How to correctly use PostAsync and PutAsync?

Hi Everyone,

I'm trying to setup an API for my BLL and I got GET and DELETE actions working fine. Now I'm trying to submit data back to the API with PUT but I can't get it to work. Specifically, I'm using HttpClient as the client to talk to Web API.

Here is the code I'm using which just hangs:

public string Put<T>(T data)
{
    using (var httpClient = new HttpClient())
    {
        var mediaType = new MediaTypeHeaderValue("application/json");
        var jsonSerializerSettings = new JsonSerializerSettings();
        var jsonFormatter = new JsonNetFormatter(jsonSerializerSettings);
 
        var requestMessage = new HttpRequestMessage<T>(data, mediaType, new MediaTypeFormatter[] { jsonFormatter });
 
        var result = httpClient.PutAsync(_endpoint, requestMessage.Content).Result;
 
        return result.Content.ReadAsStringAsync().Result;
    }
}

Re: How to correctly use PostAsync and PutAsync?

I would encourage you to go and have a look at C# Async CTP. You can get it today and build apps with it. It has go-live licence as well and C# 5 will have the features inside that CTP.

With async CTP, you will be able to write asyncronous code just like you write your syncronous code. I am not a good enough on that to give samples but you can do the following AFAIK:

var result = await httpClient.PutAsync(_endpoint, requestMessage.Content);
        return await result.Content.ReadAsStringAsync();

Re: How to correctly use PostAsync and PutAsync?

First of all, are generic methods supported in the Web API? I think I read somewhere they currently are not?

What are you trying to accomplish with the method btw? You are accepting a generic class then formatting it into a json string. Why not just use JsonValue? What kind of data are you doing a PUT with btw?

But heres a modified example of how you can leverage async today, but I wrote the example without the generic support.
The trick is to make the API method return a Task, then you are not blocking the request thread when waiting for the client to finish.

public Task<string> Put(string data)
{
  var mediaType = new MediaTypeHeaderValue("application/json");
  var jsonSerializerSettings = new JsonSerializerSettings();
  var jsonFormatter = new JsonNetFormatter(jsonSerializerSettings);
  var requestMessage = new HttpRequestMessage<T>(data, mediaType, new MediaTypeFormatter[] { jsonFormatter });
  var httpClient = new HttpClient()

  return httpClient.PutAsync(_endpoint, requestMessage.Content).ContinueWith(httpResponseMessage =>
  {
    return httpResponseMessage.Result.Content.ReadAsStringAsync();
  });
}

Re: How to correctly use PostAsync and PutAsync?

Thanks for the replies guys, but I think that my problem is not with sync/async.

I would love to use the new await keyword, but right now, I don't want to be building against the .NET 4.5 Developer Preview.

Back to the issue.

Even if my code was blocking the thread until the response was returned, the code would still continue (eventually). I'm posting to a local Web API service on another port, and my GET and DELETE actions are instantaneous. So something is fundamentally wrong with my code, causing it to hang. I think it's on the client end, because I'm pretty sure the request never actually hits the service on the other end.

All I'm trying to do is serialize a POCO and PUT it to the Web API to update a record in a database. My put handler in the Web API controller looks like this:

[HttpPut]
public void PutMyClass(int id, MyClass myClass)
{
    myClass.MyClassID = id;
 
    if (!_myClassRepository.UpdateMyClass(myClass))
    {
        throw new HttpResponseException(HttpStatusCode.NotFound);
    }
}

Any other ideas?

Re: How to correctly use PostAsync and PutAsync?

So the API you showed in your first post is functioning as a kind of reverse proxy?

What are you serializing your POCO as when posting? If it's JSON, then instead of a generic method just use JsonValue and send that on to your backend service?

Try changing your method to not be generic, people have had problems with generic methods on a controller:
http://forums.asp.net/t/1770829.aspx/1?Using+generics+in+ApiController+controller+

Re: How to correctly use PostAsync and PutAsync?

Thanks for another reply SiggiGG.

I don't think generics are my problem. I tried removing all the generic code and just doing a post to the service and it still hangs.

I also tried re-including the async code (in .NET 4), and I still have the same problem.

Can you elaborate on the JsonValue mechanism you mentioned?

Re: How to correctly use PostAsync and PutAsync?

skippyfire

Thanks for another reply SiggiGG.

I don't think generics are my problem. I tried removing all the generic code and just doing a post to the service and it still hangs.

I also tried re-including the async code (in .NET 4), and I still have the same problem.

Can you elaborate on the JsonValue mechanism you mentioned?

Are you using the JsonNetFormatter from here?

http://code.msdn.microsoft.com/Using-JSONNET-with-ASPNET-b2423706

If Yes, then there seems to be a problem in the WriteToStreamAsync method of this formatter. I was able to repro this issue. This method seems to work fine while writing the response on the Service side, but has problems writing on the Client side. I have notified Henrik regarding this. Will post updates.

[UPDATE] : The blog has been updated with the fix to the JsonNetFormatter. You should be able to use it now.

Re: How to correctly use PostAsync and PutAsync?

skippyfire
Can you elaborate on the JsonValue mechanism you mentioned?

JsonValue is a really handy type to deal with JSON data in a loosely typed way.

In your case you can do something like this:

public void Post(JsonValue value)
{
    var httpClient = new HttpClient();
    httpClient.BaseAddress = new Uri("http://localhost:31724");
    StringContent content = new System.Net.Http.StringContent(value.ToString(), Encoding.UTF8, "application/json");
    var result = httpClient.PutAsync("api/Values", content).Result;
}

Re: How to correctly use PostAsync and PutAsync?

Stupid question: How do I new up a JsonValue?

It looks like the constructor(s) are not public and I don't see any static methods that would let me "load" a JsonValue from a concrete POCO.

Is JsonObject what I want instead?

Re: How to correctly use PostAsync and PutAsync?

You can use JsonValue.Parse(string json) to create a new instance.

Just curious, why do you need to new up a JsonValue? When posting data you can just post normal POCO classes. I was just showing you how to use JsonValue to receive loosely typed data.

Re: How to correctly use PostAsync and PutAsync?

Sorry, I don't think I explained it well.

I have a Project that acts as my client for the service. So multiple front ends can reference the same client project.

The client project will take data from MVC, WinForms, WPF, whatever, and post the data for you. So the client project takes a POCO, and posts it to the Web API.

For now, I'm not posting data from a web page directly to the service. That is why I'm using PostAsync and PutAsync. I'm using those to send data to the Web API service. I really don't care how the data is serialized, I was just trying to use a JSON one in this case.

Is my problem more clear now? Should I be using HttpClient to post/put data like this? Or is there something easier I can/should use, at least until the Web API is more baked?

Re: How to correctly use PostAsync and PutAsync?

Ah ok that explains it :) I thought you had a "front end" Web API that was re-posting data to a backend one (I assumed for some security reasons). Now the generic code makes more sense ;)

And yes you should absolutely use HttpClient to interect with Web APIs, it's a great client.

If you debug your client code, where is it hanging? Is the URL in your _endpoint variable correct?

There are a few ways to encode a POCO object into JSON for PUT/POST, and afaik your method of using the HttpRequestMessage should work.
You can also use StringContent or StreamContent, and a Json serializer to encode your class.

Re: How to correctly use PostAsync and PutAsync?

It hangs when it is trying to get the result from the request.

My endpoint is valid for GETs and DELETEs.

Not sure what else it could be. Has anyone posted any sample for making POST and PUT requests FROM the Web API?

Re: How to correctly use PostAsync and PutAsync?

I think you missed my post in this discussion thread: http://forums.asp.net/post/4847638.aspx

Re: How to correctly use PostAsync and PutAsync?

FYI, I did try this from a simple HTML page with some jQuery, and I was able to make a PUT request. So the problem is definitely client side for me.

Re: How to correctly use PostAsync and PutAsync?

Interesting. Please try using a StringContent or StreamContent class instead of the HttpRequestMessage you are doing.

Re: How to correctly use PostAsync and PutAsync?

SkippyFire, I have posted the reason behind the issue here: http://forums.asp.net/post/4847638.aspx

Re: How to correctly use PostAsync and PutAsync?

Hi Kiran,

Yes I did miss that, twice apparently! Thank you for pointing it out to me again. I'm going to try reverting to the default Formatter and see if that works.

Thanks again.

Re: How to correctly use PostAsync and PutAsync?

I have simillar issues :

I have code like this on serverSide :

public HttpResponseMessage<Contact> Post(HttpRequestMessage<Contact> request)
        {
            var pero = request.Content.ReadAsAsync(typeof(Contact)).Result;

Problem is that pero variable is always null

Re: How to correctly use PostAsync and PutAsync?

logic_rabbit

I have simillar issues :

I have code like this on serverSide :
public HttpResponseMessage<Contact> Post(HttpRequestMessage<Contact> request)
        {
            var pero = request.Content.ReadAsAsync(typeof(Contact)).Result;
Problem is that pero variable is always null

logic_rabbit, you can acutally get the request from the ApiController instance:

  public HttpResponseMessage<Contact> Post()
        {
            var pero = this.Request.Content.ReadAsAsync(typeof(Contact)).Result;