From 14fa2b1abef4ada9fc3c32f07c7596b0a3aa898b Mon Sep 17 00:00:00 2001
From: aleister1102 <marucube35@gmail.com>
Date: Thu, 11 Jun 2026 14:15:40 +0700
Subject: [PATCH 1/2] fix(batch): add missing early return in
 nodeHttpBatchRpcResponse on non-POST
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Content-Transfer-Encoding: 8bit

Without response.end() and return, a non-POST request would write the
405 status line then fall through into the full RPC pipeline. This caused
the subsequent writeHead(200) to throw ERR_HTTP_HEADERS_SENT, left the
TCP connection open (response.end never called), and — when the caller
uses the documented try/catch pattern — caused a second writeHead(500)
to throw uncaught, terminating the Node.js process.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
---
 src/batch.ts | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/batch.ts b/src/batch.ts
index 4f423c7..85d1a10 100644
--- a/src/batch.ts
+++ b/src/batch.ts
@@ -179,6 +179,8 @@ export async function nodeHttpBatchRpcResponse(
     }): Promise<void> {
   if (request.method !== "POST") {
     response.writeHead(405, "This endpoint only accepts POST requests.");
+    response.end();
+    return;
   }
 
   let body = await new Promise<string>((resolve, reject) => {

From f684df8c85401038020c3e2980790bd158ced555 Mon Sep 17 00:00:00 2001
From: aleister1102 <marucube35@gmail.com>
Date: Thu, 11 Jun 2026 23:36:53 +0700
Subject: [PATCH 2/2] test(batch): add 405 regression test for non-POST
 requests

Add changeset for nodeHttpBatchRpcResponse early-return fix.
---
 .changeset/non-post-early-return.md | 6 ++++++
 __tests__/index.test.ts             | 6 ++++++
 2 files changed, 12 insertions(+)
 create mode 100644 .changeset/non-post-early-return.md

diff --git a/.changeset/non-post-early-return.md b/.changeset/non-post-early-return.md
new file mode 100644
index 0000000..739b11c
--- /dev/null
+++ b/.changeset/non-post-early-return.md
@@ -0,0 +1,6 @@
+---
+"capnweb": patch
+---
+
+Fix nodeHttpBatchRpcResponse leaving the connection open and crashing with
+ERR_HTTP_HEADERS_SENT on non-POST requests. It now returns 405 immediately.
diff --git a/__tests__/index.test.ts b/__tests__/index.test.ts
index fdf41b3..7ab5145 100644
--- a/__tests__/index.test.ts
+++ b/__tests__/index.test.ts
@@ -1935,6 +1935,12 @@ describe("HTTP requests", () => {
     expect(await Promise.all([promise1, promise2, promise3]))
         .toStrictEqual([36, 5, 9]);
   });
+
+  it("rejects non-POST requests with 405", async () => {
+    let response = await fetch(`http://${inject("testServerHost")}`, { method: "GET" });
+    expect(response.status).toBe(405);
+    await response.text();
+  });
 });
 
 describe("WebSockets", () => {