Remove "content-length: 0" from some requests

packages/core/src/standards/http.ts

@@ -700,6 +700,12 @@ const kDefaultHeadersToRemove = [
   "user-agent",
 ];
 
+const methodsExpectingPayload = [
+  "PUT",
+  "POST",
+  "PATCH"
+];
+
 class MiniflareDispatcher extends Dispatcher {
   // dispatch, close & destroy are the only methods a Dispatcher must implement:
   // https://github.com/nodejs/undici/blob/09059fb491b4158a25981eb5598262b43a18c6ae/lib/dispatcher.js
@@ -767,6 +773,13 @@ export async function fetch(
   req.headers.delete("cf-connecting-ip");
   // Add "MF-Loop" header for loop detection
   req.headers.set(_kLoopHeader, String(ctx?.requestDepth ?? 1));
+  // Delete "content-length: 0" from bodyless requests. Some proxies add this,
+  // but undici considers it an error.
+  // See https://github.com/cloudflare/miniflare/issues/193
+
+  if (!methodsExpectingPayload.includes(req.method) && req.headers.get("content-length") === "0") {
+    req.headers.delete("content-length");
+  }
 
   // Mark default headers for removal that aren't explicitly included
   const removeHeaders: string[] = [];

packages/core/test/standards/http.spec.ts

@@ -960,6 +960,23 @@ test("fetch: removes Host and CF-Connecting-IP headers from Request", async (t)
     "x-real-ip": "127.0.0.1",
   });
 });
+test("fetch: removes Content-Length 0 from body-less requests", async (t) => {
+  // Should remove content-length: 0 from certain methods because undici sees it
+  // as an error: https://github.com/cloudflare/miniflare/issues/193
+  const upstream = (
+    await useServer(t, (req, res) => res.end(JSON.stringify(req.headers)))
+  ).http;
+  const res = await fetch(upstream, {
+    method: "DELETE",
+    headers: {
+      "Content-Length": "0"
+    },
+  });
+  const headers = await res.json();
+  t.like(headers, {
+    host: upstream.host,
+  });
+});
 test("fetch: removes default fetch headers from Request unless explicitly added", async (t) => {
   // Should remove accept, accept-language, sec-fetch-mode, and user-agent
   // headers unless explicitly added: https://github.com/cloudflare/miniflare/issues/139