feat(logging): add JSON log config and formatter (#27)

src/quartermaster/logconfig.json

@@ -0,0 +1,59 @@
+{
+  "version": 1,
+  "disable_existing_loggers": false,
+  "formatters": {
+    "json": {
+      "()": "pythonjsonlogger.jsonlogger.JsonFormatter",
+      "fmt": "%(asctime)s %(levelname)s %(name)s %(message)s",
+      "rename_fields": {
+        "asctime": "timestamp",
+        "levelname": "level",
+        "name": "logger"
+      }
+    }
+  },
+  "filters": {
+    "access": {
+      "()": "quartermaster.logging_config.AccessLogFilter"
+    }
+  },
+  "handlers": {
+    "stdout": {
+      "class": "logging.StreamHandler",
+      "stream": "ext://sys.stdout",
+      "formatter": "json"
+    },
+    "access": {
+      "class": "logging.StreamHandler",
+      "stream": "ext://sys.stdout",
+      "formatter": "json",
+      "filters": ["access"]
+    }
+  },
+  "loggers": {
+    "quartermaster": {
+      "level": "INFO",
+      "handlers": ["stdout"],
+      "propagate": false
+    },
+    "uvicorn": {
+      "level": "INFO",
+      "handlers": ["stdout"],
+      "propagate": false
+    },
+    "uvicorn.error": {
+      "level": "INFO",
+      "handlers": ["stdout"],
+      "propagate": false
+    },
+    "uvicorn.access": {
+      "level": "INFO",
+      "handlers": ["access"],
+      "propagate": false
+    }
+  },
+  "root": {
+    "level": "INFO",
+    "handlers": ["stdout"]
+  }
+}

src/quartermaster/logging_config.py

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+from __future__ import annotations
+
+import json
+import logging
+from pathlib import Path
+
+_CONFIG_PATH = Path(__file__).parent / "logconfig.json"
+LOG_CONFIG = json.loads(_CONFIG_PATH.read_text())
+
+
+class AccessLogFilter(logging.Filter):
+    """Enrich uvicorn access records with structured fields for Loki.
+
+    Uvicorn emits access records whose ``args`` tuple is
+    ``(client_addr, method, full_path, http_version, status_code)``.
+    """
+
+    def filter(self, record: logging.LogRecord) -> bool:
+        args = record.args
+        if isinstance(args, tuple) and len(args) >= 5:
+            record.event = "http_request"
+            record.client_ip = args[0]
+            record.method = args[1]
+            record.path = args[2]
+            record.status = args[4]
+        return True

tests/test_logging.py

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+from __future__ import annotations
+
+import io
+import json
+import logging
+
+from quartermaster.logging_config import LOG_CONFIG
+
+
+def _build_formatter():
+    """Instantiate the JSON formatter from LOG_CONFIG for direct testing."""
+    from pydoc import locate
+
+    cfg = dict(LOG_CONFIG["formatters"]["json"])
+    factory_path = cfg.pop("()")
+    factory = locate(factory_path)
+    assert factory is not None, f"formatter factory not importable: {factory_path}"
+    return factory(**cfg)
+
+
+def test_log_config_emits_json_with_required_fields():
+    formatter = _build_formatter()
+    stream = io.StringIO()
+    handler = logging.StreamHandler(stream)
+    handler.setFormatter(formatter)
+
+    logger = logging.getLogger("tests.logging_smoke")
+    logger.handlers = [handler]
+    logger.propagate = False
+    logger.setLevel(logging.INFO)
+
+    logger.info("smoke message", extra={"event": "smoke"})
+
+    line = stream.getvalue().strip()
+    assert line, "formatter produced no output"
+    payload = json.loads(line)
+
+    assert payload["event"] == "smoke"
+    assert payload["level"] == "INFO"
+    assert payload["logger"] == "tests.logging_smoke"
+    assert payload["message"] == "smoke message"
+    assert "timestamp" in payload