Fix rehandling bug

modules/caddyhttp/caddyhttp.go

@@ -85,6 +85,10 @@ func (app *App) Provision(ctx caddy.Context) error {
 				return fmt.Errorf("setting up server error handling routes: %v", err)
 			}
 		}
+
+		if srv.MaxRehandles == nil {
+			srv.MaxRehandles = &DefaultMaxRehandles
+		}
 	}
 
 	return nil
@@ -111,8 +115,8 @@ func (app *App) Validate() error {
 
 	// each server's max rehandle value must be valid
 	for srvName, srv := range app.Servers {
-		if srv.MaxRehandles < 0 {
+		if srv.MaxRehandles != nil && *srv.MaxRehandles < 0 {
-			return fmt.Errorf("%s: invalid max_rehandles value: %d", srvName, srv.MaxRehandles)
+			return fmt.Errorf("%s: invalid max_rehandles value: %d", srvName, *srv.MaxRehandles)
 		}
 	}
 
@@ -435,6 +439,10 @@ const (
 	DefaultHTTPSPort = 443
 )
 
+// DefaultMaxRehandles is the maximum number of rehandles to
+// allow, if not specified explicitly.
+var DefaultMaxRehandles = 3
+
 // Interface guards
 var (
 	_ caddy.App         = (*App)(nil)

modules/caddyhttp/server.go

@@ -39,7 +39,7 @@ type Server struct {
 	Errors            *HTTPErrorConfig            `json:"errors,omitempty"`
 	TLSConnPolicies   caddytls.ConnectionPolicies `json:"tls_connection_policies,omitempty"`
 	AutoHTTPS         *AutoHTTPSConfig            `json:"automatic_https,omitempty"`
-	MaxRehandles      int                         `json:"max_rehandles,omitempty"`
+	MaxRehandles      *int                        `json:"max_rehandles,omitempty"`
 	StrictSNIHost     bool                        `json:"strict_sni_host,omitempty"` // TODO: see if we can turn this on by default when clientauth is configured
 
 	tlsApp *caddytls.TLS
@@ -65,9 +65,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	addHTTPVarsToReplacer(repl, r, w)
 
 	// build and execute the main handler chain
-	stack := s.Routes.BuildCompositeRoute(r)
+	err := s.executeCompositeRoute(w, r, s.Routes)
-	stack = s.wrapPrimaryRoute(stack)
-	err := s.executeCompositeRoute(w, r, stack)
 	if err != nil {
 		// add the raw error value to the request context
 		// so it can be accessed by error handlers
@@ -85,8 +83,7 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		}
 
 		if s.Errors != nil && len(s.Errors.Routes) > 0 {
-			errStack := s.Errors.Routes.BuildCompositeRoute(r)
+			err := s.executeCompositeRoute(w, r, s.Errors.Routes)
-			err := s.executeCompositeRoute(w, r, errStack)
 			if err != nil {
 				// TODO: what should we do if the error handler has an error?
 				log.Printf("[ERROR] [%s %s] handling error: %v", r.Method, r.RequestURI, err)
@@ -103,20 +100,33 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
-// executeCompositeRoute executes stack with w and r. This function handles
+// executeCompositeRoute compiles a composite route from routeList and executes
-// the special ErrRehandle error value, which reprocesses requests through
+// it using w and r. This function handles the sentinel ErrRehandle error value,
-// the stack again. Any error value returned from this function would be an
+// which reprocesses requests through the stack again. Any error value returned
-// actual error that needs to be handled.
+// from this function would be an actual error that needs to be handled.
-func (s *Server) executeCompositeRoute(w http.ResponseWriter, r *http.Request, stack Handler) error {
+func (s *Server) executeCompositeRoute(w http.ResponseWriter, r *http.Request, routeList RouteList) error {
+	maxRehandles := 0
+	if s.MaxRehandles != nil {
+		maxRehandles = *s.MaxRehandles
+	}
 	var err error
-	for i := -1; i <= s.MaxRehandles; i++ {
+	for i := -1; i <= maxRehandles; i++ {
 		// we started the counter at -1 because we
 		// always want to run this at least once
+
+		// the purpose of rehandling is often to give
+		// matchers a chance to re-evaluate on the
+		// changed version of the request, so compile
+		// the handler stack anew in each iteration
+		stack := routeList.BuildCompositeRoute(r)
+		stack = s.wrapPrimaryRoute(stack)
+
+		// only loop if rehandling is required
 		err = stack.ServeHTTP(w, r)
 		if err != ErrRehandle {
 			break
 		}
-		if i >= s.MaxRehandles-1 {
+		if i >= maxRehandles-1 {
 			return fmt.Errorf("too many rehandles")
 		}
 	}