stream: Guarantee ordering of 'finish' event

In synchronous Writable streams (where the _write cb is called on the
current tick), the 'finish' event (and thus the end() callback) can in
some cases be called before all the write() callbacks are called.

Use a counter, and have stream.Transform rely on the 'prefinish' event
instead of the 'finish' event.

This has zero effect on most streams, but it corrects an edge case and
makes it perform more deterministically, which is a Good Thing.

1 files changed, 16 insertions, 0 deletions

diff --git a/test/simple/test-stream2-writable.js b/test/simple/test-stream2-writable.js
index e0f384cb2a..704100c0da 100644
--- a/test/simple/test-stream2-writable.js
+++ b/test/simple/test-stream2-writable.js
@@ -375,3 +375,19 @@ test('finish does not come before write cb', function(t) {
   w.write(Buffer(0));
   w.end();
 });
+
+test('finish does not come before sync _write cb', function(t) {
+  var w = new W();
+  var writeCb = false;
+  w._write = function(chunk, e, cb) {
+    cb();
+  };
+  w.on('finish', function() {
+    assert(writeCb);
+    t.end();
+  });
+  w.write(Buffer(0), function(er) {
+    writeCb = true;
+  });
+  w.end();
+});