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michealrobertsmichealroberts
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fix(miniflare): preserve request body length in dispatchFetch (#15906)
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4 files changed

Lines changed: 66 additions & 10 deletions

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‎.changeset/tidy-bodies-count.md‎

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@@ -0,0 +1,7 @@
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---
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"miniflare": patch
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---
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Preserve the request body length in `Miniflare#dispatchFetch()`
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Previously, a request with a known-length body (e.g. a string) was sent to the Worker chunked, without a `Content-Length`. Passing its `request.body` to `R2Bucket#put()` then failed with "Provided readable stream must have a known length", even though the same request works in production. The body's length is now preserved.

‎packages/miniflare/src/http/fetch.ts‎

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@@ -30,6 +30,10 @@ export async function fetch(
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`Fetch API cannot load: ${url.toString()}\nMake sure you're using http(s):// URLs for WebSocket requests via fetch.`
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);
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}
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// `ws` doesn't use `dispatcher`, so apply its origin rewrite here
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if (requestInit?.dispatcher instanceof DispatchFetchDispatcher) {
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requestInit.dispatcher.rewriteOrigin(url);
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}
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url.protocol = url.protocol.replace("http", "ws");
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// Normalise request headers to a format ws understands, extracting the
@@ -212,6 +216,14 @@ export class DispatchFetchDispatcher extends undici.Dispatcher {
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}
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}
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rewriteOrigin(/* mut */ url: URL) {
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if (url.origin === this.userRuntimeOrigin) {
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const runtimeURL = new URL(this.actualRuntimeOrigin);
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url.protocol = runtimeURL.protocol;
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url.host = runtimeURL.host;
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}
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}
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dispatch(
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/* mut */ options: undici.Dispatcher.DispatchOptions,
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handler: undici.Dispatcher.DispatchHandler

‎packages/miniflare/src/index.ts‎

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@@ -143,7 +143,7 @@ import type {
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ParsedInstanceOptions,
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ParsedWorkerOptions,
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} from "./config/schema";
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import type { DispatchFetch, RequestInit } from "./http";
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import type { DispatchFetch } from "./http";
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import type {
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DurableObjectClassNames,
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MiniflareFetcherBinding,
@@ -3124,13 +3124,8 @@ export class Miniflare {
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assert(this.#runtimeDispatcher !== undefined);
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const forward = new Request(input, init);
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const url = new URL(forward.url);
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const actualRuntimeOrigin = this.#runtimeEntryURL.origin;
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const userRuntimeOrigin = url.origin;
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// Rewrite URL for WebSocket requests which won't use `DispatchFetchDispatcher`
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url.protocol = this.#runtimeEntryURL.protocol;
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url.host = this.#runtimeEntryURL.host;
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const userRuntimeOrigin = new URL(forward.url).origin;
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// Remove `Content-Length: 0` headers from requests when a body is set to
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// avoid `RequestContentLengthMismatch` errors
@@ -3150,9 +3145,10 @@ export class Miniflare {
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cfBlob
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);
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const forwardInit = forward as RequestInit;
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forwardInit.dispatcher = dispatcher;
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const response = await fetch(url, forwardInit);
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// Pass `forward` as the input, not `init`, so its body keeps a known length.
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// As `init`, only the body stream is copied and it's sent chunked, which
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// APIs like `R2Bucket#put()` reject. `dispatcher` routes it to the runtime.
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const response = await fetch(forward, { dispatcher });
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// If the Worker threw an uncaught exception, propagate it to the caller
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const stack = response.headers.get(CoreHeaders.ERROR_STACK);

‎packages/miniflare/test/index.spec.ts‎

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@@ -22,6 +22,7 @@ import {
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LogLevel,
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Miniflare,
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MiniflareCoreError,
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Request,
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Response,
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viewToBuffer,
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} from "miniflare";
@@ -5183,3 +5184,43 @@ test("Miniflare: dispatchFetch handles POST/PUT with non-2xx status", async ({
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expect(await res.json()).toEqual({ method: "PUT", status });
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}
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});
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test("Miniflare: dispatchFetch() preserves request body length", async ({
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expect,
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}) => {
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const mf = new Miniflare({
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workers: [
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{
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config: {
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name: "",
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compatibilityDate: "2025-05-01",
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manifest: singleModuleManifest(`export default {
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async fetch(request, env) {
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await env.BUCKET.put("key", request.body);
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const object = await env.BUCKET.get("key");
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return Response.json({
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contentLength: request.headers.get("Content-Length"),
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body: await object.text(),
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});
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}
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}`),
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env: { BUCKET: { type: "r2", name: "BUCKET" } },
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},
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},
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],
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});
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useDispose(mf);
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// `R2Bucket#put()` requires a known length, as it does for requests with a
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// `Content-Length` in production
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let res = await mf.dispatchFetch("http://localhost/", {
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method: "PUT",
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body: "value",
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});
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expect(await res.json()).toEqual({ contentLength: "5", body: "value" });
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res = await mf.dispatchFetch(
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new Request("http://localhost/", { method: "PUT", body: "request" })
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);
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expect(await res.json()).toEqual({ contentLength: "7", body: "request" });
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});

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