CSharp Async HttpClient Example

C# Async/Await: Simple HTTP Request with HttpClient

This lesson shows how to use async/await with HttpClient to fetch data from a web API.

Related wiki pages:

• Async basics: CSharp-AsyncAwait-Basics.md
• Tasks and Task.Run: CSharp-Async-Tasks-TaskRun.md
• Exceptions: CSharp-Exceptions-TryCatch.md

Official docs:

• HttpClient: https://learn.microsoft.com/dotnet/api/system.net.http.httpclient

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1. Setup

Create a console app (see CSharp-AsyncAwait-Basics.md), then add this code to Program.cs.

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2. Example: fetch JSON from a web API

using System;
using System.Net.Http;
using System.Threading.Tasks;

class Program
{
    static async Task Main(string[] args)
    {
        try
        {
            string url = "https://jsonplaceholder.typicode.com/todos/1";
            string content = await FetchAsync(url);

            Console.WriteLine("Response content:");
            Console.WriteLine(content);
        }
        catch (HttpRequestException ex)
        {
            Console.WriteLine($"HTTP error: {ex.Message}");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"Unexpected error: {ex.Message}");
        }
    }

    static async Task<string> FetchAsync(string url)
    {
        using var httpClient = new HttpClient();

        using HttpResponseMessage response = await httpClient.GetAsync(url);
        response.EnsureSuccessStatusCode();

        string content = await response.Content.ReadAsStringAsync();
        return content;
    }
}

Key points:

• async Task Main allows await in the entry point.
• HttpClient.GetAsync and ReadAsStringAsync are awaited.
• EnsureSuccessStatusCode throws if the status code is not 2xx.

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3. Next steps

• Modify the URL and inspect different JSON responses.
• Add JSON deserialization using System.Text.Json.
• Combine with exception patterns from CSharp-Exceptions-TryCatch.md.