How to send a file as response in ASP.NET Core Web API?

Other Questions API
1

I’m struggling with sending files through my ASP.NET Core Web API. My current setup returns the HttpResponseMessage as JSON instead of the actual file. Here’s what I’ve tried:

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

When I hit this endpoint in my browser, I get a JSON representation of the HttpResponseMessage instead of the file download. The Content-Type header is set to application/json. How can I fix this to properly send the file to the client? Any help would be great!

2

I encountered a similar issue in one of my projects. The problem lies in how ASP.NET Core handles HttpResponseMessage. Instead, use FileResult for file downloads. Here’s a modified version of your code that should work:

public FileResult GetFile(string fileId)
{
    var fileStream = // Your file stream logic here
    string fileName = "yourFileName.ext"; // Set the desired file name
    string contentType = "application/octet-stream"; // Or the appropriate MIME type

    return File(fileStream, contentType, fileName);
}

This approach leverages ASP.NET Core’s built-in file handling, ensuring the correct content type and prompting a download in the browser. Remember to dispose of your file stream properly if needed.

3

hey mandy, i’ve had this issue before. try using IActionResult instead of HttpResponseMessage. something like:

public IActionResult GetFile(string fileId)
{
    var fileStream = /* get your file stream */;
    return File(fileStream, "application/octet-stream", "filename.ext");
}

this should work better for sending files. hope it helps!

4

As someone who’s been working with ASP.NET Core for a while, I can tell you that sending files can be tricky. I’ve found that using PhysicalFileResult works great for this. Here’s what I do:

[HttpGet("download/{fileId}")]
public IActionResult DownloadFile(string fileId)
{
    var filePath = Path.Combine(_environment.ContentRootPath, "Files", fileId);
    if (!System.IO.File.Exists(filePath))
        return NotFound();

    var fileName = Path.GetFileName(filePath);
    var mimeType = "application/octet-stream";

    return PhysicalFile(filePath, mimeType, fileName);
}

This approach has several advantages. It’s efficient because it streams the file directly from disk, works with large files, and automatically sets the correct headers. Just make sure your file storage location is secure. Also, consider adding authorization if needed.