svcforge/services/api/main.py

"""The app factory and its lifespan.

`create_app(settings)` is a factory, not a module-level `app = FastAPI()`, for one reason:
a test needs an app pointed at a throwaway Postgres, and an import-time app reads the real
environment at import time — before any fixture can say otherwise.
"""

from __future__ import annotations

import asyncio
from collections.abc import AsyncIterator
from contextlib import asynccontextmanager

from fastapi import FastAPI, Request
from fastapi.exceptions import RequestValidationError
from fastapi.responses import JSONResponse
from jwt import PyJWKClient
from starlette.exceptions import HTTPException

from services.api.models import ErrorBody
from services.api.routes import health, instances
from svcforge_core import obs
from svcforge_core.adapters.redis import RateLimiter, make_redis
from svcforge_core.domain.catalog import load_catalog
from svcforge_core.repo.db import make_pool
from svcforge_core.settings import Settings, load_settings

log = obs.get_logger("svcforge.api")


@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncIterator[None]:
    """Open the pool, yield, close the pool.

    A lifespan context, not the deprecated startup/shutdown event decorators: those cannot
    express "this resource lives for exactly as long as the app", and give you no place to
    put the teardown next to the setup. Closing the pool matters — an unclosed pool means
    connections linger server-side after SIGTERM, and on a pooled Postgres with a small
    connection budget a few rolling deploys exhaust it.

    (The old decorator's name is spelled nowhere in this package on purpose: CI greps for
    the literal string, and a comment quoting it fails the gate just as loudly as a call.)
    """
    settings: Settings = app.state.settings

    app.state.catalog = load_catalog(settings.catalog_path)

    # Redis is optional by construction. `make_redis` returns None when no DSN is set, and
    # every consumer treats None as "skip" — so a deployment without Redis loses rate
    # limiting and keeps everything else. Built here rather than per request because a
    # connection pool per request is a connection pool per request.
    redis = make_redis(settings)
    app.state.redis = redis
    app.state.rate_limiter = (
        RateLimiter(redis, limit=settings.rate_limit_per_minute, window_s=60) if redis is not None else None
    )

    pool = make_pool(str(settings.pg_dsn), settings.pool_min_size, settings.pool_max_size)
    # wait=True fails NOW, loudly, if the DSN is wrong — instead of at the first request,
    # as a PoolTimeout, in front of a user.
    await pool.open(wait=True)
    app.state.pool = pool

    # The pool is open from here on, so everything below is inside the try: an exception
    # in JWKS setup must still close it, or a crash-looping pod leaks a connection per
    # restart until the database refuses new ones.
    try:
        if settings.jwks_url and not settings.auth_disabled:
            client = PyJWKClient(settings.jwks_url, cache_keys=True, lifespan=300)
            app.state.jwks_client = client
            # Warm the cache off the loop so the first authenticated request does not pay
            # a blocking urlopen. Best-effort: a slow identity provider must not stop the
            # pod from starting — a cache miss later just costs one to_thread hop.
            try:
                await asyncio.to_thread(client.get_signing_keys)
            except Exception:  # deliberate catch-all: startup must not hinge on the IdP being up
                log.warning("JWKS warm-up failed; keys will be fetched on first use", exc_info=True)
        else:
            app.state.jwks_client = None

        yield
    finally:
        await pool.close()
        if redis is not None:
            await redis.aclose()


async def _http_exception_handler(request: Request, exc: Exception) -> JSONResponse:
    """Render HTTPException bodies as ErrorBody, so every error has one shape.

    Handlers raise `detail={"code": ..., "message": ...}`; FastAPI's default would nest
    that under `{"detail": {...}}`. Plain-string details (raised by FastAPI itself, e.g.
    a 405) are wrapped so clients never have to branch on the body's type.

    Registered on starlette's HTTPException, not fastapi's. fastapi.HTTPException is a
    subclass, and Starlette matches handlers by walking type(exc).__mro__, so a handler
    keyed on the subclass never fires for a framework-raised 404 or 405 — which are
    starlette.HTTPException instances. Keying on the parent catches both: app handlers
    raise the FastAPI subclass with a dict detail, the framework raises the parent with a
    str detail, and the branch below renders each into ErrorBody.
    """
    assert isinstance(exc, HTTPException)  # noqa: S101 - registered only for HTTPException
    # Widened to object deliberately. Starlette types `detail` as str, but FastAPI passes
    # through whatever a handler raised — our handlers raise dicts. Narrowing off the
    # declared type would make mypy call the dict branch unreachable and delete it.
    detail: object = exc.detail
    if isinstance(detail, dict) and "code" in detail and "message" in detail:
        body = ErrorBody(code=str(detail["code"]), message=str(detail["message"]))
    else:
        body = ErrorBody(code=f"http_{exc.status_code}", message=str(detail))
    return JSONResponse(status_code=exc.status_code, content=body.model_dump(), headers=exc.headers)


async def _validation_exception_handler(request: Request, exc: Exception) -> JSONResponse:
    """Render request-validation failures as ErrorBody too.

    A body that fails validation (a forbidden extra field, a bad type, an out-of-range
    ttl_days) raises RequestValidationError, which the HTTPException handler above never
    sees. Without this it returns FastAPI's default `{"detail": [...]}` — a second 422 shape
    alongside the ErrorBody 422s the handlers raise. This gives every 422 one shape.
    """
    assert isinstance(exc, RequestValidationError)  # noqa: S101 - registered only for this
    return JSONResponse(
        status_code=422,
        content=ErrorBody(code="validation_error", message=str(exc.errors())).model_dump(),
    )


def create_app(settings: Settings | None = None) -> FastAPI:
    """App factory: lifespan, routers, exception handler, /metrics."""
    settings = settings or load_settings()

    # FIRST, before any router is built and before any logger is bound. Without this the
    # API is the one service of three that never configures structlog: its lines go out
    # through logging.lastResort as bare text on stderr with no service, no trace_id and
    # no JSON envelope — a parse failure in the collector, and unattributable in Loki.
    # `settings.log_json` was silently inert here for the same reason.
    obs.setup("svcforge-api", settings)

    # Refuse the dev escape hatches when SVCFORGE_ENVIRONMENT says this is not a laptop.
    # Called unconditionally and early: a check that only runs from a branch someone
    # remembered to write is a check that does not run.
    settings.check_production()

    app = FastAPI(
        title="svcforge",
        version="0.1.0",
        summary="X-as-a-Service control plane",
        lifespan=lifespan,
    )
    app.state.settings = settings

    # /metrics is a normal route on health.router, not an app.mount — see health.metrics
    # for why the mount does not actually serve a bare /metrics.
    app.include_router(health.router)
    app.include_router(instances.router)

    app.add_exception_handler(HTTPException, _http_exception_handler)
    app.add_exception_handler(RequestValidationError, _validation_exception_handler)
    return app


def app() -> FastAPI:
    """Entry point for `uvicorn services.api.main:app --factory`."""
    return create_app()


# There is deliberately no `if __name__ == "__main__"` here. `services/api/__main__.py` is
# the single entrypoint, and the image's ENTRYPOINT uses it. A second one in this module
# drifted from it — different log_level, different access_log — so `python -m services.api`
# and `python services/api/main.py` started the same app two different ways.