How Can I Return a File as a Binary Response in ASP.Net Core Web API?

Overcoming the JSON-Converted File Return Issue in ASP.Net Core Web API

In ASP.Net Core Web API, returning a file as a JSON response can be troublesome. Understandably, you'd want to return the file in its original binary format. To resolve this issue, we need to delve into the concept of result types in ASP.Net Core.

Understanding the IActionResult Interface

In ASP.Net Core, IActionResult is an interface representing the result of an action method. It encapsulates the HTTP response body and status code, providing flexibility in customizing the response.

Solution: Returning a FileStreamResult

To return a file, we'll leverage the FileStreamResult class, which implements IActionResult. This allows us to specify the file stream, content type, and filename for the response.

The following code snippet demonstrates this approach:

<code class="csharp">[Route("api/[controller]")]
public class DownloadController : Controller
{
    [HttpGet("{id}")]
    public async Task<IActionResult> Download(string id)
    {
        Stream stream = await // Get stream based on id here

        if (stream == null)
            return NotFound(); // Handle not found scenario

        return File(stream, "application/octet-stream", "filename.ext");
    }
}</code>

In this code:

• File() creates a FileStreamResult with the specified stream, content type, and filename.
• The framework automatically sets the HTTP response status code to 200 OK.
• The framework disposes of the stream when the response is complete to avoid exceptions.

Note:

• If you use a using statement on the stream within the Download method, the stream may be disposed before the response is sent, leading to an error.
• The NotFound() call returns an NotFoundResult with an HTTP status code of 404 Not Found.

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