services/correlation.py

"""Request correlation ID middleware.

Injects X-Request-ID into every request/response, binds to structlog context
and OpenTelemetry span for distributed trace correlation.
"""

import uuid

import structlog
from fastapi import Request
from starlette.middleware.base import BaseHTTPMiddleware


class CorrelationMiddleware(BaseHTTPMiddleware):
    async def dispatch(self, request: Request, call_next):
        request_id = request.headers.get("X-Request-ID") or str(uuid.uuid4())

        # Bind to structlog for this request's log output
        structlog.contextvars.clear_contextvars()
        structlog.contextvars.bind_contextvars(request_id=request_id)

        # Add to OpenTelemetry span if available
        try:
            from opentelemetry import trace

            span = trace.get_current_span()
            if span.is_recording():
                span.set_attribute("http.request_id", request_id)
        except Exception:
            pass

        response = await call_next(request)
        response.headers["X-Request-ID"] = request_id
        return response