反向代理可以在中间件中模拟/实现：
首先是启动类，我们在其中添加 IUrlRewriter 服务和 ProxyMiddleware。
public class Startup
{
private readonly IConfiguration _configuration;
public Startup(IConfiguration configuration)
{
_configuration = configuration;
}
public void ConfigureServices(IServiceCollection services)
{
services.AddSingleton<IUrlRewriter>(new SingleRegexRewriter(@"^/POC/(.*)", "http://192.168.7.73:3001/$1"));
}
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseRewriter(new RewriteOptions().AddRedirectToHttps());
app.UseMiddleware<ProxyMiddleware>();
}
}
接下来我们将创建 IUrlRewriter 的基本实现。 RewriteUri 方法必须将 HttpContext 转换为绝对 Uri。如果 url 不应在中间件中重定向，则返回 null。
public interface IUrlRewriter
{
Task<Uri> RewriteUri(HttpContext context);
}
public class SingleRegexRewriter : IUrlRewriter
{
private readonly string _pattern;
private readonly string _replacement;
private readonly RegexOptions _options;
public SingleRegexRewriter(string pattern, string replacement)
: this(pattern, replacement, RegexOptions.None) { }
public SingleRegexRewriter(string pattern, string replacement, RegexOptions options)
{
_pattern = pattern ?? throw new ArgumentNullException(nameof(pattern));
_replacement = replacement ?? throw new ArgumentNullException(nameof(pattern));
_options = options;
}
public Task<Uri> RewriteUri(HttpContext context)
{
string url = context.Request.Path + context.Request.QueryString;
var newUri = Regex.Replace(url, _pattern, _replacement);
if (Uri.TryCreate(newUri, UriKind.Absolute, out var targetUri))
{
return Task.FromResult(targetUri);
}
return Task.FromResult((Uri)null);
}
}
然后是中间件（从旧版本的 asp net proxy 中窃取）repo https://github.com/aspnet/Proxy/）并定制。它获取 IUrlRewrite 服务作为参数Invoke method.
管道是：
- 尝试重写网址
- 创建 HttpRequest 消息
- 复制请求头和内容
- 发送请求
- 复制响应头
- 复制回复内容
- done
Et voila
public class ProxyMiddleware
{
private static readonly HttpClient _httpClient = new HttpClient(new HttpClientHandler()
{
AllowAutoRedirect = false,
MaxConnectionsPerServer = int.MaxValue,
UseCookies = false,
});
private const string CDN_HEADER_NAME = "Cache-Control";
private static readonly string[] NotForwardedHttpHeaders = new[] { "Connection", "Host" };
private readonly RequestDelegate _next;
private readonly ILogger<ProxyMiddleware> _logger;
public ProxyMiddleware(
RequestDelegate next,
ILogger<ProxyMiddleware> logger)
{
_next = next;
_logger = logger;
}
public async Task Invoke(HttpContext context, IUrlRewriter urlRewriter)
{
var targetUri = await urlRewriter.RewriteUri(context);
if (targetUri != null)
{
var requestMessage = GenerateProxifiedRequest(context, targetUri);
await SendAsync(context, requestMessage);
return;
}
await _next(context);
}
private async Task SendAsync(HttpContext context, HttpRequestMessage requestMessage)
{
using (var responseMessage = await _httpClient.SendAsync(requestMessage, HttpCompletionOption.ResponseHeadersRead, context.RequestAborted))
{
context.Response.StatusCode = (int)responseMessage.StatusCode;
foreach (var header in responseMessage.Headers)
{
context.Response.Headers[header.Key] = header.Value.ToArray();
}
foreach (var header in responseMessage.Content.Headers)
{
context.Response.Headers[header.Key] = header.Value.ToArray();
}
context.Response.Headers.Remove("transfer-encoding");
if (!context.Response.Headers.ContainsKey(CDN_HEADER_NAME))
{
context.Response.Headers.Add(CDN_HEADER_NAME, "no-cache, no-store");
}
await responseMessage.Content.CopyToAsync(context.Response.Body);
}
}
private static HttpRequestMessage GenerateProxifiedRequest(HttpContext context, Uri targetUri)
{
var requestMessage = new HttpRequestMessage();
CopyRequestContentAndHeaders(context, requestMessage);
requestMessage.RequestUri = targetUri;
requestMessage.Headers.Host = targetUri.Host;
requestMessage.Method = GetMethod(context.Request.Method);
return requestMessage;
}
private static void CopyRequestContentAndHeaders(HttpContext context, HttpRequestMessage requestMessage)
{
var requestMethod = context.Request.Method;
if (!HttpMethods.IsGet(requestMethod) &&
!HttpMethods.IsHead(requestMethod) &&
!HttpMethods.IsDelete(requestMethod) &&
!HttpMethods.IsTrace(requestMethod))
{
var streamContent = new StreamContent(context.Request.Body);
requestMessage.Content = streamContent;
}
foreach (var header in context.Request.Headers)
{
if (!NotForwardedHttpHeaders.Contains(header.Key))
{
if (header.Key != "User-Agent")
{
if (!requestMessage.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray()) && requestMessage.Content != null)
{
requestMessage.Content?.Headers.TryAddWithoutValidation(header.Key, header.Value.ToArray());
}
}
else
{
string userAgent = header.Value.Count > 0 ? (header.Value[0] + " " + context.TraceIdentifier) : string.Empty;
if (!requestMessage.Headers.TryAddWithoutValidation(header.Key, userAgent) && requestMessage.Content != null)
{
requestMessage.Content?.Headers.TryAddWithoutValidation(header.Key, userAgent);
}
}
}
}
}
private static HttpMethod GetMethod(string method)
{
if (HttpMethods.IsDelete(method)) return HttpMethod.Delete;
if (HttpMethods.IsGet(method)) return HttpMethod.Get;
if (HttpMethods.IsHead(method)) return HttpMethod.Head;
if (HttpMethods.IsOptions(method)) return HttpMethod.Options;
if (HttpMethods.IsPost(method)) return HttpMethod.Post;
if (HttpMethods.IsPut(method)) return HttpMethod.Put;
if (HttpMethods.IsTrace(method)) return HttpMethod.Trace;
return new HttpMethod(method);
}
}
奖励：其他一些重写器
public class PrefixRewriter : IUrlRewriter
{
private readonly PathString _prefix;
private readonly string _newHost;
public PrefixRewriter(PathString prefix, string newHost)
{
_prefix = prefix;
_newHost = newHost;
}
public Task<Uri> RewriteUri(HttpContext context)
{
if (context.Request.Path.StartsWithSegments(_prefix))
{
var newUri = context.Request.Path.Value.Remove(0, _prefix.Value.Length) + context.Request.QueryString;
var targetUri = new Uri(_newHost + newUri);
return Task.FromResult(targetUri);
}
return Task.FromResult((Uri)null);
}
}
public class MergeRewriter : IUrlRewriter
{
private readonly List<IUrlRewriter> _rewriters = new List<IUrlRewriter>();
public MergeRewriter()
{
}
public MergeRewriter(IEnumerable<IUrlRewriter> rewriters)
{
if (rewriters == null) throw new ArgumentNullException(nameof(rewriters));
_rewriters.AddRange(rewriters);
}
public MergeRewriter Add(IUrlRewriter rewriter)
{
if (rewriter == null) throw new ArgumentNullException(nameof(rewriter));
_rewriters.Add(rewriter);
return this;
}
public async Task<Uri> RewriteUri(HttpContext context)
{
foreach (var rewriter in _rewriters)
{
var targetUri = await rewriter.RewriteUri(context);
if(targetUri != null)
{
return targetUri;
}
}
return null;
}
}
// In Statup.cs
public void ConfigureServices(IServiceCollection services)
{
services.AddSingleton<IUrlRewriter>(new MergeRewriter()
.Add(new PrefixRewriter("/POC/API", "http://localhost:1234"))
.Add(new SingleRegexRewriter(@"^/POC/(.*)", "http://192.168.7.73:3001/$1")));
}
Edit
我发现一个项目可以做同样的事情，但有更多其他功能https://github.com/damianh/ProxyKit https://github.com/damianh/ProxyKit作为 nuget 包
