Develop Reference

HttpClient changing request URI when called from WebAPI

I am implementing a transparent server-side proxy for an ASP.NET MVC application which wants to communicate with an API on another server; the code is fairly straightforward:
public class TransparentProxyDelegatingHandler : DelegatingHandler
{
private static readonly Uri ApiUri;
private static readonly HttpClient Client;
static TransparentProxyDelegatingHandler()
{
var apiServer = new Uri(ConfigurationManager.AppSettings["ApiUrl"]);
ApiUri = new Uri(apiServer);
Client = new HttpClient();
}
protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
request.Headers.Add("X-Forwarded-For", request.GetClientIpAddress());
request.RequestUri = TranslateIncomingRequestToUpstreamApi(request);
request.Headers.AcceptEncoding.Clear();
var response = await Client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, cancellationToken);
return response;
}
private static Uri TranslateIncomingRequestToUpstreamApi(HttpRequestMessage request)
{
var forwardUri = new UriBuilder(request.RequestUri)
{
Host = ApiUri.Host,
Path = request.RequestUri.AbsolutePath.Replace("/Proxy", string.Empty)
};
return forwardUri.Uri;
}
}
So if I query GET https://ui.myserver.com/proxy/timesheets?from=2018-01-01, the request URI gets changed by the proxy to GET https://api.myserver.com/timesheets?from=2018-01-01, and I can verify this in the debugger; however, when the SendAsync method is invoked, the hostname part of the request URI is changed back to https://ui.myserver.com, and the call fails.
Why is it changing the value of request.RequestUri when I call SendAsync ? I've checked the source in GitHub (https://github.com/dotnet/corefx/blob/master/src/System.Net.Http/src/System/Net/Http/HttpClient.cs), but none of the conditions for changing the value seem to apply in my case. Unfortunately the GitHub source does not align with the debug symbols, so I can't seem to step into the HttpClient source to figure out what's really going on.

OK, I found the cause of my problem; I needed to set change the Host header; the initial request to the proxy set it to the hostname of the UI (ui.myserver.com), and that overrides the hostname of the proxy that was set in the request. So if I add the following:
request.Headers.Host = $"{ApiUri.Host}:{ApiUri.Port}";
then everything magically works.

Post to HTTP and get JSON response back in c#

I am trying to write call a web page that then posts to a web service that outputs a JSON file.
The problem I have is that the GetAsync returns a null value for response. This in turn doesn't provide the proper URL for call back for the GetTestResultAsync method.
Here's my code:
static HttpClient client = new HttpClient();
static async Task RunAsync()
{
// New code:
client.BaseAddress = new Uri("http://10.1.10.10:8080/");
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
try
{
Uri url = await CallTestAsync();
string response = await GetTestResultAsync(url.PathAndQuery);
Console.WriteLine(response);
}
catch (Exception e)
{
Console.WriteLine(e);
}
}
static async Task<Uri> CallTestAsync()
{
HttpResponseMessage response = await client.GetAsync("test.html");
response.EnsureSuccessStatusCode();
// return URI of the created resource.
return response.Headers.Location;
}
static async Task<string> GetTestResultAsync(string path)
{
HttpResponseMessage response = await client.GetAsync(path);
string streamResponse = string.Empty;
if (response.IsSuccessStatusCode)
{
streamResponse = await response.Content.ReadAsStringAsync();
}
return streamResponse;
}
static void Main(string[] args)
{
RunAsync().Wait();
}

HttpClient by default will automatically redirect 3xx responses, which means that the response you get when calling GetAsync will not have the Location header as it would have already redirected to the proper location.
To override this behaviour you have to provide an HttpMessageHandler with this feature disabled. For example:
static HttpClientHandler handler = new HttpClientHandler { AllowAutoRedirect = false };
static HttpClient client = new HttpClient(handler);
The important part here being setting the handler's AllowAutoRedirect to false.
Important: By overriding the default behaviour for redirect responses you'll have to handle any 3xx manually, which might add unnecessary work for you as in many cases the default behaviour is sufficient. If you were to leave it as is, it'd already make the 2nd request that you're doing, for you.
Also note that a 3xx response is not a success response, which means that if you don't use the auto-redirect feature when you call response.EnsureSuccessStatusCode(); it'll throw an exception.
Furthermore, although most servers are quite forgiving when it comes to headers such as the Accept header, you are most likely using the wrong one in this case as an HTML page should be a text/html rather than an application/json (which should be used when expecting a JSON object as a response).

HttpClient is modifying my original request to change domains

I have some code that is making a Server2Server call using an HttpClient. Here is some quick code
Code to make a request
private HttpRequestMessage GetRequest(Uri uri, NameValueCollection headers)
{
var method = HttpMethod.Get;
var request = new HttpRequestMessage(method, uri);
foreach (string v in headers)
{
var success = request.Headers.TryAddWithoutValidation(v, headers[v]);
if (!success)
{
// log something ( no logs are appearing )
}
}
return request;
}
Code to make the request
private void AsyncCallUrl(Uri url, NameValueCollection headers)
{
object result1 = null;
var handler = new HttpClientHandler() { AllowAutoRedirect = false };
using (HttpClient client = new HttpClient(handler))
{
var request = GetRequest(url, headers);
using (HttpResponseMessage response = client.SendAsync(request).Result) // when this line is executed the request object's domain is changed to something else
{
using (HttpContent content = response.Content)
{
result1 = content.ReadAsStringAsync().Result;
}
}
}
I've verified that the request object is created appropriately with the proper domain. I've also verified that the network traffic is going to the wrong domain, even the request object shows the new bad domain. What I don't is why this is happening. I've even set the AllowAutoRedirect to false
NOTE: As a note I notice that if I use GetAsync instead of SendAsync the domain change doesn't happen. However this is not an ideal solution as in order to add headers I would need to add them to the HttpClient itself and this code lives on an IIS server and I don't want to make a new client for every request

So, with SendAsync the value of the Host header of the request is determined by the uri parameter... However it is possible to override the Host header through the Headers property of the request.
It's highly likely that the NameValueCollection headers that you are blindly injecting into the request's headers contains an entry for Host which is different to that which you supplied in the Uri.
As an aside, this behaviour can be useful, if (for instance) you were to discover that the DNS performance of HttpWebRequest (the business end of HttpClient on Windows) is sub-standard. I've bypassed .Net/Windows DNS by using a third party library to look up the IP of the host, rewriting the Uri to use the IP address in place of the host name, then setting the Host header on the outgoing request back to the original host name.

Rapid web requests to many different websites using HttpClient C#

My team maintains a tool that is responsible for doing rapid verification of over 1000 different client websites. The tool is a Windows Service (.NET 4.5.2, C#) that reads requests from a queue, and executes a 'health check' for each request. It usually handles over 500 requests a minute, but can be responsible for more. Each request takes a second or two to execute.
A request contains a Uri and credentials needed for doing the health check. A health check is a POST against the AUTH page with the credentials (the app has custom auth, it's not header based auth), and then a GET to the home page, with a quick verification that it's the home page we expect. It then goes to a status page in the application, and does some quick checks against that. The GET requests have to use the cookies from the Set-Cookie header in the auth post.
We've been having performance problems with the tool as it scales. It currently creates a new HttpWebRequest object for each post and get in the process. There is a shared CookieContainer that is populated by the first post, so that we can get to the home page and then the status page.
I want to change this service to use the HttpClient object available in .NET 4.5. The problem is everywhere I read online says you want to avoid rapid creation and destruction of HttpClients. You'd rather keep one instance alive for the lifetime of the application. The problem I have is that HttpClient seems to work really well against one endpoint, not many.
I have looked into several options, and am not sure which is best to proceed:
Create a new HttpClient for each request, and use it for the duration of that request. That means it will live for a couple seconds, and be used for 3 calls. This would not be easy to implement, but I'm concerned about the overhead of creating and destroying hundreds of HttpClients a minute.
Figure out if it's possible to use one HttpClient instance for different endpoints by avoiding usage of a BaseAddress, and using the client to pass HttpRequestMessages using SendAsync. I haven't been able to figure out cookies with this method yet. To avoid having the HttpClient store the cookies, I set UseCookies to false in the HttpClientHandler, and tried managing cookies via headers in the HttpRequest/ResponseMessages themselves, but it looks like HttpClient simply strips cookies when UseCookies is set to false, so I was unable to pass cookies between request. edit: cookies work fine because they are stored per domain.
Store several hundred different HttpClient instances in some sort of dictionary, and pull the appropriate one for each Uri as the requests come in. I'm not sure about the memory overhead on this though. Also each unique Uri is only verified once every 5 minutes, so I'm not sure if having an HttpClient used once every 5 minutes keeps an unnecessary number of ports open.
Keep using HttpWebRequests. Maybe this older method still performs better in this situation.
If anyone has faced a similar issue, I'd love some input on where to proceed on this.
Thanks!

The problem with creating new HttpClients for each request is that HttpClientHandler will close the underlying TCP/IP connection. However, if you are using each HttpClient for the 3 requests to one host and then hitting a different host, then keeping the connection open doesn't help when you move to a new host. So, you probably will not see perf problem with one client per host. HttpClient itself is a very lightweight object. It isn't going to cost much to create one.
However, HttpClient simply delegates the real work to HttpClientHandler which uses HttpWebRequest under the covers, therefore will be unlikely to have any better performance than directly using HttpWebRequest.
If you are looking for better performance, then I suggest looking into replacing HttpClientHandler with the new WinHttpHandler which bypasses HttpWebRequest and goes directly to the Win32 API to make calls.
The full source is available for WinHttpHandler on GitHub so you can see exactly how it handles cookies and credentials.
And I would be really interested to hear if you do get much better perf with WinHttpHandler.

To start with, what part of this would you need modified to suit your needs?
var urisToCheck = new List<Uri>(); //get these somehow
//basic auth work?
var credentials = new NetworkCredential("user", "pass");
var handler = new HttpClientHandler { Credentials = credentials };
var client = new HttpClient(handler);
Parallel.ForEach(urisToCheck,
async uri =>
{
var response = await client.GetAsync(uri.AbsoluteUri);
//check for whatever you want here
}
);

here's my basic API client that uses the same HttpClient object for every request.
using System;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;
//You need to install package Newtonsoft.Json > https://www.nuget.org/packages/Newtonsoft.Json/
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;
public class MyApiClient : IDisposable
{
private readonly TimeSpan _timeout;
private HttpClient _httpClient;
private HttpClientHandler _httpClientHandler;
private readonly string _baseUrl;
private const string ClientUserAgent = "my-api-client-v1";
private const string MediaTypeJson = "application/json";
public MyApiClient(string baseUrl, TimeSpan? timeout = null)
{
_baseUrl = NormalizeBaseUrl(baseUrl);
_timeout = timeout ?? TimeSpan.FromSeconds(90);
}
public async Task<string> PostAsync(string url, object input)
{
EnsureHttpClientCreated();
using (var requestContent = new StringContent(ConvertToJsonString(input), Encoding.UTF8, MediaTypeJson))
{
using (var response = await _httpClient.PostAsync(url, requestContent))
{
response.EnsureSuccessStatusCode();
return await response.Content.ReadAsStringAsync();
}
}
}
public async Task<TResult> PostAsync<TResult>(string url, object input) where TResult : class, new()
{
var strResponse = await PostAsync(url, input);
return JsonConvert.DeserializeObject<TResult>(strResponse, new JsonSerializerSettings
{
ContractResolver = new CamelCasePropertyNamesContractResolver()
});
}
public async Task<TResult> GetAsync<TResult>(string url) where TResult : class, new()
{
var strResponse = await GetAsync(url);
return JsonConvert.DeserializeObject<TResult>(strResponse, new JsonSerializerSettings
{
ContractResolver = new CamelCasePropertyNamesContractResolver()
});
}
public async Task<string> GetAsync(string url)
{
EnsureHttpClientCreated();
using (var response = await _httpClient.GetAsync(url))
{
response.EnsureSuccessStatusCode();
return await response.Content.ReadAsStringAsync();
}
}
public async Task<string> PutAsync(string url, object input)
{
return await PutAsync(url, new StringContent(JsonConvert.SerializeObject(input), Encoding.UTF8, MediaTypeJson));
}
public async Task<string> PutAsync(string url, HttpContent content)
{
EnsureHttpClientCreated();
using (var response = await _httpClient.PutAsync(url, content))
{
response.EnsureSuccessStatusCode();
return await response.Content.ReadAsStringAsync();
}
}
public async Task<string> DeleteAsync(string url)
{
EnsureHttpClientCreated();
using (var response = await _httpClient.DeleteAsync(url))
{
response.EnsureSuccessStatusCode();
return await response.Content.ReadAsStringAsync();
}
}
public void Dispose()
{
_httpClientHandler?.Dispose();
_httpClient?.Dispose();
}
private void CreateHttpClient()
{
_httpClientHandler = new HttpClientHandler
{
AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip
};
_httpClient = new HttpClient(_httpClientHandler, false)
{
Timeout = _timeout
};
_httpClient.DefaultRequestHeaders.UserAgent.ParseAdd(ClientUserAgent);
if (!string.IsNullOrWhiteSpace(_baseUrl))
{
_httpClient.BaseAddress = new Uri(_baseUrl);
}
_httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(MediaTypeJson));
}
private void EnsureHttpClientCreated()
{
if (_httpClient == null)
{
CreateHttpClient();
}
}
private static string ConvertToJsonString(object obj)
{
if (obj == null)
{
return string.Empty;
}
return JsonConvert.SerializeObject(obj, new JsonSerializerSettings
{
ContractResolver = new CamelCasePropertyNamesContractResolver()
});
}
private static string NormalizeBaseUrl(string url)
{
return url.EndsWith("/") ? url : url + "/";
}
}
Usage
using ( var client = new MyApiClient("http://localhost:8080"))
{
var response = client.GetAsync("api/users/findByUsername?username=alper").Result;
var userResponse = client.GetAsync<MyUser>("api/users/findByUsername?username=alper").Result;
}
Register this object as singleton to your dependency injection library. It's safe to reuse because it's stateless.
Do NOT recreate HTTPClient for each request.
Reuse Httpclient as much as possible

Adding headers when using httpClient.GetAsync

I'm implementing an API made by other colleagues with Apiary.io, in a Windows Store app project.
They show this example of a method I have to implement:
var baseAddress = new Uri("https://private-a8014-xxxxxx.apiary-mock.com/");
using (var httpClient = new HttpClient{ BaseAddress = baseAddress })
{
using (var response = await httpClient.GetAsync("user/list{?organizationId}"))
{
string responseData = await response.Content.ReadAsStringAsync();
}
}
In this and some other methods, I need to have a header with a token that I get before.
Here's an image of Postman (chrome extension) with the header I'm talking about:
How do I add that Authorization header to the request?

A later answer, but because no one gave this solution...
If you do not want to set the header on the HttpClient instance by adding it to the DefaultRequestHeaders, you could set headers per request.
But you will be obliged to use the SendAsync() method.
This is the right solution if you want to reuse the HttpClient -- which is a good practice for
performance and port exhaustion problems
doing something thread-safe
not sending the same headers every time
Use it like this:
using (var requestMessage =
new HttpRequestMessage(HttpMethod.Get, "https://your.site.com"))
{
requestMessage.Headers.Authorization =
new AuthenticationHeaderValue("Bearer", your_token);
await httpClient.SendAsync(requestMessage);
}

When using GetAsync with the HttpClient you can add the authorization headers like so:
httpClient.DefaultRequestHeaders.Authorization
= new AuthenticationHeaderValue("Bearer", "Your Oauth token");
This does add the authorization header for the lifetime of the HttpClient so is useful if you are hitting one site where the authorization header doesn't change.
Here is an detailed SO answer

The accepted answer works but can get complicated when you want to try adding Accept headers. This is what I ended up with. It seems simpler to me, so I think I'll stick with it in the future:
client.DefaultRequestHeaders.Add("Accept", "application/*+xml;version=5.1");
client.DefaultRequestHeaders.Add("Authorization", "Basic " + authstring);

Sometimes, you only need this code.
httpClient.DefaultRequestHeaders.Add("token", token);

Following the greenhoorn's answer, you can use "Extensions" like this:
public static class HttpClientExtensions
{
public static HttpClient AddTokenToHeader(this HttpClient cl, string token)
{
//int timeoutSec = 90;
//cl.Timeout = new TimeSpan(0, 0, timeoutSec);
string contentType = "application/json";
cl.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue(contentType));
cl.DefaultRequestHeaders.Add("Authorization", String.Format("Bearer {0}", token));
var userAgent = "d-fens HttpClient";
cl.DefaultRequestHeaders.Add("User-Agent", userAgent);
return cl;
}
}
And use:
string _tokenUpdated = "TOKEN";
HttpClient _client;
_client.AddTokenToHeader(_tokenUpdated).GetAsync("/api/values")

These days, if you are using MS Dependency Injection, it's highly recomended to plug in the IHttpClientFactory:
builder.Services.AddHttpClient("GitHub", httpClient =>
{
httpClient.BaseAddress = new Uri("https://api.github.com/");
// using Microsoft.Net.Http.Headers;
// The GitHub API requires two headers.
httpClient.DefaultRequestHeaders.Add(
HeaderNames.Accept, "application/vnd.github.v3+json");
httpClient.DefaultRequestHeaders.Add(
HeaderNames.UserAgent, "HttpRequestsSample");
});
var httpClient = _httpClientFactory.CreateClient("GitHub");
This way you avoid adding default request headers to a globally shared httpclient and moreover don't have to deal with manual creation of the HttpRequestMessage.
Source:
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/http-requests?view=aspnetcore-6.0#consumption-patterns