request path

Walk of GET /alice/stats with Redis on. Same CacheRateLimitMiddleware as the rest of the family. platform="gfg".

1. CORS middleware (added first, runs second).
2. CacheRateLimitMiddleware with platform="gfg" (added last, runs first).
3. Skip check. Path is not /, /docs, /redoc, /openapi.json, /favicon.ico. Method is GET. Redis is on.
4. Handle is the first path segment, lowercased: alice. A segment with a . is skipped, so favicon.ico never becomes a handle.
5. Cache key is cache:gfg:{sha256(GET:/alice/stats:sorted_query)}.
6. On HIT, body is base64-decoded and returned with X-Cache: HIT. Done.
7. Negative key invalid:gfg:alice. On HIT, HTTP 404 User does not exist, X-Cache: NEGATIVE-HIT. Invalid-user rate limits apply (10/IP and 5/handle per 10 minutes).
8. Live limits: 60 req/min per IP, 30 req/min per handle. Over: 429 with Retry-After and exponential backoff 5s to 300s.
9. Route get_stats hits authapi for the profile and practiceapi for submissions, then stats_from plus build_topic_analysis.
10. make_envelope wraps it. HTTP 200 cached for 3600s unless Cache-Control says otherwise. X-Cache: MISS.

Without Redis, steps 5 to 8 disappear. Every GET hits GFG. Rate limits disappear too. That is fine on a laptop and noisy on a public host.

Tag cache _TAG_CACHE is process-local and independent of Redis. Problem tags do not change often, so they survive a Redis miss.

sequenceDiagram
  participant B as Browser
  participant MW as CacheRateLimit
  participant R as Redis
  participant RT as stats route
  participant A as authapi.geeksforgeeks.org
  participant P as practiceapi.geeksforgeeks.org

  B->>MW: GET /alice/stats
  MW->>R: GET cache:gfg:digest
  alt hit
    R-->>MW: body
    MW-->>B: 200 X-Cache HIT
  else miss
    MW->>R: GET invalid:gfg:alice
    MW->>R: INCR rl:ip and rl:handle
    MW->>RT: call_next
    RT->>A: user-profile-info
    RT->>P: problems submissions
    RT-->>MW: envelope
    MW->>R: SETEX cache 3600s
    MW-->>B: 200 X-Cache MISS
  end

IP is X-Forwarded-For first hop, else X-Real-IP, else request.client.host. Vercel sits in front, so the forwarded header is the one that matters.

/playground is not in SKIP_PATHS. With Redis on, the first path segment is treated as handle playground. Harmless, slightly weird.

Invalid-user markers: user does not exist, user not found, not found on, invalid username. Contest-empty is not one of them. Contests, rating, and badges return empty models on a real user, so those 200s are cached as normal HIT, not NEGATIVE-HIT.

REDIS_URL turns the middleware on. There is no in-process HTTP cache. Redis errors fail open: cache miss, rate limit allow.

Keys:

• cache:gfg:{sha256}
• invalid:gfg:{handle}
• rl:ip:gfg:{ip} / rl:handle:gfg:{handle}
• backoff:{same} / violations:{same}