#8: implement ManageSieve protocol server (RFC 5804)

services/protocols/internal/domain/entity/sieve_validator.go

@@ -0,0 +1,117 @@
+package entity
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+)
+
+var (
+	ErrEmptyScript       = errors.New("sieve script cannot be empty")
+	ErrUnmatchedBrace    = errors.New("unmatched curly brace in sieve script")
+	ErrUnmatchedBracket  = errors.New("unmatched square bracket in sieve script")
+	ErrUnterminatedQuote = errors.New("unterminated string literal in sieve script")
+	ErrUnterminatedComment = errors.New("unterminated comment block in sieve script")
+)
+
+// ValidateSieveScript performs structural syntax validation of an RFC 5228 Sieve script.
+func ValidateSieveScript(script string) error {
+	trimmed := strings.TrimSpace(script)
+	if trimmed == "" {
+		return ErrEmptyScript
+	}
+
+	var braceCount int
+	var bracketCount int
+	inSingleQuote := false
+	inMultiComment := false
+	inString := false
+
+	runes := []rune(script)
+	n := len(runes)
+
+	for i := 0; i < n; i++ {
+		r := runes[i]
+
+		// Handle multi-line comment /* ... */
+		if inMultiComment {
+			if r == '*' && i+1 < n && runes[i+1] == '/' {
+				inMultiComment = false
+				i++
+			}
+			continue
+		}
+
+		// Handle string literal "..."
+		if inString {
+			if r == '\\' {
+				i++ // skip escaped char
+				continue
+			}
+			if r == '"' {
+				inString = false
+			}
+			continue
+		}
+
+		// Handle single line comment # ...
+		if inSingleQuote {
+			if r == '\n' {
+				inSingleQuote = false
+			}
+			continue
+		}
+
+		// Detect start of comment /*
+		if r == '/' && i+1 < n && runes[i+1] == '*' {
+			inMultiComment = true
+			i++
+			continue
+		}
+
+		// Detect start of comment #
+		if r == '#' {
+			inSingleQuote = true
+			continue
+		}
+
+		// Detect start of string "
+		if r == '"' {
+			inString = true
+			continue
+		}
+
+		// Track braces & brackets
+		switch r {
+		case '{':
+			braceCount++
+		case '}':
+			braceCount--
+			if braceCount < 0 {
+				return ErrUnmatchedBrace
+			}
+		case '[':
+			bracketCount++
+		case ']':
+			bracketCount--
+			if bracketCount < 0 {
+				return ErrUnmatchedBracket
+			}
+		}
+	}
+
+	if inMultiComment {
+		return ErrUnterminatedComment
+	}
+	if inString {
+		return ErrUnterminatedQuote
+	}
+	if braceCount != 0 {
+		return fmt.Errorf("%w: balance is %d", ErrUnmatchedBrace, braceCount)
+	}
+	if bracketCount != 0 {
+		return fmt.Errorf("%w: balance is %d", ErrUnmatchedBracket, bracketCount)
+	}
+
+	return nil
+}