stream: emit .write() end error in next tick.

This changes the behaviour of error event emitted when writing to a stream
after it has ended, from synchronously to asynchronously.

PR-URL: #4749

Author: phillipj

lib/_stream_writable.js

@@ -155,11 +155,10 @@ Writable.prototype.pipe = function() {
 };
 
 
-function writeAfterEnd(stream, cb) {
-  var er = new Error('write after end');
-  // TODO: defer error events consistently everywhere, not just the cb
-  stream.emit('error', er);
-  process.nextTick(cb, er);
+function writeAfterEndErr(stream, cb) {
+  const err = new Error('write after end');
+  stream.emit('error', err);
+  cb(err);
 }
 
 // If we get something that is not a buffer, string, null, or undefined,
@@ -201,7 +200,7 @@ Writable.prototype.write = function(chunk, encoding, cb) {
     cb = nop;
 
   if (state.ended)
-    writeAfterEnd(this, cb);
+    process.nextTick(writeAfterEndErr, this, cb);
   else if (validChunk(this, state, chunk, cb)) {
     state.pendingcb++;
     ret = writeOrBuffer(this, state, chunk, encoding, cb);

test/parallel/test-file-write-stream.js

@@ -15,7 +15,8 @@ var EXPECTED = '012345678910';
 var callbacks = {
   open: -1,
   drain: -2,
-  close: -1
+  close: -1,
+  error: -1
 };
 
 file
@@ -25,6 +26,10 @@ file
     assert.equal('number', typeof fd);
   })
   .on('error', function(err) {
+    // we're expecting write after end error
+    if (err.message === 'write after end') {
+      return callbacks.error++;
+    }
     throw err;
   })
   .on('drain', function() {
@@ -43,10 +48,9 @@ file
     assert.strictEqual(file.bytesWritten, EXPECTED.length * 2);
 
     callbacks.close++;
-    assert.throws(function() {
-      console.error('write after end should not be allowed');
-      file.write('should not work anymore');
-    });
+
+    console.error('write after end should not be allowed');
+    file.write('should not work anymore');
 
     fs.unlinkSync(fn);
   });

test/parallel/test-stream-writeable-write-ended-err.js

@@ -0,0 +1,31 @@
+'use strict';
+
+require('../common');
+
+const assert = require('assert');
+const Writable = require('stream').Writable;
+
+const stream = new Writable({ write });
+
+let errorsRecorded = 0;
+
+function write() {
+  throw new Error('write() should not have been called!');
+}
+
+function errorRecorder(err) {
+  if (err.message === 'write after end') {
+    errorsRecorded++;
+  }
+}
+
+// should trigger ended errors when writing later
+stream.end();
+
+stream.on('error', errorRecorder);
+stream.write('this should explode', errorRecorder);
+
+assert.equal(errorsRecorded, 0,
+  'Waits until next tick before emitting error');
+
+process.nextTick(() => assert.equal(errorsRecorded, 2));