Replace strings.Index with strings.Cut (#4932)

cmd/main.go

@@ -408,11 +408,8 @@ func parseEnvFile(envInput io.Reader) (map[string]string, error) {
 		}
 
 		// remove any trailing comment after value
-		if commentStart := strings.Index(val, "#"); commentStart > 0 {
-			before := val[commentStart-1]
-			if before == '\t' || before == ' ' {
-				val = strings.TrimRight(val[:commentStart], " \t")
-			}
+		if commentStart, _, found := strings.Cut(val, "#"); found {
+			val = strings.TrimRight(commentStart, " \t")
 		}
 
 		// quoted value: support newlines

modules/caddyhttp/reverseproxy/reverseproxy.go

@@ -658,8 +658,8 @@ func (h Handler) addForwardedHeaders(req *http.Request) error {
 
 	// Client IP may contain a zone if IPv6, so we need
 	// to pull that out before parsing the IP
-	if idx := strings.IndexByte(clientIP, '%'); idx >= 0 {
-		clientIP = clientIP[:idx]
+	if before, _, found := strings.Cut(clientIP, "%"); found {
+		clientIP = before
 	}
 	ip := net.ParseIP(clientIP)
 	if ip == nil {

modules/caddyhttp/rewrite/rewrite.go

@@ -194,10 +194,10 @@ func (rewr Rewrite) Rewrite(r *http.Request, repl *caddy.Replacer) bool {
 
 		// before continuing, we need to check if a query string
 		// snuck into the path component during replacements
-		if quPos := strings.Index(newPath, "?"); quPos > -1 {
+		if before, after, found := strings.Cut(newPath, "?"); found {
 			// recompute; new path contains a query string
 			var injectedQuery string
-			newPath, injectedQuery = newPath[:quPos], newPath[quPos+1:]
+			newPath, injectedQuery = before, after
 			// don't overwrite explicitly-configured query string
 			if query == "" {
 				query = injectedQuery