Merge Conflicts (#41)

Co-authored-by: Sayan Datta <sayan@Sayans-MacBook-Air.local>
Reviewed-on: #41

backend/observability.py

@@ -0,0 +1,103 @@
+from __future__ import annotations
+
+import logging
+import time
+import uuid
+from collections import deque
+from dataclasses import asdict, dataclass
+
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.requests import Request
+from starlette.responses import Response
+
+logger = logging.getLogger("velocity.observability")
+
+
+@dataclass(frozen=True)
+class RequestMetric:
+    request_id: str
+    method: str
+    path: str
+    status_code: int
+    duration_ms: float
+
+
+class RequestObservabilityMiddleware(BaseHTTPMiddleware):
+    def __init__(self, app, *, max_metrics: int = 500) -> None:
+        super().__init__(app)
+        self.max_metrics = max_metrics
+
+    async def dispatch(self, request: Request, call_next):
+        request_id = request.headers.get("x-request-id") or str(uuid.uuid4())
+        request.state.request_id = request_id
+        started = time.perf_counter()
+        status_code = 500
+
+        try:
+            response = await call_next(request)
+            status_code = response.status_code
+            return self._finalize(request, response, request_id, started, status_code)
+        except Exception:
+            duration_ms = (time.perf_counter() - started) * 1000
+            self._record_metric(request, request_id, status_code, duration_ms)
+            logger.exception(
+                "request_failed",
+                extra={
+                    "request_id": request_id,
+                    "method": request.method,
+                    "path": request.url.path,
+                    "duration_ms": round(duration_ms, 2),
+                },
+            )
+            raise
+
+    def _finalize(
+        self,
+        request: Request,
+        response: Response,
+        request_id: str,
+        started: float,
+        status_code: int,
+    ) -> Response:
+        duration_ms = (time.perf_counter() - started) * 1000
+        response.headers["X-Request-ID"] = request_id
+        response.headers["X-Response-Time-Ms"] = f"{duration_ms:.2f}"
+        self._record_metric(request, request_id, status_code, duration_ms)
+        logger.info(
+            "request_completed",
+            extra={
+                "request_id": request_id,
+                "method": request.method,
+                "path": request.url.path,
+                "status_code": status_code,
+                "duration_ms": round(duration_ms, 2),
+            },
+        )
+        return response
+
+    def _record_metric(
+        self,
+        request: Request,
+        request_id: str,
+        status_code: int,
+        duration_ms: float,
+    ) -> None:
+        metrics = getattr(request.app.state, "request_metrics", None)
+        if metrics is None:
+            metrics = deque(maxlen=self.max_metrics)
+            request.app.state.request_metrics = metrics
+        metrics.append(
+            RequestMetric(
+                request_id=request_id,
+                method=request.method,
+                path=request.url.path,
+                status_code=status_code,
+                duration_ms=round(duration_ms, 2),
+            )
+        )
+
+
+def metrics_snapshot(app, *, limit: int = 50) -> list[dict]:
+    metrics = getattr(app.state, "request_metrics", deque())
+    return [asdict(metric) for metric in list(metrics)[-limit:]][::-1]
+