ASP .Net Web API pass object

Question

Well I have a small test applicationn a .NET Web API and a library for both sharing some classes.

My goal is to pass a object via POST request to the api.

This is how my program looks like:

var metadata = new Metadata(); // Metadata is a empty class in my library

try
{
    var postData = ByteConverter.ObjectToByteArray(metadata); // ByteConverter.ObjectToByteArray is method in my library to convert objects to a byte array

    var request =
        (HttpWebRequest)WebRequest.Create("http://localhost:65160/test");

    request.Method = "POST";
    request.ContentType = "application/json";
    request.ContentLength = postData.Length;

    using (var stream = request.GetRequestStream())
    {
        stream.Write(postData, 0, postData.Length);
    }

    await request.GetResponseAsync();
}
catch (Exception ex)
{
    // ignored
}

And this is how the POST method of my api looks like:

[HttpPost]
public HttpResponseMessage Test([FromBody] Metadata metadata)
{
    return Request.CreateResponse(HttpStatusCode.OK);
}

The method of my api is called but the metadata param is always null. What do I have to change to make it work?

Edit:

As requested:

public static byte[] ObjectToByteArray(object obj)
{
    if(obj == null)
        throw new ArgumentNullException($"The parameter {nameof(obj)} can't be null");

    try
    {
        var bf = new BinaryFormatter();
        using (var ms = new MemoryStream())
        {
            bf.Serialize(ms, obj);
            return ms.ToArray();
        }
    }
    catch (SerializationException)
    {
        throw;
    }
    catch
    {
        return new byte[0];
    }
}

To understand the reason, I think, you should first use http listener like Fiddler2 to see what is the data in the body of the request. — ali
– ali, Commented May 26, 2016 at 10:37
I do not understand what ByteConverter.ObjectToByteArray does: I hope it serializes your object into JSON and only then returns the resulting text as a byte array. Am I right? Can you post the implementation? — Federico Dipuma
– Federico Dipuma, Commented May 26, 2016 at 12:51
You set the header of the request as json. That means that you need to convert the metadata to JSON string representation of the object then convert it to bytes. Are you able to use HttpClient or are you restricted to using WebClient? — Nkosi
– Nkosi, Commented May 26, 2016 at 13:14

Federico Dipuma · Accepted Answer · 2016-05-26 13:25:37Z

2

You are trying to send data to your API in binary format but, of course, your API will expect a JSON body (you even declared application/json as Content-Type). This could never work.

If you want to keep your code as is you will need to serialize your object into JSON before writing the request body inside your method. To achieve this you should really use a library like Json.NET (installing it using this NuGet package).

Here it is a small sample:

public static byte[] ObjectToByteArray(object obj)
{
    if(obj == null)
        throw new ArgumentNullException($"The parameter {nameof(obj)} can't be null");

    var json = JsonConvert.SerializeObject(obj);

    var bytes = Encoding.UTF8.GetBytes(json);

    return bytes;
}

While this should work, I strongly suggest you to avoid doing all this by hand and use HttpClient as stated in other answer, or (even better) a full REST client library like Rest Sharp.

answered May 26, 2016 at 13:25

Federico Dipuma

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1 Comment

Christian Klemm Over a year ago

I just had a look at Rest Sharp and I think I will use it. Thank you!

Artavazd Balayan · Accepted Answer · 2016-05-26 11:02:39Z

0

I'm using HttpClient and haven't got any problem with it. Need to add nuget package System.Net.Http.Formatting. PostAsJsonAsync is part of HttpClientExtensions. Here is example code:

using System.Net.Http;
// ....

using (var client = new HttpClient())
{
      string url = "http://localhost:65160/test"; // <= set valid URL
      var metadata = new Metadata();

      client.DefaultRequestHeaders.Accept.Clear();
      client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
      var response = await client.PostAsJsonAsync(url, metadata);
      response.EnsureSuccessStatusCode();
}

edited May 26, 2016 at 11:02

answered May 26, 2016 at 10:37

Artavazd Balayan

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3 Comments

Christian Klemm Over a year ago

This code can't work as PostAsJsonAsync is a static method.

Artavazd Balayan Over a year ago

Yes, you're right. You also need System.Net.Http.Formatting - nuget.org/packages/System.Net.Http.Formatting.Extension

Nkosi Over a year ago

@chris579 PostAsJsonAsync is an extension method targeting the HttpClient class. That is why it is static.

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