Handling Range Requests in .NET 9 Behind Azure Front Door

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When deploying a .NET 9 application behind Azure Front Door with response compression enabled, you might encounter unexpected issues with static files, such as HTTP 416 Range Not Satisfiable errors. These arise because Front Door often sends byte-range requests for optimization, which your application may not handle properly by default.

To address this, you can configure your app to remove incoming Range headers and explicitly communicate that range requests are not supported by adding the Accept-Ranges: none header to all responses.

Code to Fix Range Request Issues

Place this middleware before any static file handling code in your Program.cs:

// Middleware to remove "Range" headers from requests
app.Use(async (context, next) =>
{
    if (context.Request.Headers.ContainsKey("Range"))
    {
        context.Request.Headers.Remove("Range");
    }
    await next();
});

// Middleware to add "Accept-Ranges: none" in responses
app.Use(async (context, next) =>
{
    await next();
    context.Response.Headers["Accept-Ranges"] = "none";
});

Why This Is Needed

When compression is enabled in Azure Front Door, it may send range requests to optimize bandwidth. However, if your app does not properly support or handle range requests, it can result in errors for static files.

• What the code does:
  • Removes the Range header from incoming requests to prevent partial content handling.
  • Adds the Accept-Ranges: none header to responses, telling clients that range requests are not supported.
• Why it matters:
  • Ensures smooth file delivery without unnecessary errors.
  • Helps maintain compatibility with Front Door’s caching and compression optimizations.

Where to Place It

The placement of this middleware is crucial:

1. Before Static File Middleware: It must come before any call to app.UseStaticFiles() so that static file handling bypasses range processing entirely.
2. General Structure:

   app.Use(async (context, next) =>
   {
       // Remove Range header
   });

   app.Use(async (context, next) =>
   {
       // Add Accept-Ranges header
   });

   // Static file handling (generic or ABP-specific)
   app.UseStaticFiles();

When You Don’t Need This

If compression is disabled in Azure Front Door or your app doesn’t rely on static files, this fix may not be necessary. But when compression is active, this small adjustment ensures seamless compatibility.

By handling this proactively, you can avoid frustrating issues in production environments. Happy coding! 🚀

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