From c6679d43fbc63840755e9e2e5c0e3a3063537284 Mon Sep 17 00:00:00 2001
From: Chris Tate <chris@ctate.dev>
Date: Sun, 25 Oct 2026 08:18:46 -0500
Subject: [PATCH] Add no empty chunk to a byte-mode Readable's buffer

push() of an empty Buffer outside object mode put a zero-length entry
into the read buffer, and the chunks pushed after it stalled behind it:
a 'data' listener saw nothing more and a readline interface never
closed. Node's readableAddChunk adds no empty chunk outside object mode;
it clears the reading flag and may read more. The runtime now does the
same, as it already did for an encoded push that decodes to nothing.
---
 .../corpus/7516-readable-empty-push.ts.json   |  6 ++
 packages/runtime/src/scr_stream.c             |  8 ++-
 tests/corpus/7516-readable-empty-push.ts      | 69 +++++++++++++++++++
 .../7516-readable-empty-push.ts.json          |  1 +
 4 files changed, 83 insertions(+), 1 deletion(-)
 create mode 100644 packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7516-readable-empty-push.ts.json
 create mode 100644 tests/corpus/7516-readable-empty-push.ts
 create mode 100644 tests/harness/corpus-costs/7516-readable-empty-push.ts.json

diff --git a/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7516-readable-empty-push.ts.json b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7516-readable-empty-push.ts.json
new file mode 100644
index 000000000..9388c4f9a
--- /dev/null
+++ b/packages/compiler/test/ts7/baselines/order-parity/tests/corpus/7516-readable-empty-push.ts.json
@@ -0,0 +1,6 @@
+{
+ "order": [
+  "<repo>/tests/corpus/7516-readable-empty-push.ts"
+ ],
+ "diags": []
+}
diff --git a/packages/runtime/src/scr_stream.c b/packages/runtime/src/scr_stream.c
index 406d91599..201d6e34b 100644
--- a/packages/runtime/src/scr_stream.c
+++ b/packages/runtime/src/scr_stream.c
@@ -954,8 +954,14 @@ static bool scr_stream_add_chunk(ScrStream *s, ScrBytes *chunk, bool front) {
     }
     entry = dec; /* owned */
   } else {
-    entry = scr_bytes_retain(chunk);
     entry_len = chunk->len;
+    if (entry_len == 0) {
+      /* Node's readableAddChunk adds no empty chunk outside object mode:
+       * it clears reading and may read more */
+      if (!front) scr_stream_maybe_read_more(s);
+      return !st->r.ended && (st->r.length < st->r.hwm || st->r.length == 0);
+    }
+    entry = scr_bytes_retain(chunk);
   }
   if (entry_len > 0 &&
       st->r.flowing == 1 && st->r.length == 0 && !st->r.in_read_sync && !front &&
diff --git a/tests/corpus/7516-readable-empty-push.ts b/tests/corpus/7516-readable-empty-push.ts
new file mode 100644
index 000000000..27d88e3ed
--- /dev/null
+++ b/tests/corpus/7516-readable-empty-push.ts
@@ -0,0 +1,69 @@
+// readable.push() of an empty Buffer outside object mode adds nothing, as
+// in Node: the chunks pushed after it still reach 'data' listeners,
+// readline and read(), and push(null) still ends the stream. In object
+// mode an empty Buffer is a value like any other.
+import { createInterface } from "node:readline";
+import { Readable } from "node:stream";
+
+function lines(chunks: string[]): Promise<void> {
+  return new Promise<void>((resolve) => {
+    const src = new Readable({ read() {} });
+    const rl = createInterface({ input: src, crlfDelay: Infinity });
+    rl.on("line", (line: string) => console.log("line", JSON.stringify(line)));
+    rl.on("close", () => {
+      console.log("readline closed");
+      resolve();
+    });
+    for (const chunk of chunks) src.push(Buffer.from(chunk, "utf8"));
+    src.push(null);
+  });
+}
+
+function data(): Promise<void> {
+  return new Promise<void>((resolve) => {
+    const src = new Readable({ read() {} });
+    src.on("data", (chunk: Buffer) => console.log("data", JSON.stringify(String(chunk))));
+    src.on("end", () => {
+      console.log("data end");
+      resolve();
+    });
+    console.log("push a", src.push(Buffer.from("a")));
+    console.log("push empty", src.push(Buffer.alloc(0)));
+    console.log("push b", src.push(Buffer.from("b")));
+    src.push(null);
+  });
+}
+
+function paused(): void {
+  const src = new Readable({ read() {} });
+  src.push(Buffer.from("x"));
+  src.push(Buffer.alloc(0));
+  src.push(Buffer.from("y"));
+  console.log("readableLength", src.readableLength);
+  console.log("read", JSON.stringify(String(src.read())));
+}
+
+function objectMode(): Promise<void> {
+  return new Promise<void>((resolve) => {
+    const src = new Readable({ objectMode: true, read() {} });
+    src.on("data", (chunk: Buffer) => console.log("object chunk length", chunk.length));
+    src.on("end", () => {
+      console.log("object end");
+      resolve();
+    });
+    src.push(Buffer.alloc(0));
+    src.push(Buffer.from("z"));
+    src.push(null);
+  });
+}
+
+async function main(): Promise<void> {
+  await lines(["a\nb", "", "c\n"]);
+  await lines(["", "", "only\n"]);
+  await data();
+  paused();
+  await objectMode();
+  console.log("done");
+}
+
+main();
diff --git a/tests/harness/corpus-costs/7516-readable-empty-push.ts.json b/tests/harness/corpus-costs/7516-readable-empty-push.ts.json
new file mode 100644
index 000000000..1cfe56769
--- /dev/null
+++ b/tests/harness/corpus-costs/7516-readable-empty-push.ts.json
@@ -0,0 +1 @@
+{ "plain": 2200, "san": 3200 }