I’m facing an issue with uploading large files (over several MB) using HttpClient in a MAUI app. While the same server and client code work perfectly in other environments, I’m encountering a 400 Bad Request error when sending larger files from the MAUI app running in a simulator or on an iOS device.

What I’ve Tried:

1. Working Scenarios:

• Windows Console App: Successfully uploads large files.
• Swift App on Mac: Successfully uploads large files.
• Postman: Successfully uploads large files to the server.

2. Problematic Scenarios:

• MAUI Simulator: Uploading files larger than approximately 700 bytes fails with a 400 Bad Request.
• Xamarin iOS App: Similar issue with 400 Bad Request for larger files.

Configuration Details:

• HttpClient Initialization:

var configuration = NSUrlSessionConfiguration.DefaultSessionConfiguration;
configuration.AllowsCellularAccess = true;
configuration.AllowsConstrainedNetworkAccess = true;
configuration.AllowsExpensiveNetworkAccess = true;

var session = new NSUrlSessionHandler(configuration);
var client = new HttpClient(session);

• Multipart Form Upload Example:

public async Task UploadFileAsync(string url, string filePath)
{
    using var client = new HttpClient();
    using var content = new MultipartFormDataContent();
    
    var fileContent = new StreamContent(File.OpenRead(filePath));
    fileContent.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    content.Add(fileContent, "file", Path.GetFileName(filePath));
    
    var response = await client.PostAsync(url, content);
    
    if (response.IsSuccessStatusCode)
    {
        Console.WriteLine("Upload successful!");
    }
    else
    {
        Console.WriteLine($"Error: {response.StatusCode}");
    }
}

• App Transport Security Configuration:

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSExceptionDomains</key>
    <dict>
        <key>mycompany.com</key>
        <dict>
            <key>NSIncludesSubdomains</key>
            <true/>
            <key>NSTemporaryExceptionAllowsInsecureHTTPLoads</key>
            <true/>
            <key>NSTemporaryExceptionMinimumTLSVersion</key>
            <string>TLSv1.3</string>
        </dict>
    </dict>
</dict>

Troubleshooting Steps:

• Configuration Check: Verified that NSUrlSessionConfiguration settings are appropriate for large file uploads.
• File Size Test: Successfully uploading small files but encountering issues with files larger than approximately 1MB.

Questions:

1. What could be causing the 400 Bad Request error specifically for larger files when using HttpClient in a MAUI app?
2. Are there specific configurations or settings in NSUrlSessionHandler or NSUrlSessionConfiguration that I should adjust for handling large file uploads?
3. Could there be any other environmental factors or simulator-specific issues that could be impacting the ability to upload larger files?

Any insights or suggestions would be greatly appreciated!