http: disable OutgoingMessage pipe method

OutgoingMessage should be a write-only stream, and it shouldn't
be piped. This commit disables the `pipe` method by throwing
an exception (if this method is called).

PR-URL: #14358
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

lib/_http_outgoing.js

@@ -889,6 +889,10 @@ OutgoingMessage.prototype.flush = internalUtil.deprecate(function() {
   this.flushHeaders();
 }, 'OutgoingMessage.flush is deprecated. Use flushHeaders instead.', 'DEP0001');
 
+OutgoingMessage.prototype.pipe = function pipe() {
+  // OutgoingMessage should be write-only. Piping from it is disabled.
+  this.emit('error', new Error('Cannot pipe, not readable'));
+};
 
 module.exports = {
   OutgoingMessage

test/parallel/test-outgoing-message-pipe.js

@@ -0,0 +1,15 @@
+'use strict';
+const assert = require('assert');
+const common = require('../common');
+const OutgoingMessage = require('_http_outgoing').OutgoingMessage;
+
+// Verify that an error is thrown upon a call to `OutgoingMessage.pipe`.
+
+const outgoingMessage = new OutgoingMessage();
+assert.throws(
+  common.mustCall(() => { outgoingMessage.pipe(outgoingMessage); }),
+  (err) => {
+    return ((err instanceof Error) && /Cannot pipe, not readable/.test(err));
+  },
+  'OutgoingMessage.pipe should throw an error'
+);