, callback) => {
-    assert(chunk.toString().match(/hello world/));
+    if (firstChunk) {
+      assert(chunk.toString().endsWith('hello world'));
+      firstChunk = false;
+    } else {
+      assert.strictEqual(chunk.length, 0);
+    }
     setImmediate(callback);
-  })
+  }, 2)
 });
 
 res.assignSocket(ws);