From 39c0c5cb45c76c101c757e21b80491790469ee7e Mon Sep 17 00:00:00 2001
From: Axetroy <axetroy.dev@gmail.com>
Date: Sat, 8 Jan 2022 02:13:28 +0800
Subject: [PATCH] feat: support cusom proxy

---
 README.md       | 11 +++++++++++
 README_en-US.md | 11 +++++++++++
 proxy.go        | 25 ++++++++++++++++++++++---
 3 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/README.md b/README.md
index 92200a0..91230dc 100644
--- a/README.md
+++ b/README.md
@@ -82,6 +82,17 @@ openssl req -new -x509 -sha256 -key server.key -out server.pem -days 3650
 forward --tls-cert-file=server.pem --tls-key-file=server.key http://example.com
 ```
 
+2. 自定义代理请求
+
+```bash
+# 代理 https://github.com
+forward https://github.com
+# 发起请求
+curl http://0.0.0.0:80/api # 实际请求 https://github.com/api
+# 发起自定义代理
+curl -H "X-Proxy-Target: https://www.google.com" http://0.0.0.0/api # 实际请求 https://www.google.com/api
+```
+
 ### 开源许可
 
 The [MIT License](LICENSE)
diff --git a/README_en-US.md b/README_en-US.md
index bdd715c..c97129d 100644
--- a/README_en-US.md
+++ b/README_en-US.md
@@ -82,6 +82,17 @@ openssl req -new -x509 -sha256 -key server.key -out server.pem -days 3650
 forward --tls-cert-file=server.pem --tls-key-file=server.key http://example.com
 ```
 
+2. Custom proxy
+
+```bash
+# proxy https://github.com
+forward https://github.com
+# send request
+curl http://0.0.0.0:80/api # request https://github.com/api
+# send custom request
+curl -H "X-Proxy-Target: https://www.google.com" http://0.0.0.0/api # request https://www.google.com/api
+```
+
 ### License
 
 The [MIT License](LICENSE)
diff --git a/proxy.go b/proxy.go
index 86db4f0..63b1b80 100644
--- a/proxy.go
+++ b/proxy.go
@@ -27,6 +27,12 @@ var (
 	regIntegrity = regexp.MustCompile(`\sintegrity="[^"]+"`)
 )
 
+const (
+	headerXProxyTarget = "X-Proxy-Target"
+	headerXOriginHost  = "X-Origin-Host"
+	headerXProxyClient = "X-Proxy-Client"
+)
+
 type ProxyServer struct {
 	*ProxyServerOptions
 	proxy *httputil.ReverseProxy
@@ -149,9 +155,22 @@ func (p *ProxyServer) modifyRequest(req *http.Request) {
 				target = *u
 			}
 		}
+	} else if req.Header.Get(headerXProxyTarget) != "" {
+		targetUrl := req.Header.Get(headerXProxyTarget)
+
+		if u, err := url.Parse(targetUrl); err == nil {
+			if u.Scheme == "" {
+				if p.UseSSL {
+					u.Scheme = "https"
+				} else {
+					u.Scheme = "http"
+				}
+			}
+			target = *u
+		}
 	}
 
-	req.Header.Set("X-Origin-Host", req.Host)
+	req.Header.Set(headerXOriginHost, req.Host)
 	req.Host = target.Host
 	if isProxyUrl {
 		req.URL = &target
@@ -205,7 +224,7 @@ func (p *ProxyServer) modifyResponse(res *http.Response) error {
 		}
 	}
 
-	proxyHost := res.Request.Header.Get("X-Origin-Host") // localhost:8080 or localhost
+	proxyHost := res.Request.Header.Get(headerXOriginHost) // localhost:8080 or localhost
 
 	var hostName string
 
@@ -221,7 +240,7 @@ func (p *ProxyServer) modifyResponse(res *http.Response) error {
 		hostName = proxyHost
 	}
 
-	res.Header.Set("X-Proxy-Client", "Forward-Cli")
+	res.Header.Set(headerXProxyClient, "Forward-Cli")
 	res.Header.Del("Expect-CT")
 
 	// disable cache