fix(batch): add missing early return in nodeHttpBatchRpcResponse on non-POST

.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.

__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", () => {

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) => {