Consider a web service written in ASP.NET Web API to accept any number files as a 'multipart/mixed' request. The helper method mat look as follows (assuming _client
is an instance of System.Net.Http.HttpClient
):
public T Post<T>(string requestUri, T value, params Stream[] streams)
{
var requestMessage = new HttpRequestMessage();
var objectContent = requestMessage.CreateContent(
value,
MediaTypeHeaderValue.Parse("application/json"),
new MediaTypeFormatter[] {new JsonMediaTypeFormatter()},
new FormatterSelector());
var content = new MultipartContent();
content.Add(objectContent);
foreach (var stream in streams)
{
var streamContent = new StreamContent(stream);
streamContent.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
streamContent.Headers.ContentDisposition =
new ContentDispositionHeaderValue("form-data")
{
Name = "file",
FileName = "mystream.doc"
};
content.Add(streamContent);
}
return _httpClient.PostAsync(requestUri, content)
.ContinueWith(t => t.Result.Content.ReadAsAsync<T>()).Unwrap().Result;
}
The method that accepts the request in the subclass of ApiController has a signature as follows:
public HttpResponseMessage Post(HttpRequestMessage request)
{
/* parse request using MultipartFormDataStreamProvider */
}
Ideally, I'd like to define it like this, where contact, source and target are extracted from the 'multipart/mixed' content based on the 'name' property of the 'Content-Disposition' header.
public HttpResponseMessage Post(Contact contact, Stream source, Stream target)
{
// process contact, source and target
}
However, with my existing signature, posting the data to the server results in an InvalidOperationException
with an error message of:
No 'MediaTypeFormatter' is available to read an object of type
'HttpRequestMessage' with the media type 'multipart/mixed'.
There are a number of examples on the internet how to send and receive files using the ASP.NET Web API and HttpClient. However, I have not found any that show how to deal with this problem.
I started looking at implementing a custom MediaTypeFormatter
and register it with the global configuration. However, while it is easy to deal with serializing XML and JSON in a custom MediaTypeFormatter
, it is unclear how to deal with 'multipart/mixed' requests which can pretty much be anything.
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