I've already answered this question [in another thread][1].
```CSharp //Usage: var handler = new RedirectHandler(new HttpClientHandler()); var client = new HttpClient(handler);
//redirects to HTTPS var url = "http://stackoverflow.com/";
//AutoRedirect is true var response = await HttpClientHelper.SendAsync(client, url, autoRedirect: true).ConfigureAwait(false); //AutoRedirect is false response = await HttpClientHelper.SendAsync(client, url, autoRedirect: false).ConfigureAwait(false);
public static class HttpClientHelper { private const string AutoRedirectPropertyKey = "RequestAutoRedirect"; private static readonly HttpRequestOptionsKey<bool?> AutoRedirectOptionsKey = new(AutoRedirectPropertyKey);
public static Task<HttpResponseMessage> SendAsync(HttpClient client, string url, bool autoRedirect = true) { var uri = new Uri(url); var request = new HttpRequestMessage { RequestUri = uri, Method = HttpMethod.Get }; request.SetAutoRedirect(autoRedirect);
return client.SendAsync(request); }
public static void SetAutoRedirect(this HttpRequestMessage request, bool autoRedirect) { request.Options.Set(AutoRedirectOptionsKey, autoRedirect); } public static bool? GetAutoRedirect(this HttpRequestMessage request) { request.Options.TryGetValue(AutoRedirectOptionsKey, out var value); return value; }
public static HttpMessageHandler? GetMostInnerHandler(this HttpMessageHandler? self) { while (self is DelegatingHandler handler) { self = handler.InnerHandler; }
return self; } }
public class RedirectHandler : DelegatingHandler { private int MaxAutomaticRedirections { get; set; } private bool InitialAutoRedirect { get; set; }
public RedirectHandler(HttpMessageHandler innerHandler) : base(innerHandler) { var mostInnerHandler = innerHandler.GetMostInnerHandler(); SetupCustomAutoRedirect(mostInnerHandler); }
private void SetupCustomAutoRedirect(HttpMessageHandler? mostInnerHandler) { //Store the initial auto-redirect & max-auto-redirect values. //Disabling auto-redirect and handle redirects manually. try { switch (mostInnerHandler) { case HttpClientHandler hch: InitialAutoRedirect = hch.AllowAutoRedirect; MaxAutomaticRedirections = hch.MaxAutomaticRedirections; hch.AllowAutoRedirect = false; break; case SocketsHttpHandler shh: InitialAutoRedirect = shh.AllowAutoRedirect; MaxAutomaticRedirections = shh.MaxAutomaticRedirections; shh.AllowAutoRedirect = false; break; default: Debug.WriteLine("[SetupCustomAutoRedirect] Unknown handler type: {0}", mostInnerHandler?.GetType().FullName); InitialAutoRedirect = true; MaxAutomaticRedirections = 17; break; } } catch (Exception e) { Debug.WriteLine(e.Message); InitialAutoRedirect = true; MaxAutomaticRedirections = 17; } }
private bool IsRedirectAllowed(HttpRequestMessage request) { var value = request.GetAutoRedirect(); if (value == null) return InitialAutoRedirect; return value == true; } protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { var redirectCount = 0; var response = await base.SendAsync(request, cancellationToken).ConfigureAwait(false);
//Manual Redirect //https://github.com/dotnet/runtime/blob/ccfe21882e4a2206ce49cd5b32d3eb3cab3e530f/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/RedirectHandler.cs Uri? redirectUri; while (IsRedirect(response) && IsRedirectAllowed(request) && (redirectUri = GetUriForRedirect(request.RequestUri!, response)) != null) { redirectCount++; if (redirectCount > MaxAutomaticRedirections) break;
response.Dispose();
// Clear the authorization header. request.Headers.Authorization = null; // Set up for the redirect request.RequestUri = redirectUri;
if (RequestRequiresForceGet(response.StatusCode, request.Method)) { request.Method = HttpMethod.Get; request.Content = null; if (request.Headers.TransferEncodingChunked == true) request.Headers.TransferEncodingChunked = false; }
// Issue the redirected request. response = await base.SendAsync(request, cancellationToken).ConfigureAwait(false); }
return response; } private bool IsRedirect(HttpResponseMessage response) { switch (response.StatusCode) { case HttpStatusCode.MultipleChoices: case HttpStatusCode.Moved: case HttpStatusCode.Found: case HttpStatusCode.SeeOther: case HttpStatusCode.TemporaryRedirect: case HttpStatusCode.PermanentRedirect: return true;
default: return false; } } private static Uri? GetUriForRedirect(Uri requestUri, HttpResponseMessage response) { var location = response.Headers.Location; if (location == null) { return null; }
// Ensure the redirect location is an absolute URI. if (!location.IsAbsoluteUri) { location = new Uri(requestUri, location); }
// Per https://tools.ietf.org/html/rfc7231#section-7.1.2, a redirect location without a // fragment should inherit the fragment from the original URI. var requestFragment = requestUri.Fragment; if (!string.IsNullOrEmpty(requestFragment)) { var redirectFragment = location.Fragment; if (string.IsNullOrEmpty(redirectFragment)) { location = new UriBuilder(location) { Fragment = requestFragment }.Uri; } }
return location; } private static bool RequestRequiresForceGet(HttpStatusCode statusCode, HttpMethod requestMethod) { switch (statusCode) { case HttpStatusCode.Moved: case HttpStatusCode.Found: case HttpStatusCode.MultipleChoices: return requestMethod == HttpMethod.Post; case HttpStatusCode.SeeOther: return requestMethod != HttpMethod.Get && requestMethod != HttpMethod.Head; default: return false; } } } ```
The main idea is to disable automatic redirects and handle them manually using a custom **RedirectHandler**.
1. Before sending a request, we utilize the extension method **SetAutoRedirect** to store the redirect rule in the request's options dictionary. 2. Upon receiving a response, we check if it is a redirect. If it is, we then examine the request's options dictionary for a redirect rule using the extension method **GetAutoRedirect**. 3. Repeat #2 until **MaxAutomaticRedirections** is reached or there are no further redirects.

[1]: https://stackoverflow.com/a/76392591/3230716

3 years later, here is my implementation:
```CSharp //Usage: var handler = new RedirectHandler(new HttpClientHandler()); var client = new HttpClient(handler);
//redirects to HTTPS var url = "http://stackoverflow.com/";
//AutoRedirect is true var response = await HttpClientHelper.SendAsync(client, url, autoRedirect: true).ConfigureAwait(false); //AutoRedirect is false response = await HttpClientHelper.SendAsync(client, url, autoRedirect: false).ConfigureAwait(false);
public static class HttpClientHelper { private const string AutoRedirectPropertyKey = "RequestAutoRedirect"; private static readonly HttpRequestOptionsKey<bool?> AutoRedirectOptionsKey = new(AutoRedirectPropertyKey);
public static Task<HttpResponseMessage> SendAsync(HttpClient client, string url, bool autoRedirect = true) { var uri = new Uri(url); var request = new HttpRequestMessage { RequestUri = uri, Method = HttpMethod.Get }; request.SetAutoRedirect(autoRedirect);
return client.SendAsync(request); }
public static void SetAutoRedirect(this HttpRequestMessage request, bool autoRedirect) { request.Options.Set(AutoRedirectOptionsKey, autoRedirect); } public static bool? GetAutoRedirect(this HttpRequestMessage request) { request.Options.TryGetValue(AutoRedirectOptionsKey, out var value); return value; }
public static HttpMessageHandler? GetMostInnerHandler(this HttpMessageHandler? self) { while (self is DelegatingHandler handler) { self = handler.InnerHandler; }
return self; } }
public class RedirectHandler : DelegatingHandler { private int MaxAutomaticRedirections { get; set; } private bool InitialAutoRedirect { get; set; }
public RedirectHandler(HttpMessageHandler innerHandler) : base(innerHandler) { var mostInnerHandler = innerHandler.GetMostInnerHandler(); SetupCustomAutoRedirect(mostInnerHandler); }
private void SetupCustomAutoRedirect(HttpMessageHandler? mostInnerHandler) { //Store the initial auto-redirect & max-auto-redirect values. //Disabling auto-redirect and handle redirects manually. try { switch (mostInnerHandler) { case HttpClientHandler hch: InitialAutoRedirect = hch.AllowAutoRedirect; MaxAutomaticRedirections = hch.MaxAutomaticRedirections; hch.AllowAutoRedirect = false; break; case SocketsHttpHandler shh: InitialAutoRedirect = shh.AllowAutoRedirect; MaxAutomaticRedirections = shh.MaxAutomaticRedirections; shh.AllowAutoRedirect = false; break; default: Debug.WriteLine("[SetupCustomAutoRedirect] Unknown handler type: {0}", mostInnerHandler?.GetType().FullName); InitialAutoRedirect = true; MaxAutomaticRedirections = 17; break; } } catch (Exception e) { Debug.WriteLine(e.Message); InitialAutoRedirect = true; MaxAutomaticRedirections = 17; } }
private bool IsRedirectAllowed(HttpRequestMessage request) { var value = request.GetAutoRedirect(); if (value == null) return InitialAutoRedirect; return value == true; } protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) { var redirectCount = 0; var response = await base.SendAsync(request, cancellationToken).ConfigureAwait(false);
//Manual Redirect //https://github.com/dotnet/runtime/blob/ccfe21882e4a2206ce49cd5b32d3eb3cab3e530f/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/RedirectHandler.cs Uri? redirectUri; while (IsRedirect(response) && IsRedirectAllowed(request) && (redirectUri = GetUriForRedirect(request.RequestUri!, response)) != null) { redirectCount++; if (redirectCount > MaxAutomaticRedirections) break;
response.Dispose();
// Clear the authorization header. request.Headers.Authorization = null; // Set up for the redirect request.RequestUri = redirectUri;
if (RequestRequiresForceGet(response.StatusCode, request.Method)) { request.Method = HttpMethod.Get; request.Content = null; if (request.Headers.TransferEncodingChunked == true) request.Headers.TransferEncodingChunked = false; }
// Issue the redirected request. response = await base.SendAsync(request, cancellationToken).ConfigureAwait(false); }
return response; } private bool IsRedirect(HttpResponseMessage response) { switch (response.StatusCode) { case HttpStatusCode.MultipleChoices: case HttpStatusCode.Moved: case HttpStatusCode.Found: case HttpStatusCode.SeeOther: case HttpStatusCode.TemporaryRedirect: case HttpStatusCode.PermanentRedirect: return true;
default: return false; } } private static Uri? GetUriForRedirect(Uri requestUri, HttpResponseMessage response) { var location = response.Headers.Location; if (location == null) { return null; }
// Ensure the redirect location is an absolute URI. if (!location.IsAbsoluteUri) { location = new Uri(requestUri, location); }
// Per https://tools.ietf.org/html/rfc7231#section-7.1.2, a redirect location without a // fragment should inherit the fragment from the original URI. var requestFragment = requestUri.Fragment; if (!string.IsNullOrEmpty(requestFragment)) { var redirectFragment = location.Fragment; if (string.IsNullOrEmpty(redirectFragment)) { location = new UriBuilder(location) { Fragment = requestFragment }.Uri; } }
return location; } private static bool RequestRequiresForceGet(HttpStatusCode statusCode, HttpMethod requestMethod) { switch (statusCode) { case HttpStatusCode.Moved: case HttpStatusCode.Found: case HttpStatusCode.MultipleChoices: return requestMethod == HttpMethod.Post; case HttpStatusCode.SeeOther: return requestMethod != HttpMethod.Get && requestMethod != HttpMethod.Head; default: return false; } } } ```
The main idea is to disable automatic redirects and handle them manually using a custom **RedirectHandler**.
1. Before sending a request, we utilize the extension method **SetAutoRedirect** to store the redirect rule in the request's options dictionary. 2. Upon receiving a response, we check if it is a redirect. If it is, we then examine the request's options dictionary for a redirect rule using the extension method **GetAutoRedirect**. 3. Repeat #2 until **MaxAutomaticRedirections** is reached or there are no further redirects.