In C#, HttpClient
is a class provided by the .NET framework that enables you to send HTTP requests and receive HTTP responses. If you want to send custom headers with every request using HttpClient
, you can do so by adding those headers to the DefaultRequestHeaders
property of your HttpClient
instance. This ensures that the specified headers are included in every outgoing request made by that HttpClient
.
Here's an example of how you can achieve this:
using System;
using System.Net.Http;
using System.Threading.Tasks;
class Program
{
static async Task Main(string[] args)
{
using (var httpClient = new HttpClient())
{
// Set up your custom headers to be sent with every request
httpClient.DefaultRequestHeaders.Add("Custom-Header", "HeaderValue");
httpClient.DefaultRequestHeaders.Add("User-Agent", "MyApp/1.0");
// Optionally, you can also set up headers that have multiple values
httpClient.DefaultRequestHeaders.Add("Accept-Language", "en-US");
httpClient.DefaultRequestHeaders.Add("Accept-Language", "en-GB");
// Your target URI
Uri targetUri = new Uri("https://example.com/api/data");
// Send a GET request
HttpResponseMessage response = await httpClient.GetAsync(targetUri);
if (response.IsSuccessStatusCode)
{
string content = await response.Content.ReadAsStringAsync();
Console.WriteLine(content);
}
else
{
Console.WriteLine($"Error: {response.StatusCode}");
}
}
}
}
In this example, we're adding a custom header named Custom-Header
with the value HeaderValue
and setting the User-Agent
to MyApp/1.0
. These headers will be included in the HTTP GET request we're sending to https://example.com/api/data
.
Please note that some headers are considered restricted and cannot be set using DefaultRequestHeaders
. Instead, they need to be set on the request message itself. Here's an example of how you can do that:
using (var httpClient = new HttpClient())
{
// Your target URI
Uri targetUri = new Uri("https://example.com/api/data");
// Create a HttpRequestMessage
using (var request = new HttpRequestMessage(HttpMethod.Get, targetUri))
{
// Add restricted headers directly to the request message
request.Headers.Add("Connection", "keep-alive");
// Send the request
HttpResponseMessage response = await httpClient.SendAsync(request);
if (response.IsSuccessStatusCode)
{
string content = await response.Content.ReadAsStringAsync();
Console.WriteLine(content);
}
else
{
Console.WriteLine($"Error: {response.StatusCode}");
}
}
}
In this example, a Connection
header, which is a restricted header, is being added directly to the HttpRequestMessage
object before sending the request.
It's important to manage the lifetime of HttpClient
correctly. In most cases, it's recommended to use a single instance of HttpClient
for the entire lifetime of the application, which can be achieved by using dependency injection or by creating a static singleton instance. Creating a new HttpClient
instance for each request can lead to socket exhaustion under heavy load.