bug: serverActions.bodySizeLimit is ignored

[TryingToImprove]

Link to the code that reproduces this issue

https://github.com/TryingToImprove/next-app-router-body-size-issue

To Reproduce

1. Start the application
2. Click submit button
3. It should not throw a error because the data posted is not the same size as what is expected

Current vs. Expected behavior

Should not fail - bodySizeLimit should work

Verify canary release

• I verified that the issue exists in the latest Next.js canary release

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 10 Pro
Binaries:
  Node: 18.17.0
  npm: N/A
  Yarn: N/A
  pnpm: 8.11.0
Relevant Packages:
  next: 14.0.4-canary.40
  eslint-config-next: N/A
  react: 18.2.0
  react-dom: 18.2.0
  typescript: 5.1.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

App Router

Additional context

Relevant code is here: TryingToImprove/next-app-router-body-size-issue@6efd384

[LavransBjerkestrand]

I'm having the same problem, set it to 64mb but in reality it just stays at 1mb/1,048,576 bytes. Tried numerical values but same result

[TryingToImprove]

I have done some investigation I think I have figured out what the issue is.

When using a Server Action as a action on a form the request to the server is a multipart request whereas if making the request in a click handler it a normal request.

When making a multipart request next have a different way of handling the decoding of the data where it uses busboy without any configurations. If busboy is used without any configuration the default limit for a field is 1MB which is way it get truncated.

The place where busboy is used is here: https://github.com/vercel/next.js/blob/canary/packages/next/src/server/app-render/action-handler.ts#L467-L470

There is a test for larger Server Actions here: https://github.com/vercel/next.js/blob/canary/test/e2e/app-dir/actions/app-action-size-limit-invalid.test.ts#L79-L120 however it is not testing for form-submits.

I am able to get it work by applying this

--- a/packages/next/src/server/app-render/action-handler.ts
+++ b/packages/next/src/server/app-render/action-handler.ts
@@ -463,8 +463,11 @@ export async function handleAction({

         if (isMultipartAction) {
           if (isFetchAction) {
+            const readableLimit = serverActions?.bodySizeLimit ?? '1 MB'
+            const limit = require('next/dist/compiled/bytes').parse(readableLimit)
+
             const busboy = require('busboy')
-            const bb = busboy({ headers: req.headers })
+            const bb = busboy({ headers: req.headers, limits: { fieldSize: limit } })
             req.pipe(bb)

             bound = await decodeReplyFromBusboy(bb, serverModuleMap)

However there seems to be a mismatch for how next and busboy handle size limits. next sets the limit for the entire body whereas busboy is for each of the fields.

I am not sure how to proceed from here.

[mikeacre]

I am having this issue as well.. forms were working no problem with server actions now all of a sudden today I am having this issue.

Why do devs just randomly decide to implement this kind of behavior? None of the config changes are working and now my forms are limited to 1MB which is insane.

[nikmatswace]

I'm also having this problem. Forms being limited to 1 MB is a really rough situation to be in if you want to do any kind of image/file uploading.

I'm at Next 14.0.4, is there any kind of workaround?

[TryingToImprove]

I'm also having this problem. Forms being limited to 1 MB is a really rough situation to be in if you want to do any kind of image/file uploading.

I'm at Next 14.0.4, is there any kind of workaround?

I think you would be able to do it with a client-side fetch and a API route.

function submit(formData){
   fetch('/api/upload', { method: 'POST', body: formData })
}

<form action={submit}>...

For large JSON you could do it without FormData

[IVEN21]

I'm having the same issue, I persist to handle file form submission in server action rather in client.

[JaedonSpurlock01]

I am also having this issue as well. I am trying to upload JSON data to Amazon S3.

[sendmenas]

Have the same problem. I am sending base64 file string and the data that is received in server action is always limited to 1048576 characters.

[github-actions]

This closed issue has been automatically locked because it had no new activity for 2 weeks. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.