How to Return Files (e.g., PDFs) from ASP.NET Web API Controllers?

Serving Files from ASP.NET Web API Controllers

While MVC controllers readily use FileContentResult to send files like PDFs, ApiControllers require a different approach. The typical IHttpActionResult return type isn't designed for file delivery.

Addressing Common Pitfalls

Using StreamContent directly often fails, leading to the browser displaying metadata instead of the actual file.

The Effective ByteArrayContent Method

The most reliable method involves converting the file to a byte array and using ByteArrayContent. This ensures proper file delivery.

Code Example: Returning a PDF

This example demonstrates generating and returning a PDF from an ApiController:

[HttpGet]
public HttpResponseMessage Generate()
{
    using (var stream = new MemoryStream())
    {
        // ... PDF generation logic using stream ...

        var result = new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = new ByteArrayContent(stream.ToArray())
        };
        result.Content.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
        {
            FileName = "CertificationCard.pdf"
        };
        result.Content.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");

        return result;
    }
}

This approach guarantees successful file delivery, enabling clients (browsers or other API consumers) to download and view the file correctly.

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