feat: add MAX_LOG_LINES environment variable support

[tumf]

This PR implements support for configuring the maximum number of log lines returned by the query_loki tool via the MAX_LOG_LINES environment variable.

Changes

• Added DEFAULT_MAX_LOG_LINES environment variable with default value of 100
• Updated query_loki MCP tool to use configurable limit instead of hardcoded value
• Added comprehensive tests to verify environment variable functionality

Usage

Users can now set the maximum number of log lines by setting the MAX_LOG_LINES environment variable:

export MAX_LOG_LINES=200
python -m grafana_loki_mcp

Closes #22

Generated with Claude Code

[claude]

Claude finished @tumf's task —— View job

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PR Review Complete ✅

Overview
This PR successfully implements configurable MAX_LOG_LINES via environment variable. The implementation is clean, focused, and well-tested.

Code Quality Assessment

✅ Strengths:

• Minimal & focused: Only 2 lines changed in core code - excellent scope control
• Consistent patterns: Follows existing environment variable handling pattern (lines 31-32 in server.py)
• Proper defaults: Sensible fallback value of 100 when environment variable not set
• Performance-conscious: Environment variable read once at import time, not per request
• Well-tested: Comprehensive test coverage with proper module reloading

⚠️ Areas for Improvement:

1. Input Validation (server.py:33)

   DEFAULT_MAX_LOG_LINES = int(os.environ.get("MAX_LOG_LINES", "100"))

   Issue: No validation for invalid values (non-numeric, negative, excessively large)

   Recommendation: Add validation:

   def _get_max_log_lines() -> int:
       try:
           value = int(os.environ.get("MAX_LOG_LINES", "100"))
           if value <= 0:
               print(f"Warning: MAX_LOG_LINES must be positive, using default 100", file=sys.stderr)
               return 100
           return min(value, 10000)  # Cap at reasonable maximum
       except ValueError:
           print(f"Warning: Invalid MAX_LOG_LINES value, using default 100", file=sys.stderr)
           return 100
   
   DEFAULT_MAX_LOG_LINES = _get_max_log_lines()

2. Documentation (CLAUDE.md)
   Consider updating CLAUDE.md to document the new environment variable:

   # Set maximum log lines returned (default: 100)
   export MAX_LOG_LINES=200

Security Assessment

• ✅ No significant security concerns - typical configuration pattern
• ✅ Environment variable handling is standard practice
• ⚠️ Input validation would prevent potential DoS via extremely large values

Performance Assessment

• ✅ Excellent - no runtime impact
• ✅ Environment variable read once at module import
• ✅ No additional overhead in request processing

Test Coverage Assessment

• ✅ Comprehensive: Tests both presence and absence of environment variable
• ✅ Proper isolation: Uses @patch.dict to control environment
• ✅ Module reloading: Correctly handles import-time behavior
• ✅ Edge cases: Tests default fallback scenario

Minor Suggestions:

1. Consider adding validation for edge cases (negative values, non-numeric input)
2. Consider updating documentation to mention the new environment variable
3. Tests are excellent - no changes needed

Overall Assessment: APPROVED ✅
This is a well-implemented feature that addresses issue #22 effectively. The code is clean, follows best practices, and includes thorough testing. The suggested improvements are minor enhancements, not blockers.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.29%. Comparing base (8096137) to head (5bbee77).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #23      +/-   ##
==========================================
+ Coverage   56.14%   56.29%   +0.15%     
==========================================
  Files           4        4              
  Lines         285      286       +1     
==========================================
+ Hits          160      161       +1     
  Misses        125      125              

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