Limit and File Handling on addToBody Option

[maxkre96]

Prerequisites

• I have written a descriptive issue title
• I have searched existing issues to ensure the bug has not already been reported

Fastify version

4.15.0

Plugin version

7.6.0

Node.js version

16.13

Operating system

macOS

Operating system version (i.e. 20.04, 11.3, 10)

13.3.1

Description

When using @fastify/multipart empty files are returned when the file size limit is exceeded (default: 1mb).

If I send files larger than the limit to the API and access them body, I receive empty files when the file size exceeds the limit.
e.g:

File with 1.1mb
{ data: undefined, filename: 'DJI_0366.JPG', encoding: '7bit', mimetype: 'image/jpeg', limit: true }

If the file is smaller then the limit everything works correctly and the data field is defined.

File with 0.8mb:

{ data: <Buffer ff d8 ff e0 00 10 4a 46 49 46 00 01 01 00 00 01 00 01 00 00 ff e2 02 28 49 43 43 5f 50 52 4f 46 49 4c 45 00 01 01 00 00 02 18 00 00 00 00 04 30 00 00 ... 212574 more bytes>, filename: 'DJI_0365.JPG', encoding: '7bit', mimetype: 'image/jpeg', limit: false }

Reason

file.on('limit', () => {
    lastFile.limit = true
  })
file.on('end', () => {
    if (!lastFile.limit) {
      lastFile.data = Buffer.concat(fileData)
    } else {
      lastFile.data = undefined
    }
})

Steps to Reproduce

Register module with the addToBody Option

app.register(fastifyMultipart, { addToBody: true });

And access the files e.g. using nestjs
@Post() post(@Body() body: { files: Buffer[] }): void { return this.appService.createFiles(body.files); }

Expected Behavior

Either ban this option or return a 413 error message if the file exceeds the size limit.
This is a serious issue that can result in data loss

[mcollina]

Thanks for reporting! Would you like to send a Pull Request to address this issue? Remember to add unit tests.

[Uzlopak]

Our busboy implementation will give the feedback that the file is to big and cut off the file stream. Thats why your big file is smaller. What is missing is Handling the feedback and error with file too big.

[gurgunday]

addToBody is not documented in the README anymore and I believe is deprecated. If you use attachFieldsToBody: true instead, it does throw when the limit is exceeded

Other than that, I think removing these undocumented options is the best way forward