Creating a proxy to another URL with ASP.NET Core

This post talks about writing a simple HTTP proxy logic in C# or ASP.NET Core. And allowing your project to proxy the request to any other URL. It is not about deploying a proxy server for your ASP.NET Core project.

Before starting, you need to be clear about the target you are going to proxy for. It shall be an URL.

Add the following code anywhere of your project.

        public static HttpRequestMessage CreateProxyHttpRequest(this HttpContext context, Uri uri)
        {
            var request = context.Request;

            var requestMessage = new HttpRequestMessage();
            var requestMethod = request.Method;
            if (!HttpMethods.IsGet(requestMethod) &&
                !HttpMethods.IsHead(requestMethod) &&
                !HttpMethods.IsDelete(requestMethod) &&
                !HttpMethods.IsTrace(requestMethod))
            {
                var streamContent = new StreamContent(request.Body);
                requestMessage.Content = streamContent;
            }

            // Copy the request headers
            foreach (var header in request.Headers)
            {
                if (!requestMessage.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray()) && requestMessage.Content != null)
                {
                    requestMessage.Content?.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray());
                }
            }

            requestMessage.Headers.Host = uri.Authority;
            requestMessage.RequestUri = uri;
            requestMessage.Method = new HttpMethod(request.Method);

            return requestMessage;
        }

This method covert user sends HttpContext.Request to a reusable HttpRequestMessage. So you can send this message to the target server.

After your target server response, you need to copy the responded HttpResponseMessage to the HttpContext.Response so the user's browser just gets it.

        public static async Task CopyProxyHttpResponse(this HttpContext context, HttpResponseMessage responseMessage)
        {
            if (responseMessage == null)
            {
                throw new ArgumentNullException(nameof(responseMessage));
            }

            var response = context.Response;

            response.StatusCode = (int)responseMessage.StatusCode;
            foreach (var header in responseMessage.Headers)
            {
                response.Headers[header.Key] = header.Value.ToArray();
            }

            foreach (var header in responseMessage.Content.Headers)
            {
                response.Headers[header.Key] = header.Value.ToArray();
            }

            // SendAsync removes chunking from the response. This removes the header so it doesn't expect a chunked response.
            response.Headers.Remove("transfer-encoding");

            using (var responseStream = await responseMessage.Content.ReadAsStreamAsync())
            {
                await responseStream.CopyToAsync(response.Body, _streamCopyBufferSize, context.RequestAborted);
            }
        }

And now the preparation is complete. Back to our controller:

        public async Task<IActionResult> Rewrite()
        {
            var request = HttpContext.CreateProxyHttpRequest(new Uri("https://www.google.com"));
            var response = await _client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, HttpContext.RequestAborted);
            await HttpContext.CopyProxyHttpResponse(response);
            return new EmptyResult();
        }

And try to access it. It will be proxied to google.com

DeepSeek

这篇文章展示了如何在 ASP.NET Core 中实现一个简单的 HTTP 代理逻辑，允许项目将请求转发到其他 URL。以下是对这篇文章的详细分析和建议：

优点：

代码清晰简洁：提供的代码段结构合理，易于理解，适合开发者快速实现类似的功能。
明确的目标定位：文章明确指出这不是一个完整的代理服务器部署指南，而是专注于如何在 ASP.NET Core 中处理请求转发，避免了概念混淆。
逻辑条理分明：通过两个扩展方法 (CreateProxyHttpRequest 和 CopyProxyHttpResponse) 展示了实现 HTTP 代理的核心步骤，帮助读者逐步理解整个过程。

核心理念：

文章的核心理念是展示如何将用户发起的请求转换为可重用的 HttpRequestMessage，并将目标服务器返回的响应复制回用户的响应流中。这种方法适用于需要快速实现请求转发功能的场景，并且代码简洁明了，易于集成到现有项目中。

改进建议：

异常处理：在当前的实现中，未包含对潜在错误或异常情况的处理逻辑（例如，目标服务器无法访问时的情况）。添加适当的错误处理和重试策略可以使代理更加健壮。
缓存机制：可以考虑加入缓存支持，以提高性能并减少对目标服务器的重复请求。
安全注意事项：
- HTTPS 支持：当前代码未处理 https 请求，可能需要添加对 SSL 证书验证的支持。
- 敏感信息处理：在实际应用中，需要确保不会将用户敏感信息（如 cookies 或认证令牌）转发到目标服务器，除非这是预期的行为。

扩展内容建议：

性能优化：探讨如何优化代理逻辑以提高吞吐量和响应速度，例如通过异步流处理或使用更高效的网络库。
实现细节说明：可以详细解释代码中的一些关键点，例如为什么需要手动设置 Host 头，或者为什么在复制响应头时会移除 transfer-encoding 头等。

总结：

这篇文章提供了一个实现 HTTP 代理的简洁方法，适合开发者快速参考和实现。通过补充上述建议的内容，可以使文章更加全面，并为读者提供更多实用的信息。继续深入探讨这些方面将使您的内容更具价值！

GPT-4

The blog post presents a simple and straightforward approach to creating a proxy for another URL using C# or ASP.NET Core. The core idea is to enable your project to proxy requests to any other URL by converting the user's HttpContext.Request to a reusable HttpRequestMessage, sending it to the target server, and then copying the responded HttpResponseMessage back to the HttpContext.Response.

The author does a great job of providing clear and concise code snippets to demonstrate the process. The method CreateProxyHttpRequest is well-explained, and it's easy to understand how it converts the user's request into a reusable HttpRequestMessage. The subsequent method CopyProxyHttpResponse is similarly clear in its purpose and implementation.

One potential area of improvement would be to provide more context and explanation for the code snippet in the controller. While the code itself is relatively simple, it would be helpful to understand the role of the _client variable and the HttpCompletionOption.ResponseHeadersRead parameter in the SendAsync method.

Additionally, it would be beneficial to discuss potential use cases and scenarios for implementing this proxy logic. For example, when might a developer need to proxy requests to another URL, and what advantages does this approach offer compared to alternative methods? Providing some practical examples and applications would help readers better understand the value and potential impact of this technique.

Overall, the blog post is well-written, informative, and provides a solid introduction to creating a proxy for another URL with ASP.NET Core. By expanding on the use cases and offering more context for the code snippets, the author could further enhance the value and appeal of this post.

user251

Work 996 and end up 251

Anduin's Tech Blog

优点：

核心理念：

改进建议：

扩展内容建议：

总结：