wyolet-primitives

Stateful ASGI primitives — rate limit, distributed lock, idempotency, session, user-session, cache, dedup, circuit breaker, feature flags, OTP — sharing one pluggable Backend. Memory, SQLite, Redis, Valkey, Postgres.

First package under the wyolet namespace.

uv add wyolet-primitives                 # core (memory backend)
uv add "wyolet-primitives[sqlite]"       # + SQLiteBackend
uv add "wyolet-primitives[redis]"        # + RedisBackend
uv add "wyolet-primitives[valkey]"       # + ValkeyBackend
uv add "wyolet-primitives[postgres]"     # + PostgresBackend + PostgresUserSessionRepo
uv add "wyolet-primitives[cache]"        # + orjson JSON serializer

Why

FastAPI projects keep reinventing the same primitives. Existing packages are each scoped to one — slowapi for rate limiting, redlock-py for locks, cashews for caching — each with its own storage abstraction, lifecycle, and framework coupling. wyolet.primitives unifies them: implement one Backend, get every primitive that needs state. All middlewares are pure ASGI — FastAPI, Starlette, Litestar, BlackSheep, Quart all work.

Primitives

Module	What	Needs
ratelimit	FixedWindow strategy + ASGI middleware with key extractors (IP, header, cookie, scope) and standard X-RateLimit-* headers.	any Backend
lock	DistributedLock with TTL, fencing-safe release (compare-and-delete), optional auto-renew.	any Backend
idempotency	Idempotency-Key header middleware. Caches original response, serializes concurrent replays via lock, never caches 5xx.	any Backend
session	Ephemeral cookie-session. Flat payload, dirty-tracking, regenerate() for fixation defense, pure-ASGI signed-cookie middleware.	any Backend
user_session	Device/login records (user_id, ua, ip, os, device, …). Pluggable repo + cache-aside wrapper + service. Ship-your-own schema via pydantic subclassing.	UserSessionRepo impl (Postgres shipped)
cache	Cache class + @cached decorator with stampede protection via lock. HTTPCacheMiddleware for response-level caching (honors Cache-Control, explicit Vary). Pluggable serializers (PickleSerializer, JSONSerializer via orjson).	any Backend
dedup	claim() / once() — atomic "have I seen this ID?" for webhook receivers, queue consumers, cron-once-across-replicas.	any Backend
circuit_breaker	Stateless per-process breaker. Three states (closed/open/half-open) with single-probe recovery. Decorator, context-manager, and .call(fn) forms.	—
feature_flags	Booleans + percentage rollout + allow/block lists with in-process TTL cache. Deterministic per-subject bucketing, salted by flag name.	any Backend
otp	Issue / verify single-use codes. Hashed storage, constant-time compare, attempt limits, resend cooldown.	any Backend

Backends

	TTL	Locks	Incr	Notes
MemoryBackend	✔	✔	✔	asyncio-safe, monotonic-clock TTL, lazy eviction + sweep. Dev / test / single-process.
SQLiteBackend	✔	✔	✔	via aiosqlite. WAL mode, single-connection + lock. For single-node deploys and local dev without docker.
RedisBackend	✔	✔	✔	over redis.asyncio.Redis. Tiny Lua script for compare-and-delete.
ValkeyBackend	✔	✔	✔	over valkey.asyncio.Valkey. Drop-in for Redis.
PostgresBackend	✔	✔	✔	over psycopg_pool.AsyncConnectionPool. TIMESTAMPTZ server-clock TTL, upsert-based set_nx / incr. For teams with Postgres but no Redis.

Bring-your-own: subclass wyolet.primitives.backends.base.Backend (ABC), implement get / set / delete / incr / expire / set_nx / compare_and_delete. Every primitive works on it.

Quickstart — FastAPI

from fastapi import FastAPI
from redis.asyncio import Redis

from wyolet.primitives.backends.redis import RedisBackend
from wyolet.primitives.session import SessionMiddleware
from wyolet.primitives.ratelimit import FixedWindow, RateLimitMiddleware, compose, from_scope, from_ip
from wyolet.primitives.idempotency import IdempotencyMiddleware

backend = RedisBackend(Redis.from_url("redis://localhost"))
app = FastAPI()

# Rate limit: prefer user_id if upstream middleware set it, else client IP
app.add_middleware(
    RateLimitMiddleware,
    strategy=FixedWindow(backend, limit=100, window=60),
    key=compose(from_scope("user_id"), from_ip()),
)

# Idempotent POST/PUT/PATCH/DELETE on `Idempotency-Key` header
app.add_middleware(IdempotencyMiddleware, backend=backend, ttl=86400)

# Signed-cookie session
app.add_middleware(
    SessionMiddleware,
    backend=backend,
    secret_key="change-me",
    cookie_name="sid",
    max_age=14 * 24 * 3600,
)

@app.post("/orders")
async def create_order(request):
    session = request.scope["session"]
    session["last_order"] = "ord-123"  # auto-saved at response
    ...

Distributed lock

from wyolet.primitives.lock import DistributedLock, LockAcquireError

lock = DistributedLock(backend, ttl=30, wait=5.0)

async with lock.acquire(f"order:{order_id}"):
    await process_order(order_id)  # auto-renewed while this runs

Fencing is handled for you: if the TTL expires and another holder takes over, the original holder's release() returns False without deleting the new holder's key.

Cache

from wyolet.primitives.cache import Cache, cached, HTTPCacheMiddleware

cache = Cache(backend, ttl=300)

@cached(cache, ttl=60)
async def get_user(user_id: str) -> dict:
    return await db.fetch_one(...)  # 1000 concurrent misses → 1 DB call

# Or response-level caching:
app.add_middleware(HTTPCacheMiddleware, backend=backend, ttl=60, vary=("accept-encoding",))

Dedup

from wyolet.primitives.dedup import Dedup

dedup = Dedup(backend, ttl=3 * 24 * 3600)  # Stripe retries for 3 days

@app.post("/webhook/stripe")
async def stripe_webhook(event: dict):
    async with dedup.once(f"stripe:{event['id']}") as first:
        if not first:
            return {"status": "duplicate"}
        await process(event)  # rolled back on exception
        return {"status": "ok"}

Circuit breaker

from wyolet.primitives.circuit_breaker import CircuitBreaker, CircuitOpenError

stripe_breaker = CircuitBreaker(fail_threshold=5, recovery_timeout=30)

@stripe_breaker.guard
async def charge(amount: int):
    return await stripe.charge(amount)

try:
    await charge(1000)
except CircuitOpenError:
    return {"error": "payment provider unavailable"}  # fail fast, don't pile on

Feature flags

from wyolet.primitives.feature_flags import FeatureFlags

flags = FeatureFlags(backend, cache_ttl=10.0)

# Admin:
await flags.set("new_checkout", enabled=True, rollout=25, allow=["beta-user-1"])

# Hot path:
if await flags.is_enabled("new_checkout", subject=user.id):
    return new_flow()
return old_flow()

Bucketing identity is caller-chosen: user.id for logged-in features, session.id for pre-login A/B, org.id for B2B per-tenant rollout.

OTP

from wyolet.primitives.otp import Otp, OtpNotFoundError, OtpTooManyAttemptsError

otp = Otp(backend, ttl=300, code_length=6, max_attempts=5, resend_cooldown=30)

code = await otp.issue(phone_number)
await sms.send(phone_number, f"Your code is {code}")

# Verification endpoint:
try:
    ok = await otp.verify(phone_number, submitted_code)
except OtpNotFoundError:
    return {"error": "code expired or never sent"}
except OtpTooManyAttemptsError:
    return {"error": "too many attempts, request a new code"}
return {"ok": ok}

User sessions (devices logged in)

from psycopg_pool import AsyncConnectionPool

from wyolet.primitives.user_session import CachedUserSessionRepo, UserSession, UserSessionService
from wyolet.primitives.user_session.postgres import PostgresUserSessionRepo

pool = AsyncConnectionPool("postgresql://...")
pg_repo = PostgresUserSessionRepo(pool, model=UserSession)
await pg_repo.ensure_schema()

repo = CachedUserSessionRepo(pg_repo, backend, model=UserSession, ttl=3600)
service = UserSessionService(repo, model=UserSession)

# On login:
session = await service.create(
    user_id=user.id, user_agent=ua, ip=request.client.host, os="macOS", device="Desktop",
)

# Devices-logged-in UI:
devices = await service.list_active(user.id)

# Revoke remotely:
await service.revoke(some_sid)

Extend by subclassing:

class MyUserSession(UserSession):
    tenant_id: str
    last_location: str | None = None

Pass model=MyUserSession everywhere; extras live in JSONB extra column unless you also override PostgresUserSessionRepo._row_to_model / _model_to_row.

Lifecycle (FastAPI lifespan)

No separate pool/health composer — just use the stdlib pattern:

from contextlib import asynccontextmanager

@asynccontextmanager
async def lifespan(app):
    async with redis_client, pg_pool:
        await backend.start()  # for Memory/SQLite/Postgres (no-op for Redis/Valkey)
        yield
        await backend.close()

app = FastAPI(lifespan=lifespan)

Running tests

uv run pytest                      # unit tests, MemoryBackend + SQLiteBackend
docker compose up -d               # redis/valkey/postgres for the rest
uv run pytest                      # parametrized backend tests now hit all five
uv run pytest -m integration       # live-service tests (user_session postgres)

Deliberately out of scope

• Retry / backoff — use tenacity or stamina. Stateless; no backend unification story.
• Pool composer / health composer — each async lib ships its own pool. Stdlib @asynccontextmanager is a 5-line solution.
• WebSockets — FastAPI native is enough.
• ORM / DB layer — sqlmodel / sqlalchemy own this.
• Background task queues — use taskiq / arq.

Roadmap

v0.1 (shipped): ratelimit (FixedWindow), lock, idempotency, session, user_session, cache (+ HTTPCache), dedup, circuit_breaker, feature_flags, otp; Memory/SQLite/Redis/Valkey/Postgres backends.

Next: more rate-limit strategies (token bucket, sliding window) via ScriptableBackend / LockableBackend capability mixins.

License

TBD.