How to send file download response from ASP.NET Core API controller

Other Questions API
1

Issue

I’m trying to create a file download endpoint in my ASP.NET Core Web API but having trouble getting it to work properly. Instead of downloading the actual file, my API keeps returning JSON data.

Current Implementation

public async Task<HttpResponseMessage> GetFileAsync(string fileId)
{
    var httpResponse = new HttpResponseMessage(HttpStatusCode.OK);
    httpResponse.Content = new StreamContent({{__file_stream_placeholder__}});
    httpResponse.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
    return httpResponse;
}

When I test this endpoint through my browser, it doesn’t trigger a file download. Instead, the API serializes the HttpResponseMessage object to JSON format and sends it back with content-type set to application/json.

What’s the correct way to handle file downloads in ASP.NET Core Web API? I need the browser to actually download the file instead of displaying JSON response.

2

dude, skip HttpResponseMessage - that’s like old school. Just use File(stream, "application/octet-stream", filename) in your action. make sure it returns IActionResult instead, n it should work fine for downloads.

3

You’re encountering this issue because ASP.NET Core serializes HttpResponseMessage to JSON by default. I also faced this challenge when transitioning from Web API 2 to Core. The solution is to utilize FileResult or FileStreamResult instead. For instance, you can return a FileStreamResult like this: return new FileStreamResult(fileStream, "application/octet-stream") { FileDownloadName = "yourfile.ext" };. This approach bypasses JSON serialization as it’s specifically designed for file downloads. Remember to set FileDownloadName for suggested filenames in the browser, and ensure your stream is properly disposed of to prevent memory leaks.

4

It seems like you’re mixing Web API patterns with MVC file handling, which is causing the issue. Avoid using HttpResponseMessage in ASP.NET Core Web API, as the framework automatically manages response serialization. Instead, switch your method to return IActionResult and utilize the built-in File method. For example: public async Task<IActionResult> GetFileAsync(string fileId) { return File(fileStream, "application/octet-stream", "filename.ext"); }. This approach correctly sets the necessary headers and prevents JSON serialization, ensuring proper file downloads.