From 70dee35733e1cd60b52ac34ce17f34e4df815a8a Mon Sep 17 00:00:00 2001
From: Mattias Buelens <mattias@buelens.com>
Date: Fri, 4 Jun 2021 23:37:41 +0200
Subject: [PATCH] Respond before enqueue in ReadableByteStreamTee

---
 index.bs                                                   | 7 +++++--
 .../lib/abstract-ops/readable-streams.js                   | 6 ++++--
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/index.bs b/index.bs
index 53fe8e8ad..bee5a6504 100644
--- a/index.bs
+++ b/index.bs
@@ -2399,10 +2399,13 @@ create them does not matter.
      1. Let |otherCanceled| be |canceled2| if |forBranch2| is false, and |canceled1| otherwise.
      1. If |otherCanceled| is false,
       1. Let |clonedChunk| be ? [$CloneAsUint8Array$](|chunk|).
+      1. If |byobCanceled| is false, perform !
+         [$ReadableByteStreamControllerRespondWithNewView$](|byobBranch|.[=ReadableStream/[[controller]]=],
+         |chunk|).
       1. Perform ! [$ReadableByteStreamControllerEnqueue$](|otherBranch|.[=ReadableStream/[[controller]]=],
          |clonedChunk|).
-     1. If |byobCanceled| is false,
-      1. Perform ! [$ReadableByteStreamControllerRespondWithNewView$](|byobBranch|.[=ReadableStream/[[controller]]=],
+     1. Otherwise, if |byobCanceled| is false, perform !
+        [$ReadableByteStreamControllerRespondWithNewView$](|byobBranch|.[=ReadableStream/[[controller]]=],
         |chunk|).
 
     <p class="note">The microtask delay here is necessary because it takes at least a microtask to
diff --git a/reference-implementation/lib/abstract-ops/readable-streams.js b/reference-implementation/lib/abstract-ops/readable-streams.js
index b622aa552..f19e53c37 100644
--- a/reference-implementation/lib/abstract-ops/readable-streams.js
+++ b/reference-implementation/lib/abstract-ops/readable-streams.js
@@ -557,9 +557,11 @@ function ReadableByteStreamTee(stream) {
 
           if (otherCanceled === false) {
             const clonedChunk = CloneAsUint8Array(chunk);
+            if (byobCanceled === false) {
+              ReadableByteStreamControllerRespondWithNewView(byobBranch._controller, chunk);
+            }
             ReadableByteStreamControllerEnqueue(otherBranch._controller, clonedChunk);
-          }
-          if (byobCanceled === false) {
+          } else if (byobCanceled === false) {
             ReadableByteStreamControllerRespondWithNewView(byobBranch._controller, chunk);
           }
         });