From d137a764d050e3d5296da2830a32f6d83bdb364f Mon Sep 17 00:00:00 2001
From: nsfisis <nsfisis@gmail.com>
Date: Mon, 9 Oct 2023 00:19:42 +0900
Subject: support path-based proxy

---
 conf.example.hcl | 21 +++++++++++++++++++++
 config.go        | 17 ++++++++++++++++-
 server.go        | 16 +++++++++++++++-
 3 files changed, 52 insertions(+), 2 deletions(-)

diff --git a/conf.example.hcl b/conf.example.hcl
index 8f1a56c..dfe18f8 100644
--- a/conf.example.hcl
+++ b/conf.example.hcl
@@ -11,4 +11,25 @@ server http {
             port = 8001
         }
     }
+
+    proxy b {
+        from {
+            path = "/b/"
+        }
+        to {
+            host = "127.0.0.1"
+            port = 8002
+        }
+    }
+
+    proxy c {
+        from {
+            host = "c.localhost"
+            path = "/c/"
+        }
+        to {
+            host = "127.0.0.1"
+            port = 8003
+        }
+    }
 }
diff --git a/config.go b/config.go
index ed4b3e0..6ad988f 100644
--- a/config.go
+++ b/config.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"net/netip"
 	"net/url"
+	"strings"
 
 	"github.com/hashicorp/hcl/v2/hclsimple"
 )
@@ -36,6 +37,7 @@ type ProxyConfig struct {
 
 type ProxyFromConfig struct {
 	Host string
+	Path string
 }
 
 type ProxyToConfig struct {
@@ -70,7 +72,8 @@ type InternalHCLProxyConfig struct {
 }
 
 type InternalHCLProxyFromConfig struct {
-	Host string `hcl:"host"`
+	Host string `hcl:"host,optional"`
+	Path string `hcl:"path,optional"`
 }
 
 type InternalHCLProxyToConfig struct {
@@ -93,6 +96,7 @@ func fromHCLConfigToConfig(hclConfig *InternalHCLConfig) *Config {
 				Name: p.Name,
 				From: ProxyFromConfig{
 					Host: p.From.Host,
+					Path: p.From.Path,
 				},
 				To: ProxyToConfig{
 					Host: p.To.Host,
@@ -180,6 +184,17 @@ func LoadConfig(fileName string) (*Config, error) {
 		}
 
 		for _, p := range server.Proxies {
+			if p.From.Path != "" {
+				if !strings.HasPrefix(p.From.Path, "/") {
+					return nil, fmt.Errorf("Path must start with '/'")
+				}
+				if !strings.HasSuffix(p.From.Path, "/") {
+					return nil, fmt.Errorf("Path must end with '/'")
+				}
+			}
+			if p.From.Host == "" && p.From.Path == "" {
+				return nil, fmt.Errorf("Either host or path must be specified")
+			}
 			_, err := url.Parse(fmt.Sprintf("http://%s:%d", p.To.Host, p.To.Port))
 			if err != nil {
 				return nil, fmt.Errorf("Invalid host or port: %s:%d", p.To.Host, p.To.Port)
diff --git a/server.go b/server.go
index 47c52dd..830a6e4 100644
--- a/server.go
+++ b/server.go
@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"net/http/httputil"
 	"net/url"
+	"strings"
 )
 
 type multipleReverseProxyServer struct {
@@ -16,10 +17,22 @@ type multipleReverseProxyServer struct {
 
 type rewriteRule struct {
 	fromHost string
+	fromPath string
 	toUrl    *url.URL
 	proxy    *httputil.ReverseProxy
 }
 
+func (r *rewriteRule) matches(host, path string) bool {
+	ret := true
+	if r.fromHost != "" {
+		ret = ret && r.fromHost == host
+	}
+	if r.fromPath != "" {
+		ret = ret && strings.HasPrefix(path+"/", r.fromPath)
+	}
+	return ret
+}
+
 func newMultipleReverseProxyServer(ps []ProxyConfig) *multipleReverseProxyServer {
 	var rules []rewriteRule
 	for _, p := range ps {
@@ -30,6 +43,7 @@ func newMultipleReverseProxyServer(ps []ProxyConfig) *multipleReverseProxyServer
 		}
 		rules = append(rules, rewriteRule{
 			fromHost: p.From.Host,
+			fromPath: p.From.Path,
 			toUrl:    targetUrl,
 			proxy: &httputil.ReverseProxy{
 				Rewrite: func(r *httputil.ProxyRequest) {
@@ -50,7 +64,7 @@ func (s *multipleReverseProxyServer) tryServeHTTP(
 	hostWithoutPort string,
 ) bool {
 	for _, rule := range s.rules {
-		if rule.fromHost == hostWithoutPort {
+		if rule.matches(hostWithoutPort, r.URL.Path) {
 			rule.proxy.ServeHTTP(w, r)
 			return true
 		}
-- 
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