Incorrect working of maxUploadSize option

[Nes-si]

New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server.

Issue Description

There is incorrect working of maxUploadSize Parse Server option. I've set up the option to '10mb', but I can't upload a file of, for example, 9 189 079 bytes — I've got an error "request entity too large". The correct loading is possible only when I set up the option to '12mb'.

Steps to reproduce

Just try to load a file with size of ≈ 9.2 MB.

Actual Outcome

Expected Outcome

Environment

Server

• Parse Server version: 5.2.7
• Operating system: macOS 10.15.7
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): local

Database

• System (MongoDB or Postgres): MongoDB
• Database version: 6.0.1
• Local or remote host (MongoDB Atlas, mLab, AWS, Azure, Google Cloud, etc): local

Client

• SDK (iOS, Android, JavaScript, PHP, Unity, etc): JS
• SDK version: 3.4.4

Logs

[parse-github-assistant]

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[mman]

From my quick look around the code, it appears that maxUploadSize parse server option gets directly passed as is into express router post method's limit param documented here: https://expressjs.com/en/4x/api.html#express where it controls the maximum (HTTP) request body size.

When uploading a file of size X bytes, it is probably expected, that its HTTP POST upload request body size will be larger than X by H bytes specifying the accompanying HTTP request headers at minimum.

I am not sure it is possible to infer value of H universally so better fix for this would be to properly document that maxUploadSize does not match 1:1 the file size, but rather explain that it specifies the request body size and should be set to larger values by factor of say 5%.

[mtrezza]

Anyone wants to open a PR to add that to the Parse Server option docs?

[Nes-si]

@mman I'm afraid 5% is too optimistic. My request for 9 189 079 file totals 12 252 273 bytes (33%).