Gondulf/docs/reports/2025-11-22-dns-verification-bug-fix.md

# Implementation Report: DNS Verification Bug Fix

**Date**: 2025-11-22
**Developer**: Claude (Developer Agent)
**Design Reference**: /docs/designs/dns-verification-bug-fix.md

## Summary

Fixed a critical bug in the DNS TXT record verification that caused domain verification to always fail. The code was querying the base domain (e.g., `example.com`) instead of the `_gondulf.{domain}` subdomain (e.g., `_gondulf.example.com`) where users are instructed to place their TXT records. The fix modifies the `verify_txt_record` method in `src/gondulf/dns.py` to prefix the domain with `_gondulf.` when the expected value is `gondulf-verify-domain`. All tests pass with 100% coverage on the DNS module.

## What Was Implemented

### Components Modified

1. **`src/gondulf/dns.py`** - DNSService class
   - Modified `verify_txt_record` method to query the correct subdomain
   - Updated docstring to document the Gondulf-specific behavior
   - Updated all logging statements to include both the requested domain and the queried domain

2. **`tests/unit/test_dns.py`** - DNS unit tests
   - Added new test class `TestGondulfDomainVerification` with 7 test cases
   - Tests verify the critical bug fix behavior
   - Tests ensure backward compatibility for non-Gondulf TXT verification

### Key Implementation Details

The fix implements Option A from the design document - modifying the existing `verify_txt_record` method rather than creating a new dedicated method. This keeps the fix localized and maintains backward compatibility.

**Core logic added:**
```python
# For Gondulf domain verification, query _gondulf subdomain
if expected_value == "gondulf-verify-domain":
    query_domain = f"_gondulf.{domain}"
else:
    query_domain = domain
```

**Logging updates:**
- Success log now shows: `"TXT record verification successful for domain={domain} (queried {query_domain})"`
- Failure log now shows: `"TXT record verification failed: expected value not found for domain={domain} (queried {query_domain})"`
- Error log now shows: `"TXT record verification failed for domain={domain} (queried {query_domain}): {e}"`

## How It Was Implemented

### Approach

1. **Reviewed design document** - Confirmed Option A (modify existing method) was the recommended approach
2. **Reviewed standards** - Checked coding.md and testing.md for requirements
3. **Implemented the fix** - Single edit to `verify_txt_record` method
4. **Added comprehensive tests** - Created new test class covering all scenarios from design
5. **Ran full test suite** - Verified no regressions

### Deviations from Design

No deviations from design.

The implementation follows the design document exactly:
- Used Option A (modify `verify_txt_record` method)
- Added the domain prefixing logic as specified
- Updated logging to show both domains
- No changes needed to authorization router or templates

## Issues Encountered

No significant issues encountered.

The fix was straightforward as designed. The existing code structure made the change clean and isolated.

## Test Results

### Test Execution

```
============================= test session starts ==============================
platform linux -- Python 3.11.14, pytest-9.0.1, pluggy-1.6.0
plugins: anyio-4.11.0, asyncio-1.3.0, mock-3.15.1, cov-7.0.0, Faker-38.2.0
collected 487 items

[... all tests ...]

================= 482 passed, 5 skipped, 36 warnings in 20.00s =================
```

### Test Coverage

- **Overall Coverage**: 90.44%
- **DNS Module Coverage**: 100% (`src/gondulf/dns.py`)
- **Coverage Tool**: pytest-cov 7.0.0

### Test Scenarios

#### New Unit Tests Added (TestGondulfDomainVerification)

1. **test_gondulf_verification_queries_prefixed_subdomain** - Critical test verifying the bug fix
   - Verifies `verify_txt_record("example.com", "gondulf-verify-domain")` queries `_gondulf.example.com`

2. **test_gondulf_verification_with_missing_txt_record** - Tests NoAnswer handling
   - Verifies returns False when no TXT records exist at `_gondulf.{domain}`

3. **test_gondulf_verification_with_wrong_txt_value** - Tests value mismatch
   - Verifies returns False when TXT value doesn't match

4. **test_non_gondulf_verification_queries_base_domain** - Backward compatibility test
   - Verifies other TXT verification still queries base domain (not prefixed)

5. **test_gondulf_verification_with_nxdomain** - Tests NXDOMAIN handling
   - Verifies returns False when `_gondulf.{domain}` doesn't exist

6. **test_gondulf_verification_among_multiple_txt_records** - Tests multi-record scenarios
   - Verifies correct value found among multiple TXT records

7. **test_gondulf_verification_with_subdomain** - Tests subdomain handling
   - Verifies `blog.example.com` queries `_gondulf.blog.example.com`

#### Existing Tests (All Pass)

All 22 existing DNS tests continue to pass, confirming no regressions:
- TestDNSServiceInit (1 test)
- TestGetTxtRecords (7 tests)
- TestVerifyTxtRecord (7 tests)
- TestCheckDomainExists (5 tests)
- TestResolverFallback (2 tests)

### Test Results Analysis

- All 29 DNS tests pass (22 existing + 7 new)
- 100% coverage on dns.py module
- Full test suite (487 tests) passes with no regressions
- 5 skipped tests are unrelated (SQL injection tests awaiting implementation)
- Deprecation warnings are unrelated to this change (FastAPI/Starlette lifecycle patterns)

## Technical Debt Created

No technical debt identified.

The fix is clean, well-tested, and follows the existing code patterns. The implementation matches the design exactly.

## Next Steps

1. **Manual Testing** - Per the design document, manual testing with a real DNS record is recommended:
   - Configure real DNS record: `_gondulf.yourdomain.com` with value `gondulf-verify-domain`
   - Test authorization flow
   - Verify successful DNS verification
   - Check logs show correct domain being queried

2. **Deployment** - This is a P0 critical bug fix that should be deployed to production as soon as testing is complete.

## Sign-off

Implementation status: Complete
Ready for Architect review: Yes