From 075b9113bc6a0cfbd933b678c18d5345b18f44e1 Mon Sep 17 00:00:00 2001
From: Marco Kittel <marco@kittel.dev>
Date: Sat, 28 Jun 2025 09:50:35 +0200
Subject: [PATCH] Reverse Proxy Beispiel

---
 README.md          | 11 +++++++++++
 cmd/shell/main.go  | 24 ++++++++++++++++++++++++
 cmd/websrv/main.go | 16 ++++++++++++++++
 go.mod             |  3 +++
 proxy/proxy.go     | 44 ++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 98 insertions(+)
 create mode 100644 cmd/shell/main.go
 create mode 100644 cmd/websrv/main.go
 create mode 100644 go.mod
 create mode 100644 proxy/proxy.go

diff --git a/README.md b/README.md
index e69de29..96f6959 100644
--- a/README.md
+++ b/README.md
@@ -0,0 +1,11 @@
+#
+Zum Test Proxy und zwei Webserver auf Port 8081 und 8082 aufrufen.
+## Proxy aufrufen
+go run cmd/shell/main.go 
+## Webserver aufrufen
+go run cmd/websrv/main.go 8081
+go run cmd/websrv/main.go 8082
+
+
+
+
diff --git a/cmd/shell/main.go b/cmd/shell/main.go
new file mode 100644
index 0000000..36fc669
--- /dev/null
+++ b/cmd/shell/main.go
@@ -0,0 +1,24 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+
+	"gittea.kittel.dev/marco/proxy/proxy"
+)
+
+var (
+	PORT = 8080
+)
+
+func main() {
+	targets := []string{
+		"http://localhost:8081",
+		"http://localhost:8082",
+	}
+	p := proxy.NewProxy(targets)
+	log.Println("Reverse proxy started on %d", PORT)
+	portStr := fmt.Sprintf(":%d", PORT)
+	log.Fatal(http.ListenAndServe(portStr, p))
+}
diff --git a/cmd/websrv/main.go b/cmd/websrv/main.go
new file mode 100644
index 0000000..2ff3640
--- /dev/null
+++ b/cmd/websrv/main.go
@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+)
+
+func main() {
+	port := os.Args[1]
+	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, "Hello from backend %s", port)
+	})
+	fmt.Println("Backend listening on port:", port)
+	http.ListenAndServe(":"+port, nil)
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..e3c6030
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module gittea.kittel.dev/marco/proxy
+
+go 1.24.4
diff --git a/proxy/proxy.go b/proxy/proxy.go
new file mode 100644
index 0000000..d82a9f4
--- /dev/null
+++ b/proxy/proxy.go
@@ -0,0 +1,44 @@
+package proxy
+
+import (
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"sync/atomic"
+)
+
+type Proxy struct {
+	targets []*url.URL
+	counter uint64
+}
+
+func NewProxy(targets []string) *Proxy {
+	parsed := []*url.URL{}
+	for _, t := range targets {
+		u, err := url.Parse(t)
+		if err != nil {
+			log.Fatalf("")
+		}
+		parsed = append(parsed, u)
+	}
+	return &Proxy{targets: parsed}
+}
+
+func (p *Proxy) getNextTarget() *url.URL {
+	i := atomic.AddUint64(&p.counter, 1)
+	return p.targets[(int(i)-1)%len(p.targets)]
+}
+
+func (p *Proxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	target := p.getNextTarget()
+	proxy := httputil.NewSingleHostReverseProxy(target)
+	r.Host = target.Host
+	log.Printf("Weiterleitung der Anfrage %s %s --> %s", r.Method, r.URL.Path, target)
+	proxy.ErrorHandler = func(w http.ResponseWriter, r *http.Request, err error) {
+		log.Printf("!! Proxy error for %s: %v", r.URL.Path, err)
+		http.Error(w, "Reverse Proxy Error", http.StatusBadGateway)
+	}
+
+	proxy.ServeHTTP(w, r)
+}