Body already used issue with certain libraries

[danieljvdm]

What versions are running?

...
"@bogeychan/elysia-logger": "^0.1.7",
"elysia": "^1.2.10",
"better-auth": "^1.1.10",
...

What steps can reproduce the bug?

My server looks like this:

new Elysia()
  .use(logger())
  .use(cors())
  .all('/api/auth/*', betterAuthView)
  .listen(getEnv().PORT);

betterAuthView is this:

export const betterAuthView = async (context: Context) => {
  const BETTER_AUTH_ACCEPT_METHODS = ['POST', 'GET'];
  if (BETTER_AUTH_ACCEPT_METHODS.includes(context.request.method)) {
    console.log(context.request);
    try {
      return auth.handler(context.request);
    } catch (error) {
      console.error('Error in auth.handler:', error);
      return context.error(500, 'Error in authentication handler');
    }
  } else {
    context.error(405);
  }
};

When a request goes to an auth route, I get a ERR_BODY_ALREADY_USED error. If I comment out this logger, it works fine. I'm not exactly sure what's going on, but the stacktrace of the error is on this line (in the better-auth libary):
return await request.json();

So it seems like that library is trying to consume the request body but by that time this logger already has...

What is the expected behavior?

No response

What do you see instead?

No response

Additional information

No response

[bogeychan]

Thanks for reporting this finding.

Elysia has built-in support for parsing application/json, ..., which is why your body is already used. However, due to (required) access of ctx in hooks in this plugin:

elysia-logger/src/index.ts

Line 152 in a1c27e5

log.error(ctx);

Elysia cannot determine whether the body property is being accessed or not. As a result, it pre-parses the body (context.body). You will encounter the same issue with new Elysia({ aot: false }) if you remove the plugin.

---

Here's a workaround to skip parsing:

.all("/api/auth/*", betterAuthView, { parse: () => 1 })

Kinda blocked by elysiajs/elysia#1009

[danieljvdm]

Thanks for the response. I don't quite follow what you're saying - this seems to be more localized to this library than other things. I'm getting the same issue on my GraphQL server - body is already used unless I disable this logger (there isn't an obvious way to pass { parse: () => 1} to a gql yoga instance either.)

Sorry if i'm not understanding things correctly - but is there no way this library can use response.clone() to avoid accessing the same response object?

[danieljvdm]

For now I've just moved my graphql yoga server above the logger call:

  .use(graphqlServer)
  .use(logger())

[bogeychan]

We need to wait until the mentioned Elysia issue is resolved.

If other plugins cause similar issues, you can work around it by adding a global parse-hook and manually handling parsing on the cloned request:

import { Elysia, ParseError } from "elysia";

const plugin = new Elysia({ name: "plugin" })
  .derive((ctx) => ({ plugin: ctx.body }))
  .as("global");

new Elysia()
  .onParse(({ request, contentType }) => {
    const cloned = request.clone();

    switch (contentType) {
      case "application/json":
        return cloned.json();
      case "text/plain":
        return cloned.text();
    }

    throw new ParseError();
  })
  .use(plugin)
  .post("/", ({ request }) => request.bodyUsed)
  .listen(3000);