React Router's fetcher fails to upload some images on Safari

[jmho]

I'm using React Router as a...

framework

Reproduction

1. Open up the following StackBlitz in Safari and Chrome
2. Download the following zip containing png images here
3. Extract the untitled folder from the zip file.
4. Upload any of the two images to the stackblitz instance opened in chrome and click submit.
5. Upload the same image as in step 4 to the stackblitz instance opened in safari and click submit.

Additional note:

• These .png images were created using the MacOS Snipping tool.

System Info

Stack Blitz
  System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 18.20.3 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.2.3 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @react-router/dev: * => 7.1.5 
    @react-router/node: * => 7.1.5 
    @react-router/serve: * => 7.1.5 
    react-router: * => 7.1.5 
    vite: ^6.0.11 => 6.1.0 

Local
  System:
    OS: macOS 15.3
    CPU: (10) arm64 Apple M1 Pro
    Memory: 137.61 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.11.1 - ~/.nvm/versions/node/v20.11.1/bin/node
    npm: 10.2.4 - ~/.nvm/versions/node/v20.11.1/bin/npm
    pnpm: 9.12.3 - ~/.nvm/versions/node/v20.11.1/bin/pnpm
    bun: 1.1.0 - ~/.bun/bin/bun
  Browsers:
    Chrome: 132.0.6834.160
    Safari: 18.3
  npmPackages:
    @react-router/dev: ^7.1.4 => 7.1.4 
    @react-router/node: ^7.1.4 => 7.1.4 
    @react-router/serve: ^7.1.4 => 7.1.4 
    react-router: ^7.1.4 => 7.1.4 
    vite: ^5.4.11 => 5.4.14

Used Package Manager

npm

Expected Behavior

I expect both Safari and Chrome to have the same behavior when uploading images. The same behavior is defined as is_file rendering as true on the web page and the console.log(...) that fires on form submissions to output the same object.

Actual Behavior

Chrome successfully renders is_file as True and outputs the expected File object on fetcher submission.

Safari renders is_file as False and outputs an empty string on console.log(...) for fetcher submission.

Image of behavior attached:

[moroya]

I am experiencing the same issue on the latest Safari and Mobile Safari.
It seems that this issue occurs only with certain PNG images, not all PNG images.

This Remix issue appears to be related:
remix-run/remix#9044

[plumbdataio]

This bug is still not fixed in the current latest version of 7.5.1, and I hit this with .pdf files.

As moroya mentioned, looks like this is caused by the specific characters in the file name, in my case it was unicode charactors.

So as a workaround, I just renamed the file temporally to alphanumeric only, post it through fetcher.submit() together with original file name, then processed them in the action function.

Hope this helps someone else came here.

[brophdawg11]

This was a tricky one 😂 .

This looks like a bug in Safari when you parse the FormData from a Request using await request.formData(). When the filename has that "narrow no break space" character that OSX screenshots have in it - Safari doesn't receive the file from the request.formData(), but it does for filenames without that character. Both types of filenames work find in Chrome. Based on how Single Fetch is implemented this is effectively what our codepath ends up doing when we create and send the POST /path.data fetch request.

Here's a small stackblitz demonstrating the issue - open the browser console first, and then try choosing a normal file and a file with the special character and clicking the button in both Chrome and Safari and watching the browser console. Only the filename with the special character in Safari will show the second FormData entry incorrectly.

The following code is used to reproduce the issue:

let fd1 = new FormData(document.querySelector('form'));
console.log('First FormData entry:', fd1.get('file'));

let req = new Request('/', { method: 'post', body: fd1 });

// When we parse the formData from the request, Safari no longer has
// the File in it...
let fd2 = await req.formData();
console.log('Second FormData entry:', fd2.get('file'));