[question] why ECONRESET / ECONREFUSED - how to consume response body with fetch

[blephy]

Hi,

I have a nodejs server running with a DB. They are communicating throught HTTP with undici client

Here is my undici global agent :

const dnsCache = new CacheableLookup();
const agent = new Agent({
      // @ts-expect-error -- this is safe https://github.com/nodejs/undici/tree/main/docs/examples#using-cacheablelookup-to-cache-dns-lookups-in-undici
      connect: {
        lookup: dnsCache.lookup.bind(dnsCache),
        keepAlive: true,
        timeout: 10_000,
        allowH2: true,
      },
      bodyTimeout: 60_000,
      headersTimeout: 60_000,
      allowH2: true,
      keepAliveTimeout: 10_000,
    });

Sometime, i run into this error :

"err":{"type":"SocketError","message":"other side closed","stack":"SocketError: other side closed\n    at Socket.onHttpSocketEnd (/home/node/app/node_modules/.pnpm/undici@7.3.0/node_modules/undici/lib/dispatcher/client-h1.js:902:22)\n    at Socket.emit (node:events:530:35)\n    at endReadableNT (node:internal/streams/readable:1698:12)\n    at process.processTicksAndRejections (node:internal/process/task_queues:90:21)","name":"SocketError","code":"UND_ERR_SOCKET","socket":{"localAddress":"127.0.0.1","localPort":37560,"remoteAddress":"127.0.0.1","remotePort":8080,"remoteFamily":"IPv4","bytesWritten":62192889,"bytesRead":3705674}

and subsequence call produce then this error 3 or 4 times :

"err":{"type":"Error","message":"read ECONNRESET","stack":"Error: read ECONNRESET\n    at TCP.onStreamRead (node:internal/stream_base_commons:216:20)\n    at TCP.callbackTrampoline (node:internal/async_hooks:130:17)","errno":-104,"code":"ECONNRESET","syscall":"read"}

and after again, always this error in loop :

"err":{"type":"Error","message":"connect ECONNREFUSED 127.0.0.1:8080","stack":"Error: connect ECONNREFUSED 127.0.0.1:8080\n    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1634:16)\n    at TCPConnectWrap.callbackTrampoline (node:internal/async_hooks:130:17)","errno":-111,"code":"ECONNREFUSED","syscall":"connect","address":"127.0.0.1","port":8080}

To fix it, i need to resart the pod containing the app and the DB.

Can somebody explain to me if my configuration is not OP ?

Is this an undici bug which not re-open a socket after the previous one was closed by the DB ?

This can be a DB error too, but it would be great if someone here can explain to me what happens, i'm not even sure what to think about those errors.

Not related question : is CacheableLookup does the same as the dns interceptor ? Should i use dns interceptor then ? If so, we probably update your documentation

[blephy]

I think i maybe found the problem.

nb :

• https://stackoverflow.com/questions/76931498/typeerror-terminated-cause-socketerror-other-side-closed-in-fetch-nodejs
• SocketError: other side closed #583 (comment)

I'm using the undici fetch implementation in conjunction with GraphQlClient from graphql-request as follow :

import { fetch } from 'undici';

new GraphQLClient(
      new URL(endpoint, base).toString(),
      {
        keepalive: true,
        fetch: fetch,
      },
    );

But if we look at the GraphQLClient code, if a response is not OK, it does not consume the request body :

const fetchResponse = await fetcher(config)

  if (!fetchResponse.ok) {
    return new ClientError(
      { status: fetchResponse.status, headers: fetchResponse.headers },
      {
        query: input.request._tag === `Single` ? input.request.document.expression : input.request.query,
        variables: input.request.variables,
      },
    )
  }

So i will wrappe undici fetch implementation to consume the body only if the response is not ok like this :

import { fetch } from 'undici';

function myFetchUndici(...) {
  const response: Response = await fetch(input, init);

  if (!response.ok && response.bodyUsed) {
    await response.body?.cancel();
  }

  return response;
}

new GraphQLClient(
      new URL(endpoint, base).toString(),
      {
        keepalive: true,
        fetch: myFetchUndici,
      },
    );

But question : how to properly consume the request's body in this case with fetch ? request.body.cancel ? response.body?.getReader().cancel() ? response.clone() ?

I juste need to have access to response.status and response.headers after that, not to read the body. What is the safer / faster way to do it ?

[metcoder95]

response.cancel should be a good way to go