TypeError: Can't read from request stream after response has been sent. when use stub.fetch(request)

[anusoft]

I want to read JSON body sent by HTTP POST (application/json) from Durable Object class, however I cannot read request.headers, request.text(), request.json() inside Durable object class, fetch function.

Refer from Durable Object Runtime APIs Document:

https://developers.cloudflare.com/workers/runtime-apis/durable-objects/#sending-http-requests

let response = await stub.fetch(request);
let response = await stub.fetch(url, options);

and if you modify Counter example from

let resp = await obj.fetch(request.url);

to

let resp = await obj.fetch(request);

And send request to wrangler dev (wrangler 1.19.12) you'll got error

TypeError: Can't read from request stream after response has been sent. at line 0, col -2
{
  "exceptionDetails": {
    "columnNumber": -2,
    "exception": {
      "className": "TypeError",
      "description": "TypeError: Can't read from request stream after response has been sent.",
      "preview": {
        "description": "TypeError: Can't read from request stream after response has been sent.",
        "entries": null,
        "overflow": false,
        "properties": [
          {
            "name": "stack",
            "subtype": null,
            "type": "string",
            "value": "TypeError: Can't read from request stream after response has been sent.",
            "valuePreview": null
          },
          {
            "name": "message",
            "subtype": null,
            "type": "string",
            "value": "Can't read from request stream after response has been sent.",
            "valuePreview": null
          }
        ],
        "subtype": "error",
        "type": "object"
      },
      "subtype": "error",
      "type": "object",
      "value": null
    },
    "lineNumber": 0,
    "text": "Uncaught (async)",
    "url": "undefined"
  },
  "timestamp": 1655635954748
}

[a-robinson]

Hm, I'm able to make the change you describe and then use wrangler dev without any issues. To be specific, I appleid this diff and then ran npx wrangler dev, then sent some requests to the various paths:

diff --git a/src/index.mjs b/src/index.mjs
index 4d35dab..3886ae4 100644
--- a/src/index.mjs
+++ b/src/index.mjs
@@ -9,7 +9,7 @@ export default {
 async function handleRequest(request, env) {
   let id = env.COUNTER.idFromName("A");
   let obj = env.COUNTER.get(id);
-  let resp = await obj.fetch(request.url);
+  let resp = await obj.fetch(request);
   let count = await resp.text();

   return new Response("Durable Object 'A' count: " + count);

I am using a newer wrangler version (2.0.6), but I wouldn't expect that to change any behavior within the worker. Does that diff match the extent of your changes or have you modified it in any other ways? I'm not seeing how the existing code on master plus your change could possibly be accessing the request after sending a response.

[anusoft]

I forgot to mention that I've tested with POST method, it's working when deploy/publish to cloudflare but not in wranger dev

index.mjs

// Worker

export default {
  async fetch(request, env) {
    return await handleRequest(request, env);
  }
}

async function handleRequest(request, env) {
  let id = env.COUNTER.idFromName("A");
  let obj = env.COUNTER.get(id);
  let resp = await obj.fetch(request.url);
  let count = await resp.text();

  return new Response("Durable Object 'A' count: " + count);
}

// Durable Object

export class Counter {
  constructor(state, env) {
    this.state = state;
  }

  // Handle HTTP requests from clients.
  async fetch(request) {
    // Apply requested action.
    let url = new URL(request.url);

    // Durable Object storage is automatically cached in-memory, so reading the
    // same key every request is fast. (That said, you could also store the
    // value in a class member if you prefer.)
    let value = await this.state.storage.get("value") || 0;

    switch (url.pathname) {
    case "/increment":
      ++value;
      break;
    case "/decrement":
      --value;
      break;
    case "/":
      // Just serve the current value.
      break;
    default:
      return new Response("Not found", {status: 404});
    }

    // We don't have to worry about a concurrent request having modified the
    // value in storage because "input gates" will automatically protect against
    // unwanted concurrency. So, read-modify-write is safe. For more details,
    // see: https://blog.cloudflare.com/durable-objects-easy-fast-correct-choose-three/
    await this.state.storage.put("value", value);

    return new Response(value);
  }
}

Test Command

curl --location --request POST 'http://127.0.0.1:8787/test' \
--header 'Content-Type: application/json' \
--data-raw '{ }'

Full Error Message

TypeError: Can't read from request stream after response has been sent. at line 0, col -2
{
  "exceptionDetails": {
    "columnNumber": -2,
    "exception": {
      "className": "TypeError",
      "description": "TypeError: Can't read from request stream after response has been sent.",
      "preview": {
        "description": "TypeError: Can't read from request stream after response has been sent.",
        "entries": null,
        "overflow": false,
        "properties": [
          {
            "name": "stack",
            "subtype": null,
            "type": "string",
            "value": "TypeError: Can't read from request stream after response has been sent.",
            "valuePreview": null
          },
          {
            "name": "message",
            "subtype": null,
            "type": "string",
            "value": "Can't read from request stream after response has been sent.",
            "valuePreview": null
          }
        ],
        "subtype": "error",
        "type": "object"
      },
      "subtype": "error",
      "type": "object",
      "value": null
    },
    "lineNumber": 0,
    "text": "Uncaught (async)",
    "url": "undefined"
  },
  "timestamp": 1656000206058
}

[anusoft]

When tried to clone request object

  var requestCopy = request.clone()
  let resp = await obj.fetch(requestCopy);

I've received this warning

Your worker called response.clone(), but did not read the body of both clones. This is wasteful, as it forces the system to buffer the entire response body in memory, rather than streaming it through. This may cause your worker to be unexpectedly terminated for going over the memory limit. If you only meant to copy the response headers and metadata (e.g. in order to be able to modify them), use `new Response(response.body, response)` instead.

[anusoft]

My workaround is to read json post body from handleRequest and create new Request Object then send to durableObject.fetch instead, this way it will works in both in wrangler dev and on cloudflare

              let eventBody = JSON.stringify( {abc: 123} );
              let eventRequest = new Request( StatisticName, { body: eventBody, method: 'POST' } );
              let id = env.COUNTER.idFromName('test');
              let obj = env.COUNTER.get(id);
              let resp = await obj.fetch(eventRequest);

[a-robinson]

Thanks for the extra info! I am now seeing the error in wrangler dev's output, but note that I'm still seeing the requests succeed in the sense that they return the correct response. This is more of a warning than an actual error.

Also, the warning goes away if your durable object actually reads the body passed to it. For example, if I apply this diff to make the DO consume the body passed to it and then send a POST with a body, I get no errors:

diff --git a/src/index.mjs b/src/index.mjs
index 4d35dab..5a46ffb 100644
--- a/src/index.mjs
+++ b/src/index.mjs
@@ -9,7 +9,7 @@ export default {
 async function handleRequest(request, env) {
   let id = env.COUNTER.idFromName("A");
   let obj = env.COUNTER.get(id);
-  let resp = await obj.fetch(request.url);
+  let resp = await obj.fetch(request);
   let count = await resp.text();

   return new Response("Durable Object 'A' count: " + count);
@@ -26,6 +26,7 @@ export class Counter {
   async fetch(request) {
     // Apply requested action.
     let url = new URL(request.url);
+    let unused = await request.arrayBuffer();

     // Durable Object storage is automatically cached in-memory, so reading the
     // same key every request is fast. (That said, you could also store the

I'll open up a ticket internally to make note of this extra log line, but unless I'm missing something it isn't something that you should actively worry about. The two takeaways:

1. This is a warning more so than an error. Your worker and DO are still working properly and returning correct responses.
2. The warning goes away if the DO actually reads the body send to it.