ASP.NET Core .NET 8 receives null form values from certain iPhone 13 Pro Max devices

Hello @Ibrahim Akuetiemhe ,

Thank you for sharing the additional results. The affected iPhone sends an empty request (contentLength: 0), so the values are being lost on the client side, before the request reaches ASP.NET Core.
I would suggest starting with the two tests already mentioned in another answer:

1. Send the form with only the text fields. Temporarily comment out the code that appends files. If the text fields arrive correctly, that would help narrow the issue down to the file uploads.
2. Read each file into memory before appending it.

For reference, you can use the following helper and adapt it to your existing upload code.

async function cloneFile(file) {
 const bytes = await file.arrayBuffer();
 return new File([bytes], file.name, { type: file.type });
}
// Inside an async function:
const cloned = await cloneFile(idFile);
formData.append("Identification", cloned);

Apply this to both the identification file and the cover files. If you make buildPolicyFormData() asynchronous, also update its caller. Make sure all file copies have finished before sending the request.

const formData = await buildPolicyFormData();

If arrayBuffer() throws, please share the error message. That would help determine whether reading the selected file is failing. If it succeeds, check whether uploading the cloned files changes the result.

Those would be the two main tests I suggest first. If they do not help narrow it down further, you could also:

• Create a separate minimal FormData request, starting with a hard-coded text field. Then add other values and a small local file one at a time to see when the request becomes empty.
• Check whether the application uses a service worker. If so, temporarily unregister it and test again.
• Clear the website data on the affected iPhone and confirm that both devices are running the same JavaScript version.

Please let me know the results of the two main tests. If you need help with any of the additional checks, feel free to ask.

Still did not work. The request size of the iPhone is 0.5MB which is no way near the request body max size

Hi @Ibrahim Akuetiemhe ,

From your mention of the 0.5 MB upload, I understand “still did not work” to refer to trying the earlier suggestion to increase the request-size limit. Please let me know if you meant a different test.

In any case, submitting without files and trying the in-memory file copies would also help narrow this down. If you have had a chance to try those two tests, could you share what happened with each?

Hello Microsoft Support Team,
I have made significant progress in reproducing the issue and have identified a consistent trigger.

Today's findings:

I have established that the problem is specifically triggered when an image is included in the form submission from the affected iPhone.

My observations are:

When I complete the form and submit it without selecting any image, all the form data reaches the ASP.NET Core backend correctly.

When I select an identification image, all the form fields become null at the backend.

The same behaviour occurs when I select a cover image.

Selecting both identification and cover images also produces the same result.

I also tested several image formats, including PNG, JPEG, HEIC and WebP. The behaviour remained the same across the formats tested: once an image is attached, the backend receives the form fields as null.

This makes it less likely that the issue is specific to a particular image format or codec.

Some optional fields, such as MiddleName and LandMark, are naturally empty. However, even populated and required fields become null when an image is attached.

This is particularly interesting because the issue does not occur when the same form is submitted without an image.

I believe this finding narrows the investigation to how multipart/form-data requests containing binary image files are handled on the affected iPhone/Safari environment.

I will continue investigating and share any additional findings.

Thank you.

@Ibrahim Akuetiemhe Thanks, that's the key result. The text fields arrive without an image and all of them disappear with one, in every format. So Safari fails while reading the image file and then sends the whole body empty. Your server code is fine.

The next test is to read each image into memory yourself before adding it to the form. If Safari can't read the file, this throws an error you can see, instead of silently sending an empty request. Add this function:

async function toInMemoryFile(file) {
  console.log('file', file.name, file.type, file.size, file.lastModified);
  const buffer = await file.arrayBuffer(); // throws here if Safari can't read the file
  return new File([buffer], file.name || 'image.jpg', {
    type: file.type || 'application/octet-stream'
  });
}

Then, wherever you append a file, append the copy instead:

try {
  formData.append('IdentificationImage', await toInMemoryFile(idInput.files[0]));
} catch (err) {
  alert('Could not read image: ' + err.name + ' - ' + err.message);   return; }

On the affected iPhone, there are two possible results:

• The upload now works. The original file reference was going stale between selection and submit (for example, the file input being re-rendered or reset). Keep the in-memory copy as the fix.
• An error appears. Please post the exact err.name and message (for example NotReadableError) and the logged size and type. A size of 0 or a read error points to the photo picker on that device, and testing with a photo taken fresh with the camera vs. one from the library will show which.