fix: rate limiting X-Real-IP from the real peer

api/middleware/trustedProxyRealIP.go

@@ -0,0 +1,44 @@
+package middleware
+
+import (
+	"net"
+	"net/http"
+)
+
+func TrustedProxyRealIP(trustedProxies []string) func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			realIP := r.Header.Get("X-Real-IP")
+			if realIP != "" && isTrustedProxy(r.RemoteAddr, trustedProxies) {
+				r.RemoteAddr = withRewrittenHost(r.RemoteAddr, realIP)
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}
+
+func isTrustedProxy(remoteAddr string, trustedProxies []string) bool {
+	host := hostOf(remoteAddr)
+	for _, trusted := range trustedProxies {
+		if host == trusted {
+			return true
+		}
+	}
+	return false
+}
+
+func hostOf(remoteAddr string) string {
+	host, _, err := net.SplitHostPort(remoteAddr)
+	if err != nil {
+		return remoteAddr
+	}
+	return host
+}
+
+func withRewrittenHost(remoteAddr string, newHost string) string {
+	_, port, err := net.SplitHostPort(remoteAddr)
+	if err != nil {
+		return newHost
+	}
+	return net.JoinHostPort(newHost, port)
+}