How to Extract File Bytes from a Multipart/Form-Data POST Stream in WCF REST?

How to Extract File Bytes from a Multipart/Form-Data POST Stream in WCF REST

When you POST a file to a WCF REST service through a multipart/form-data request, the resulting stream contains a sequence of boundaries, headers, and file bytes. Extracting the file bytes from this stream can be challenging.

Solution: Utilizing Microsoft Public API

Microsoft provides a set of public APIs that simplify this process:

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

Implementation:

This code snippet demonstrates how to extract file bytes using these APIs:

using System.Net.Http;
using System.Net.Http.Formatting;
using System.Threading.Tasks;

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

    var provider = await streamContent.ReadAsMultipartAsync();

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

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

Example Usage:

If you have a WCF REST method, you can implement it as such:

[OperationContract]
[WebInvoke(Method = WebRequestMethods.Http.Post, UriTemplate = "/Upload")]
void Upload(Stream data)
{
    MultipartParser.ParseFiles(
        data,
        WebOperationContext.Current.IncomingRequest.ContentType,
        MyProcessMethod);
}

File Processing:

In the MyProcessMethod you can specify the actions to perform with the extracted file bytes, such as writing them to disk.

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