Add always-forward config to proxy server

cmd/litefs/config.go

@@ -120,6 +120,7 @@ type ProxyConfig struct {
 	MaxLag                 time.Duration `yaml:"max-lag"`
 	Debug                  bool          `yaml:"debug"`
 	Passthrough            []string      `yaml:"passthrough"`
+	AlwaysForward          []string      `yaml:"always-forward"`
 	PrimaryRedirectTimeout time.Duration `yaml:"primary-redirect-timeout"`
 }
 

cmd/litefs/mount_linux.go

@@ -522,13 +522,24 @@ func (c *MountCommand) runProxyServer(ctx context.Context) error {
 		passthroughs = append(passthroughs, re)
 	}
 
+	// Parse always-forward expressions.
+	var alwaysForward []*regexp.Regexp
+	for _, s := range c.Config.Proxy.AlwaysForward {
+		re, err := http.CompileMatch(s)
+		if err != nil {
+			return fmt.Errorf("cannot parse proxy always-forward expression: %q", s)
+		}
+		alwaysForward = append(alwaysForward, re)
+	}
+
 	server := http.NewProxyServer(c.Store)
 	server.Target = c.Config.Proxy.Target
 	server.DBName = c.Config.Proxy.DB
 	server.Addr = c.Config.Proxy.Addr
 	server.MaxLag = c.Config.Proxy.MaxLag
 	server.Debug = c.Config.Proxy.Debug
 	server.Passthroughs = passthroughs
+	server.AlwaysForward = alwaysForward
 	server.PrimaryRedirectTimeout = c.Config.Proxy.PrimaryRedirectTimeout
 	if err := server.Listen(); err != nil {
 		return err

http/proxy_server.go

@@ -58,6 +58,9 @@ type ProxyServer struct {
 	// List of path expressions that will be passed through if matched.
 	Passthroughs []*regexp.Regexp
 
+	// List of path expressions that will always be redirected to the primary.
+	AlwaysForward []*regexp.Regexp
+
 	// If true, add verbose debug logging.
 	Debug bool
 
@@ -184,14 +187,18 @@ func (s *ProxyServer) serveHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	switch r.Method {
-	case http.MethodGet:
-		s.serveRead(w, r)
-	case http.MethodHead:
+	isReadOnly := r.Method == http.MethodGet || r.Method == http.MethodHead
+
+	// Override if path is configured to always forward.
+	if isReadOnly && s.isAlwaysForwarded(r) {
+		isReadOnly = false
+	}
+
+	if isReadOnly {
 		s.serveRead(w, r)
-	default:
-		s.serveNonRead(w, r)
+		return
 	}
+	s.serveNonRead(w, r)
 }
 
 func (s *ProxyServer) serveGetHealth(w http.ResponseWriter, r *http.Request) {
@@ -337,6 +344,16 @@ func (s *ProxyServer) isPassthrough(r *http.Request) bool {
 	return false
 }
 
+// isAlwaysForwarded returns true if request matches any of the redirection expressions.
+func (s *ProxyServer) isAlwaysForwarded(r *http.Request) bool {
+	for _, re := range s.AlwaysForward {
+		if re.MatchString(r.URL.Path) {
+			return true
+		}
+	}
+	return false
+}
+
 // logf logs if debug logging is enabled.
 func (s *ProxyServer) logf(format string, v ...any) {
 	if s.Debug {