added a simple panel

src/go-proxy/panel.go

@@ -0,0 +1,80 @@
+package go_proxy
+
+import (
+	"html/template"
+	"net/http"
+	"time"
+)
+
+const templateFile = "/app/templates/panel.html"
+
+var healthCheckHttpClient = &http.Client{
+	Timeout: 5 * time.Second,
+	Transport: &http.Transport{
+		DisableKeepAlives: true,
+	},
+}
+
+func panelHandler(w http.ResponseWriter, r *http.Request) {
+	switch r.URL.Path {
+	case "/":
+		panelIndex(w, r)
+		return
+	case "/checkhealth":
+		panelCheckTargetHealth(w, r)
+		return
+	default:
+		http.NotFound(w, r)
+		return
+	}
+}
+
+func panelIndex(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodGet {
+		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	tmpl, err := template.ParseFiles(templateFile)
+
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	err = tmpl.Execute(w, subdomainRouteMap)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+	}
+}
+
+func panelCheckTargetHealth(w http.ResponseWriter, r *http.Request) {
+	if r.Method != http.MethodHead {
+		http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	targetUrl := r.URL.Query().Get("target")
+
+	if targetUrl == "" {
+		http.Error(w, "target is required", http.StatusBadRequest)
+		return
+	}
+
+	// try HEAD first
+	// if HEAD is not allowed, try GET
+	resp, err := healthCheckHttpClient.Head(targetUrl)
+	if err != nil && resp != nil && resp.StatusCode == http.StatusMethodNotAllowed {
+		_, err = healthCheckHttpClient.Get(targetUrl)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusServiceUnavailable)
+			return
+		}
+	}
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusServiceUnavailable)
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+}