BanGUI/backend/tests/test_utils/test_regex_validator.py

"""Tests for regex pattern validation with ReDoS protection."""

from __future__ import annotations

import re

import pytest

from app.utils.regex_validator import (
    MAX_REGEX_LENGTH,
    REGEX_COMPILE_TIMEOUT_SECONDS,
    RegexTimeoutError,
    validate_regex_pattern,
)


class TestValidateRegexPattern:
    """Tests for validate_regex_pattern function."""

    def test_valid_simple_pattern(self) -> None:
        """Valid simple patterns should compile without error."""
        validate_regex_pattern(r"^[a-z]+$")
        validate_regex_pattern(r"\d{3}-\d{3}-\d{4}")
        validate_regex_pattern(r"[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}")

    def test_valid_complex_pattern(self) -> None:
        """Valid complex patterns should compile without error."""
        validate_regex_pattern(r"^(?:[0-9]{1,3}\.){3}[0-9]{1,3}$")
        validate_regex_pattern(r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$")
        validate_regex_pattern(r"^(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)$")

    def test_pattern_exceeds_max_length(self) -> None:
        """Patterns exceeding MAX_REGEX_LENGTH should raise ValueError."""
        # Create pattern exactly at max length (should work)
        max_pattern = "a" * MAX_REGEX_LENGTH
        validate_regex_pattern(max_pattern)

        # Create pattern exceeding max length
        too_long = "a" * (MAX_REGEX_LENGTH + 1)
        with pytest.raises(ValueError, match="exceeds maximum length"):
            validate_regex_pattern(too_long)

    def test_pattern_far_exceeds_max_length(self) -> None:
        """Patterns far exceeding max length should raise ValueError."""
        too_long = "a" * (MAX_REGEX_LENGTH * 2)
        with pytest.raises(ValueError, match="exceeds maximum length"):
            validate_regex_pattern(too_long)

    def test_invalid_syntax_raises_error(self) -> None:
        """Patterns with invalid syntax should raise re.error."""
        with pytest.raises(re.error):
            validate_regex_pattern(r"[unclosed")

        with pytest.raises(re.error):
            validate_regex_pattern(r"(?P<incomplete")

        with pytest.raises(re.error):
            validate_regex_pattern(r"(unclosed")

    def test_empty_pattern(self) -> None:
        """Empty patterns should compile without error."""
        validate_regex_pattern("")

    def test_special_characters_allowed(self) -> None:
        """Patterns with special regex characters should work."""
        validate_regex_pattern(r"\b\w+\b")
        validate_regex_pattern(r"(?:foo|bar|baz)")
        validate_regex_pattern(r"(?P<name>\w+)")

    def test_pattern_length_validation_is_first(self) -> None:
        """Length validation should happen before compilation (faster)."""
        # Create a pattern that is too long and also invalid
        # Should raise ValueError for length, not re.error for syntax
        too_long_and_invalid = "a" * (MAX_REGEX_LENGTH + 1) + r"[unclosed"
        with pytest.raises(ValueError, match="exceeds maximum length"):
            validate_regex_pattern(too_long_and_invalid)

    def test_common_fail2ban_patterns(self) -> None:
        """Common fail2ban regex patterns should validate correctly."""
        # These are real patterns from fail2ban filters
        common_patterns = [
            r"^%(__prefix_line)s(?:error|warn).*Failed (?:password|publickey) for invalid user (?:[^ ]+) from <HOST>",
            r"^%(__prefix_line)s(?:error|warn).*Connection (?:closed|reset) by (?:authenticating )?user .* <HOST>",
            r"^%(__prefix_line)s(?:error|warn).*Invalid user (?:[^ ]+) from <HOST>",
            r"^%(__prefix_line)s(?:error|warn).*Received disconnect from <HOST>",
        ]
        for pattern in common_patterns:
            validate_regex_pattern(pattern)

    def test_pattern_with_lookahead_lookbehind(self) -> None:
        """Patterns with lookahead/lookbehind should work."""
        validate_regex_pattern(r"(?<!abc)def")  # Negative lookbehind
        validate_regex_pattern(r"abc(?!def)")   # Negative lookahead
        validate_regex_pattern(r"(?<=abc)def")  # Positive lookbehind
        validate_regex_pattern(r"abc(?=def)")   # Positive lookahead


class TestRegexTimeoutError:
    """Tests for RegexTimeoutError exception class."""

    def test_regex_timeout_error_message(self) -> None:
        """RegexTimeoutError should have a descriptive message."""
        pattern = r"(a+)+b"
        timeout_seconds = 2
        exc = RegexTimeoutError(pattern, timeout_seconds)
        assert f"{timeout_seconds}s" in str(exc)
        assert "ReDoS" in str(exc)
        assert pattern in str(exc)

    def test_regex_timeout_error_attributes(self) -> None:
        """RegexTimeoutError should store pattern and timeout."""
        pattern = r"(a+)+b"
        timeout_seconds = 2
        exc = RegexTimeoutError(pattern, timeout_seconds)
        assert exc.pattern == pattern
        assert exc.timeout_seconds == timeout_seconds


class TestValidateRegexPatternEdgeCases:
    """Test edge cases and boundary conditions."""

    def test_pattern_with_null_bytes(self) -> None:
        """Patterns with null bytes should still validate (if compilable)."""
        # This may or may not work depending on Python version
        # but shouldn't cause a crash
        try:
            validate_regex_pattern("a\x00b")
        except (ValueError, re.error):
            pass  # Either error is acceptable

    def test_pattern_with_unicode(self) -> None:
        """Patterns with Unicode characters should work."""
        validate_regex_pattern(r"[α-ω]+")
        validate_regex_pattern(r"café")
        validate_regex_pattern(r"日本語")

    def test_unicode_pattern_within_length_limit(self) -> None:
        """Unicode patterns should count by character, not bytes."""
        # Create a long unicode pattern that's under character limit
        unicode_pattern = "ア" * (MAX_REGEX_LENGTH - 1)
        validate_regex_pattern(unicode_pattern)

        # Exceeding character limit should fail
        unicode_pattern_long = "ア" * (MAX_REGEX_LENGTH + 1)
        with pytest.raises(ValueError, match="exceeds maximum length"):
            validate_regex_pattern(unicode_pattern_long)

    def test_pattern_repeated_at_boundary(self) -> None:
        """Pattern at exact boundary should work."""
        boundary_pattern = "a" * MAX_REGEX_LENGTH
        validate_regex_pattern(boundary_pattern)

        just_over = "a" * (MAX_REGEX_LENGTH + 1)
        with pytest.raises(ValueError):
            validate_regex_pattern(just_over)