How to create a Client side WebService to call API?

Question

I am working on calling a Web API from MVC5 service using HttpClient . I had first created a MVC Controller and the Get method was working with the HttpClient , but now I have to move the logic into a service class and I am getting errors with async actions and returning a list of books in the Get() method.

Do I need to use HttpWebRequest instead for the service class?

Can someone please assist me in this issue.

API Get()

[HttpGet]    
[Route("api/books")]
public IHttpActionResult Get()
{
    IEnumerable<BookDTO> books;
    books = from b in db.Books
        select new BookDTO()
        {
            Id = b.Id,
            Title = b.Title,
            AuthorName = b.Author.Name
        };
    return Ok(books);
}

Client BookService

HttpClient client;

public IEnumerable<Book> GetBooks()
{
    client.DefaultRequestHeaders.Add("Authorization", "Bearer " + MyToken.myToken);

    HttpResponseMessage responseMessage = client.GetAsync(url).Result;

    if (responseMessage.IsSuccessStatusCode)
    {
        var responseData = responseMessage.Content.ReadAsStringAsync().Result;

        var books = JsonConvert.DeserializeObject<IEnumerable<Book>>(responseData);

        return books;
    }            
}

It is also asking me to have a return after the if body?

Answer 1

You don't have to use a service if you don't want to. it could be a nice way ot package up all your calls to a specific webservice.

As for the compiler error, return something after your if statement.

It could be an empty list.

public IEnumerable<Book> GetBooks()
{
      client.DefaultRequestHeaders.Add("Authorization", "Bearer " + MyToken.myToken);

      HttpResponseMessage responseMessage = client.GetAsync(url).Result;

      if (responseMessage.IsSuccessStatusCode)
      {
         var responseData = responseMessage.Content.ReadAsStringAsync().Result;

         var books = JsonConvert.DeserializeObject<IEnumerable<Book>>(responseData);

         return books;
      }    

      return new List<Book> {};        

}

or you could throw an exception if you want.

Both will satisfy the compiler error.

Answer 2

You should dispose HttpClient object if you no longer need it.

If you use async, the best practice is async all the way back to UI layer . You should not mix blocking and async code.

public async Task<IEnumerable<Book>> GetBooks()
{
    IEnumerable<Book> books = new List<Book>();
    using (HttpClient client = new HttpClient())
    {
        client.DefaultRequestHeaders.Add("Authorization", "Bearer " + MyToken.myToken);
        HttpResponseMessage responseMessage = await client.GetAsync(url);
        if (responseMessage.IsSuccessStatusCode)
        {
            var responseData = await responseMessage.Content.ReadAsStringAsync();
            books = JsonConvert.DeserializeObject<IEnumerable<Book>>(responseData);
        }
    }
    return books;
}

Here is the sample console app if you want to test it.

static void Main(string[] args) => Task.Run(() => MainAsync(args)).Wait();

static async Task MainAsync(string[] args)
{
    var result = await GetResponseFromURI(new Uri("http://www.google.com"));
    Console.WriteLine(result);
    Console.ReadLine();
}

static async Task<string> GetResponseFromURI(Uri u)
{
    var response = "";
    using (var client = new HttpClient())
    {
        HttpResponseMessage result = await client.GetAsync(u);
        if (result.IsSuccessStatusCode)
        {
            response = await result.Content.ReadAsStringAsync();
        }
    }
    return response;
}