reverseproxy: fix error when remote address is not an IP (#7429)

modules/caddyhttp/reverseproxy/headers_test.go

@@ -0,0 +1,34 @@
+package reverseproxy
+
+import (
+	"context"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+)
+
+func TestAddForwardedHeadersNonIP(t *testing.T) {
+	h := Handler{}
+
+	// Simulate a request with a non-IP remote address (e.g. SCION, abstract socket, or hostname)
+	req := httptest.NewRequest("GET", "/", nil)
+	req.RemoteAddr = "my-weird-network:12345"
+
+	// Mock the context variables required by Caddy.
+	// We need to inject the variable map manually since we aren't running the full server.
+	vars := map[string]interface{}{
+		caddyhttp.TrustedProxyVarKey: false,
+	}
+	ctx := context.WithValue(req.Context(), caddyhttp.VarsCtxKey, vars)
+	req = req.WithContext(ctx)
+
+	// Execute the unexported function
+	err := h.addForwardedHeaders(req)
+
+	// Expectation: No error should be returned for non-IP addresses.
+	// The function should simply skip the trusted proxy check.
+	if err != nil {
+		t.Errorf("expected no error for non-IP address, got: %v", err)
+	}
+}

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -789,16 +789,19 @@ func (h Handler) addForwardedHeaders(req *http.Request) error {
 	// to pull that out before parsing the IP
 	clientIP, _, _ = strings.Cut(clientIP, "%")
 	ipAddr, err := netip.ParseAddr(clientIP)
-	if err != nil {
-		return fmt.Errorf("invalid IP address: '%s': %v", clientIP, err)
-	}
 
 	// Check if the client is a trusted proxy
 	trusted := caddyhttp.GetVar(req.Context(), caddyhttp.TrustedProxyVarKey).(bool)
-	for _, ipRange := range h.trustedProxies {
-		if ipRange.Contains(ipAddr) {
-			trusted = true
-			break
+
+	// If ParseAddr fails (e.g. non-IP network like SCION), we cannot check
+	// if it is a trusted proxy by IP range. In this case, we ignore the
+	// error and treat the connection as untrusted (or retain existing status).
+	if err == nil {
+		for _, ipRange := range h.trustedProxies {
+			if ipRange.Contains(ipAddr) {
+				trusted = true
+				break
+			}
 		}
 	}