From ce4b1b2f33ac94ce9e923af8c1f6de0610230e1a Mon Sep 17 00:00:00 2001
From: Kristin Cowalcijk <kristincowalcijk@gmail.com>
Date: Sat, 11 Jul 2026 21:06:41 +0800
Subject: [PATCH] fix(fetch): propagate stream abort errors

---
 packages/fetch/src/stream.test.ts | 55 +++++++++++++++++++++++++++++++
 packages/fetch/src/stream.ts      |  5 ++-
 2 files changed, 59 insertions(+), 1 deletion(-)

diff --git a/packages/fetch/src/stream.test.ts b/packages/fetch/src/stream.test.ts
index 084002ac54a..937b464c649 100644
--- a/packages/fetch/src/stream.test.ts
+++ b/packages/fetch/src/stream.test.ts
@@ -21,6 +21,23 @@ function createMockResponse(sseLines: string[]): Response {
   } as unknown as Response;
 }
 
+function createMockResponseFromChunks(chunks: string[]): Response {
+  const stream = new Readable({
+    read() {
+      for (const chunk of chunks) {
+        this.push(chunk);
+      }
+      this.push(null);
+    },
+  }) as any;
+
+  return {
+    status: 200,
+    body: stream,
+    text: async () => "",
+  } as unknown as Response;
+}
+
 describe("streamSse", () => {
   it("yields parsed SSE data objects that ends with `data:[DONE]`", async () => {
     const sseLines = [
@@ -54,6 +71,44 @@ describe("streamSse", () => {
     expect(results).toEqual([{ foo: "bar" }, { baz: 42 }]);
   });
 
+  it("propogate AbortError when the stream is aborted with partial buffer", async () => {
+    // Simulate an abort mid-stream: the stream emits one complete SSE event,
+    // then a partial `data:` line (no trailing newline),
+    // then throws AbortError. The AbortError must propagate to the caller
+    // and not be swallowed, and the partial buffer must not be parsed.
+    async function* abortedStream() {
+      yield Buffer.from('data: {"foo": "bar"}\n\n');
+      yield Buffer.from('data: {"foo": "ba'); // partial - no newline
+      const abortError = new Error("The operation was aborted");
+      abortError.name = "AbortError";
+      throw abortError;
+    }
+
+    const stream = Readable.from(abortedStream()) as any;
+    const response = {
+      status: 200,
+      body: stream,
+      text: async () => "",
+    } as unknown as Response;
+
+    const results = [];
+    let caught: Error | undefined;
+    try {
+      for await (const data of streamSse(response)) {
+        results.push(data);
+      }
+    } catch (err) {
+      caught = err as Error;
+    }
+
+    // The first complete SSE event should be yielded before the abort occurs
+    expect(results).toEqual([{ foo: "bar" }]);
+
+    // The AbortError should be propagated to the caller, and not swallowed
+    expect(caught).toBeDefined();
+    expect(caught!.name).toBe("AbortError");
+  });
+
   it("throws on malformed JSON", async () => {
     const sseLines = ['data: {"foo": "bar"', "data:[DONE]"];
     const response = createMockResponse(sseLines);
diff --git a/packages/fetch/src/stream.ts b/packages/fetch/src/stream.ts
index f73d61dbafc..a6195f8cd28 100644
--- a/packages/fetch/src/stream.ts
+++ b/packages/fetch/src/stream.ts
@@ -49,7 +49,10 @@ export async function* streamResponse(
   } catch (e) {
     if (e instanceof Error) {
       if (e.name.startsWith("AbortError")) {
-        return; // In case of client-side cancellation, just return
+        // Let callers know that the request was aborted, so they can handle it accordingly,
+        // especially not try parsing the left over buffers, which might be incomplete and
+        // cause a JSON parsing error.
+        throw e;
       }
       if (e.message.toLowerCase().includes("premature close")) {
         // Premature close can happen for various reasons, including: