http: call write callback even if there is no message body

Ensure that the callback of `OutgoingMessage.prototype.write()` is
called when `outgoingMessage._hasBody` is `false` (HEAD method, 204
status code, etc.).
Refs: #27709
PR-URL: #27777
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>

Author: lpinca

lib/_http_outgoing.js

@@ -573,6 +573,7 @@ function write_(msg, chunk, encoding, callback, fromEnd) {
 if(!msg._hasBody){
 debug('This type of response MUST NOT have a body. '+
 'Ignoring write() calls.');
+if(callback)process.nextTick(callback);
 returntrue;
 }
 

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

@@ -3,35 +3,37 @@
 constcommon=require('../common');
 
 // This test ensures that the callback of `OutgoingMessage.prototype.write()` is
-// called also when writing empty chunks.
+// called also when writing empty chunks or when the message has no body.
 
 constassert=require('assert');
 consthttp=require('http');
 conststream=require('stream');
 
-constexpected=['a','b','',Buffer.alloc(0),'c'];
-constresults=[];
+for(constmethodof['GET, HEAD']){
+constexpected=['a','b','',Buffer.alloc(0),'c'];
+constresults=[];
 
-constwritable=newstream.Writable({
-write(chunk,encoding,callback){
-setImmediate(callback);
-}
-});
+constwritable=newstream.Writable({
+write(chunk,encoding,callback){
+callback();
+}
+});
 
-constres=newhttp.ServerResponse({
-method: 'GET',
-httpVersionMajor: 1,
-httpVersionMinor: 1
-});
+constres=newhttp.ServerResponse({
+method: method,
+httpVersionMajor: 1,
+httpVersionMinor: 1
+});
 
-res.assignSocket(writable);
+res.assignSocket(writable);
 
-for(constchunkofexpected){
-res.write(chunk,()=>{
-results.push(chunk);
-});
-}
+for(constchunkofexpected){
+res.write(chunk,()=>{
+results.push(chunk);
+});
+}
 
-res.end(common.mustCall(()=>{
-assert.deepStrictEqual(results,expected);
-}));
+res.end(common.mustCall(()=>{
+assert.deepStrictEqual(results,expected);
+}));
+}