http: add missing stream-like properties to OutgoingMessage

PR-URL: #29018
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/_http_outgoing.js

@@ -112,7 +112,7 @@ Object.setPrototypeOf(OutgoingMessage.prototype, Stream.prototype);
 Object.setPrototypeOf(OutgoingMessage, Stream);
 
 Object.defineProperty(OutgoingMessage.prototype, 'writableFinished', {
-  get: function() {
+  get() {
     return (
       this.finished &&
       this.outputSize === 0 &&
@@ -121,6 +121,24 @@ Object.defineProperty(OutgoingMessage.prototype, 'writableFinished', {
   }
 });
 
+Object.defineProperty(OutgoingMessage.prototype, 'writableObjectMode', {
+  get() {
+    return false;
+  }
+});
+
+Object.defineProperty(OutgoingMessage.prototype, 'writableLength', {
+  get() {
+    return this.outputSize + (this.socket ? this.socket.writableLength : 0);
+  }
+});
+
+Object.defineProperty(OutgoingMessage.prototype, 'writableHighWaterMark', {
+  get() {
+    return this.socket ? this.socket.writableHighWaterMark : HIGH_WATER_MARK;
+  }
+});
+
 Object.defineProperty(OutgoingMessage.prototype, '_headers', {
   get: internalUtil.deprecate(function() {
     return this.getHeaders();

test/parallel/test-http-outgoing-properties.js

@@ -0,0 +1,53 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+const http = require('http');
+const OutgoingMessage = http.OutgoingMessage;
+
+{
+  const msg = new OutgoingMessage();
+  assert.strictEqual(msg.writableObjectMode, false);
+}
+
+{
+  const msg = new OutgoingMessage();
+  assert(msg.writableHighWaterMark > 0);
+}
+
+{
+  const server = http.createServer(common.mustCall(function(req, res) {
+    const hwm = req.socket.writableHighWaterMark;
+    assert.strictEqual(res.writableHighWaterMark, hwm);
+
+    assert.strictEqual(res.writableLength, 0);
+    res.write('');
+    const len = res.writableLength;
+    res.write('asd');
+    assert.strictEqual(res.writableLength, len + 8);
+    res.end();
+    res.on('finish', common.mustCall(() => {
+      assert.strictEqual(res.writableLength, 0);
+      server.close();
+    }));
+  }));
+
+  server.listen(0);
+
+  server.on('listening', common.mustCall(function() {
+    const clientRequest = http.request({
+      port: server.address().port,
+      method: 'GET',
+      path: '/'
+    });
+    clientRequest.end();
+  }));
+}
+
+{
+  const msg = new OutgoingMessage();
+  msg._implicitHeader = function() {};
+  assert.strictEqual(msg.writableLength, 0);
+  msg.write('asd');
+  assert.strictEqual(msg.writableLength, 7);
+}