From 7ad32f944f53d460f0ac305f7f68876139f9a3f8 Mon Sep 17 00:00:00 2001
From: Gregory Terzian <2792687+gterzian@users.noreply.github.com>
Date: Tue, 5 Aug 2025 05:42:25 +0800
Subject: [PATCH] script: allow for undefined chunks in stream piping (#38470)

Current code uses `undefined` as chunk value to identify the closing of
a stream, but this breaks once you start streaming a chunk that is
actually `undefined`, as shown in
https://github.com/servo/servo/pull/38466. This PR re-implement the
logic in a way that allows for chunks to be `undefined`.

Testing: Should maintain `streams/piping` WPT pass rates. Also makes the
`undefined` case of
[`/encoding/streams/encode-bad-chunks.any.js`](https://github.com/servo/servo/blob/c59ee57b5d1ad0d6c2c6db10e15e3c53d243d0f2/tests/wpt/tests/encoding/streams/encode-bad-chunks.any.js#L29),
but that is only noticeable in https://github.com/servo/servo/pull/38466
Fixes: None, but noted in https://github.com/servo/servo/pull/38466

Signed-off-by: gterzian <2792687+gterzian@users.noreply.github.com>
---
 components/script/dom/readablestream.rs | 30 ++++++-------------------
 1 file changed, 7 insertions(+), 23 deletions(-)

diff --git a/components/script/dom/readablestream.rs b/components/script/dom/readablestream.rs
index adc45449d1e..b8dda723c7f 100644
--- a/components/script/dom/readablestream.rs
+++ b/components/script/dom/readablestream.rs
@@ -249,28 +249,7 @@ impl Callback for PipeTo {
                 // If dest.[[state]] is "writable",
                 // and ! WritableStreamCloseQueuedOrInFlight(dest) is false,
                 if dest.is_writable() && !dest.close_queued_or_in_flight() {
-                    let has_done = {
-                        if !result.is_object() {
-                            false
-                        } else {
-                            rooted!(in(*cx) let object = result.to_object());
-                            rooted!(in(*cx) let mut done = UndefinedValue());
-                            unsafe {
-                                get_dictionary_property(
-                                    *cx,
-                                    object.handle(),
-                                    "done",
-                                    done.handle_mut(),
-                                    can_gc,
-                                )
-                                .unwrap()
-                            }
-                        }
-                    };
-                    // If any chunks have been read but not yet written, write them to dest.
-                    let contained_bytes = self.write_chunk(cx, &global, result, can_gc);
-
-                    if !contained_bytes && !has_done {
+                    let Ok(done) = get_read_promise_done(cx, &result, can_gc) else {
                         // This is the case that the microtask ran in reaction
                         // to the closed promise of the reader,
                         // so we should wait for subsequent chunks,
@@ -278,6 +257,11 @@ impl Callback for PipeTo {
                         // (reader is closed, but there are still pending reads).
                         // Shutdown will happen when the last chunk has been received.
                         return;
+                    };
+
+                    if !done {
+                        // If any chunks have been read but not yet written, write them to dest.
+                        self.write_chunk(cx, &global, result, can_gc);
                     }
                 }
             }
@@ -446,7 +430,7 @@ impl PipeTo {
                 get_dictionary_property(*cx, object.handle(), "value", bytes.handle_mut(), can_gc)
                     .expect("Chunk should have a value.")
             };
-            if !bytes.is_undefined() && has_value {
+            if has_value {
                 // Write the chunk.
                 let write_promise = self.writer.write(cx, global, bytes.handle(), can_gc);
                 self.pending_writes.borrow_mut().push_back(write_promise);