Encode checkpoint and debug path identities

internal/core/fileio/fileio.go

@@ -10,6 +10,38 @@ import (
 	"strings"
 )
 
+// EncodePathComponent returns a filesystem-safe, injective representation of
+// one logical path component.
+func EncodePathComponent(value string) string {
+	if value == "" {
+		return "%"
+	}
+
+	const hexadecimal = "0123456789ABCDEF"
+	var out strings.Builder
+	for index := 0; index < len(value); index++ {
+		byteValue := value[index]
+		switch {
+		case byteValue >= 'a' && byteValue <= 'z', byteValue >= 'A' && byteValue <= 'Z', byteValue >= '0' && byteValue <= '9', byteValue == '-', byteValue == '_':
+			out.WriteByte(byteValue)
+		case byteValue == '.' && safePathDot(value, index):
+			out.WriteByte(byteValue)
+		default:
+			out.WriteByte('%')
+			out.WriteByte(hexadecimal[byteValue>>4])
+			out.WriteByte(hexadecimal[byteValue&0x0f])
+		}
+	}
+	return out.String()
+}
+
+func safePathDot(value string, index int) bool {
+	if value == "." || value == ".." {
+		return false
+	}
+	return (index == 0 || value[index-1] != '.') && (index+1 == len(value) || value[index+1] != '.')
+}
+
 func SafePath(root, name string) (string, error) {
 	root = strings.TrimSpace(root)
 	if root == "" {