如果您的API方法期望使用，HttpRequestMessage则可以从中提取流：

public HttpResponseMessage Put(HttpRequestMessage request)
{
    var stream = GetStreamFromUploadedFile(request);

    // do something with the stream, then return something
}

private static Stream GetStreamFromUploadedFile(HttpRequestMessage request)
{
    // Awaiting these tasks in the usual manner was deadlocking the thread for some reason.
    // So for now we're invoking a Task and explicitly creating a new thread.
    // See here: http://stackoverflow.com/q/15201255/328193
    IEnumerable<HttpContent> parts = null;
    Task.Factory
        .StartNew(() => parts = request.Content.ReadAsMultipartAsync().Result.Contents,
                        CancellationToken.None,
                        TaskCreationOptions.LongRunning,
                        TaskScheduler.Default)
        .Wait();

    Stream stream = null;
    Task.Factory
        .StartNew(() => stream = parts.First().ReadAsStreamAsync().Result,
                        CancellationToken.None,
                        TaskCreationOptions.LongRunning,
                        TaskScheduler.Default)
        .Wait();
    return stream;
}

当使用张贴HTTP表单时，这对我有用enctype="multipart/form-data"。