Consuming ASP.NET Core 2.0 Web API Using HttpClient

Problem

How to consume ASP.NET Core Web API using HttpClient.

Solution

We’ll create a library to wrap the functionality of HttpClient. I’ll use builder pattern for this purpose. Add a class with methods for storing the parts of HttpClient.

public class HttpRequestBuilder
{
      private HttpMethod method = null;
      private string requestUri = "";
      private HttpContent content = null;
      private string bearerToken = "";
      private string acceptHeader = "application/json";
      private TimeSpan timeout = new TimeSpan(0, 0, 15);

      public HttpRequestBuilder()
      {
      }

      public HttpRequestBuilder AddMethod(HttpMethod method)
      {
          this.method = method;
          return this;
      }

      public HttpRequestBuilder AddRequestUri(string requestUri)
      {
          this.requestUri = requestUri;
          return this;
      }

      public HttpRequestBuilder AddContent(HttpContent content)
      {
          this.content = content;
          return this;
      }

      public HttpRequestBuilder AddBearerToken(string bearerToken)
      {
          this.bearerToken = bearerToken;
          return this;
      }

      public HttpRequestBuilder AddAcceptHeader(string acceptHeader)
      {
          this.acceptHeader = acceptHeader;
          return this;
      }

      public HttpRequestBuilder AddTimeout(TimeSpan timeout)
      {
          this.timeout = timeout;
          return this;
      }
 rest of code

Add a method to send a request using HttpClient and get the response.

public async Task<HttpResponseMessage> SendAsync()
{
    // Check required arguments
    EnsureArguments();

    // Setup request
    var request = new HttpRequestMessage
    {
       Method = this.method,
       RequestUri = new Uri(this.requestUri)
    };

    if (this.content != null)
       request.Content = this.content;

    if (!string.IsNullOrEmpty(this.bearerToken))
        request.Headers.Authorization =
          new AuthenticationHeaderValue("Bearer", this.bearerToken);

       request.Headers.Accept.Clear();
    if (!string.IsNullOrEmpty(this.acceptHeader))
        request.Headers.Accept.Add(
           new MediaTypeWithQualityHeaderValue(this.acceptHeader));

    // Setup client
    var client = new System.Net.Http.HttpClient();
    client.Timeout = this.timeout;

    return await client.SendAsync(request);
}

We’ll also add a factory class to build requests for GET, POST, PUT, PATCH, and DELETE.

public static class HttpRequestFactory
{
      public static async Task<HttpResponseMessage> Get(string requestUri)
      {
          var builder = new HttpRequestBuilder()
                              .AddMethod(HttpMethod.Get)
                              .AddRequestUri(requestUri);

          return await builder.SendAsync();
      }

      public static async Task<HttpResponseMessage> Post(
         string requestUri, object value)
      {
          var builder = new HttpRequestBuilder()
                              .AddMethod(HttpMethod.Post)
                              .AddRequestUri(requestUri)
                              .AddContent(new JsonContent(value)) ;

          return await builder.SendAsync();
      }

      public static async Task<HttpResponseMessage> Put(
         string requestUri, object value)
      {
          var builder = new HttpRequestBuilder()
                              .AddMethod(HttpMethod.Put)
                              .AddRequestUri(requestUri)
                              .AddContent(new JsonContent(value));

          return await builder.SendAsync();
      }

      public static async Task<HttpResponseMessage> Patch(
         string requestUri, object value)
      {
          var builder = new HttpRequestBuilder()
                              .AddMethod(new HttpMethod("PATCH"))
                              .AddRequestUri(requestUri)
                              .AddContent(new PatchContent(value));

          return await builder.SendAsync();
      }

      public static async Task<HttpResponseMessage> Delete(string requestUri)
      {
          var builder = new HttpRequestBuilder()
                              .AddMethod(HttpMethod.Delete)
                              .AddRequestUri(requestUri);

          return await builder.SendAsync();
      }
}

JsonContent, PatchContent, and FileContent are custom classes to simplify the sending of data.

public class JsonContent : StringContent
{
     public JsonContent(object value)
         : base (JsonConvert.SerializeObject(value), Encoding.UTF8, "application/json")
     {
     }

     public JsonContent(object value, string mediaType)
         : base(JsonConvert.SerializeObject(value), Encoding.UTF8, mediaType)
     {
     }
 }

 public class PatchContent : StringContent
 {
     public PatchContent(object value)
         : base (JsonConvert.SerializeObject(value), Encoding.UTF8,
                   "application/json-patch+json")
     {
     }
 }

 public class FileContent : MultipartFormDataContent
 {
     public FileContent(string filePath, string apiParamName)
     {
         var filestream = File.Open(filePath, FileMode.Open);
         var filename = Path.GetFileName(filePath);

         Add(new StreamContent(filestream), apiParamName, filename);
     }
}

Finally, a few extension methods to help working with HttpResponseMessage class.

public static class HttpResponseExtensions
{
     public static T ContentAsType<T>(this HttpResponseMessage response)
     {
         var data = response.Content.ReadAsStringAsync().Result;
         return string.IsNullOrEmpty(data) ?
                         default(T) :
                         JsonConvert.DeserializeObject<T>(data);
     }

     public static string ContentAsJson(this HttpResponseMessage response)
     {
         var data = response.Content.ReadAsStringAsync().Result;
         return JsonConvert.SerializeObject(data);
     }

     public static string ContentAsString(this HttpResponseMessage response)
     {
         return response.Content.ReadAsStringAsync().Result;
     }
}

We can use the code above like -

private static async Task GetList()
{
     var requestUri = $"{baseUri}";
     var response = await HttpRequestFactory.Get(requestUri);

     Console.WriteLine($"Status: {response.StatusCode}");
     var outputModel = response.ContentAsType<List<MovieOutputModel>>();
     outputModel.ForEach(item =>
                     Console.WriteLine("{0} - {1}", item.Id, item.Title));
}

Here is how the sample client looks like.

Note
The sample code has examples of another type of requests too. It uses CRUD API created in a previous post. Download its project and run the API before running this console sample.

Source Code

GitHub