fix(subrouter): strip regex source from pattern prefix in Sub (#108)

Author: tigerwill90

fox.go

@@ -12,6 +12,7 @@ import (
 	"net"
 	"net/http"
 	"path"
+	"regexp"
 	"slices"
 	"strings"
 	"sync"
@@ -975,15 +976,24 @@ func Sub(router *Router) HandlerFunc {
 
 		*subCtx.subPatterns = append(*subCtx.subPatterns, *c.subPatterns...)
 
-		lastTkType := route.pattern.tokens[len(route.pattern.tokens)-1].typ
+		lastTk := route.pattern.tokens[len(route.pattern.tokens)-1]
 		var p string
-		switch lastTkType {
+		switch lastTk.typ {
 		case nodeWildcard:
 			key := (*c.paramsKeys)[len(*c.paramsKeys)-1]
-			p = strings.TrimSuffix(c.pattern[:len(c.pattern)-(len(key)+wildcardExtraChar)], "/")
+			extra := len(key) + wildcardExtraChar
+			if lastTk.regexp != nil {
+				// +1 for the ':' separator between name and regex source.
+				extra += 1 + len(rawExpr(lastTk.regexp))
+			}
+			p = strings.TrimSuffix(c.pattern[:len(c.pattern)-extra], "/")
 		case nodeParam:
 			key := (*c.paramsKeys)[len(*c.paramsKeys)-1]
-			p = strings.TrimSuffix(c.pattern[:len(c.pattern)-(len(key)+paramExtraChar)], "/")
+			extra := len(key) + paramExtraChar
+			if lastTk.regexp != nil {
+				extra += 1 + len(rawExpr(lastTk.regexp))
+			}
+			p = strings.TrimSuffix(c.pattern[:len(c.pattern)-extra], "/")
 		default:
 			// Reaching this case means the parent route does not end with a catch-all parameter (e.g., /api/
 			// instead of /api/+{rest}). This is technically a misuse of the sub-router API, but we handle it
@@ -1124,3 +1134,8 @@ func firstHeader(headers http.Header, k string) (string, bool) {
 	}
 	return v[0], true
 }
+
+func rawExpr(re *regexp.Regexp) string {
+	expr := re.String()
+	return expr[4 : len(expr)-2]
+}

fox_test.go

@@ -1478,6 +1478,34 @@ func TestRouter_ServeHTTP_HandleSubRouter(t *testing.T) {
 		assert.Equal(t, http.StatusNotFound, w.Code)
 	})
 
+	t.Run("sub-router registered with regex wildcard", func(t *testing.T) {
+		sub := MustRouter()
+		sub.MustAdd(MethodGet, "/users", patternHandler)
+
+		fx := MustRouter(AllowRegexpParam(true))
+		require.NoError(t, onlyError(fx.Add(MethodGet, "/api/+{rest:[a-z]+}", Sub(sub))))
+
+		req := httptest.NewRequest(http.MethodGet, "/api/users", nil)
+		w := httptest.NewRecorder()
+		fx.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusOK, w.Code)
+		assert.Equal(t, "/api/users", w.Body.String())
+	})
+
+	t.Run("sub-router registered with regex param", func(t *testing.T) {
+		sub := MustRouter()
+		sub.MustAdd(MethodGet, "/users", patternHandler)
+
+		fx := MustRouter(AllowRegexpParam(true))
+		require.NoError(t, onlyError(fx.Add(MethodGet, "/api/{name:[a-z]+}", Sub(sub))))
+
+		req := httptest.NewRequest(http.MethodGet, "/api/users", nil)
+		w := httptest.NewRecorder()
+		fx.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusOK, w.Code)
+		assert.Equal(t, "/api/users", w.Body.String())
+	})
+
 	t.Run("sub-router no route handler sees clean context", func(t *testing.T) {
 		var pat, tenant string
 		var route *Route

matcher.go

@@ -110,8 +110,7 @@ func (m QueryRegexpMatcher) Key() string {
 
 // Value returns the regular expression matching the query parameter.
 func (m QueryRegexpMatcher) Value() string {
-	expr := m.regex.String()
-	return expr[4 : len(expr)-2]
+	return rawExpr(m.regex)
 }
 
 // String returns a textual representation of the matcher in the form "qx:key=expr".
@@ -224,8 +223,7 @@ func (m HeaderRegexpMatcher) Key() string {
 
 // Value returns the regular expression matching the header.
 func (m HeaderRegexpMatcher) Value() string {
-	expr := m.regex.String()
-	return expr[4 : len(expr)-2]
+	return rawExpr(m.regex)
 }
 
 // Match reports whether the request contains the configured header with any value matching the configured regular

tree.go

@@ -953,9 +953,7 @@ func concat(a, b string) string {
 // placeholder ("?" for params, "*" for catch-alls).
 func canonicalKey(tk token) string {
 	if tk.regexp != nil {
-		// Strip the surrounding ^(?: and )$ added by compileParamRegexp.
-		expr := tk.regexp.String()
-		return expr[4 : len(expr)-2]
+		return rawExpr(tk.regexp)
 	}
 	switch tk.typ {
 	case nodeParam: