How to Accept File POSTs in ASP.NET MVC Web API?

Processing File Uploads in ASP.NET Web API

ASP.NET Web API requires a specific approach for handling file uploads, differing from traditional ASP.NET MVC methods. The HttpPostedFile parameter isn't directly compatible. The solution involves leveraging multipart content.

Multipart Content: The Key to File Uploads

Multipart content is crucial for Web API file uploads. It efficiently combines textual and file data within a single HTTP request.

Building a Controller Action for File Uploads

A controller action using Task<IHttpActionResult> is ideal for asynchronous file processing. Here's an example:

[HttpPost("api/upload")]
public async Task<IHttpActionResult> Upload()
{
    if (!Request.Content.IsMimeMultipartContent())
        throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);

    var provider = new MultipartMemoryStreamProvider();
    await Request.Content.ReadAsMultipartAsync(provider);

    foreach (var file in provider.Contents)
    {
        var filename = file.Headers.ContentDisposition.FileName.Trim('\"');
        var buffer = await file.ReadAsByteArrayAsync();

        // File processing logic here (e.g., save to disk, database, etc.)
    }

    return Ok();
}

Code Explanation:

1. IsMimeMultipartContent(): Verifies the request's multipart content type.
2. MultipartMemoryStreamProvider: Manages the multipart data in memory.
3. ReadAsMultipartAsync(): Parses the multipart data into individual components.
4. File Iteration: The code iterates through each file part, extracting the filename and reading the data into a byte array.
5. File Processing: This is where you'd implement your file handling logic (saving, processing, etc.).
6. Ok(): Returns a successful HTTP response.

Conclusion:

This approach provides a reliable method for handling file uploads in ASP.NET Web API. Using multipart content and MultipartMemoryStreamProvider ensures efficient and robust file upload processing within your Web API services.

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