How to Efficiently Extract File Bytes from a Multipart/Form-Data POST Request Stream?

Multipart/Form-Data POST and File Input Streaming

Question:

When posting a file to a REST service using multipart/form-data, how can the file bytes be efficiently extracted from the request stream for processing?

Answer:

To extract file bytes from a multipart/form-data POST request stream, a comprehensive approach using Microsoft public APIs is available.

Prerequisites:

• System.Net.Http.dll (included in .NET 4.5 or via NuGet for .NET 4)
• System.Net.Http.Formatting.dll (via NuGet for .NET 4.5 or .NET 4)

Code Implementation:

public static async Task ParseFiles(
    Stream data, string contentType, Action<string, Stream> fileProcessor)
{
    // Parse multipart request content
    var streamContent = new StreamContent(data);
    streamContent.Headers.ContentType = MediaTypeHeaderValue.Parse(contentType);
    var provider = await streamContent.ReadAsMultipartAsync();

    // Iterate through file parts
    foreach (var httpContent in provider.Contents)
    {
        var fileName = httpContent.Headers.ContentDisposition.FileName;
        if (string.IsNullOrWhiteSpace(fileName)) continue;

        using (Stream fileContents = await httpContent.ReadAsStreamAsync())
        {
            // Process file bytes
            fileProcessor(fileName, fileContents);
        }
    }
}

Sample Usage:

For a WCF REST method "OperationContract", you can implement the file processing:

public void Upload(Stream data)
{
    MultipartParser.ParseFiles(
           data, 
           WebOperationContext.Current.IncomingRequest.ContentType, 
           MyProcessMethod);
}

By utilizing this approach, developers can effortlessly retrieve file bytes from multipart/form-data POST requests for subsequent processing and storage.

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