Merge pull request #225 from lsst-sqre/tickets/DM-38339

DM-38339: Refactor mobu state management

src/mobu/dependencies/context.py

@@ -0,0 +1,86 @@
+"""Request context dependency for FastAPI.
+
+This dependency gathers a variety of information into a single object for the
+convenience of writing request handlers.  It also provides a place to store a
+`structlog.BoundLogger` that can gather additional context during processing,
+including from dependencies.
+"""
+
+from dataclasses import dataclass
+from typing import Optional
+
+from fastapi import Depends, Request
+from safir.dependencies.gafaelfawr import auth_logger_dependency
+from structlog.stdlib import BoundLogger
+
+from ..factory import ProcessContext
+from ..services.manager import FlockManager
+
+__all__ = [
+    "ContextDependency",
+    "RequestContext",
+    "context_dependency",
+]
+
+
+@dataclass(slots=True)
+class RequestContext:
+    """Holds the incoming request and its surrounding context."""
+
+    request: Request
+    """Incoming request."""
+
+    logger: BoundLogger
+    """Request loger, rebound with discovered context."""
+
+    manager: FlockManager
+    """Global singleton flock manager."""
+
+
+class ContextDependency:
+    """Provide a per-request context as a FastAPI dependency.
+
+    Each request gets a `RequestContext`.  To save overhead, the portions of
+    the context that are shared by all requests are collected into the single
+    process-global `~mobu.factory.ProcessContext` and reused with each
+    request.
+    """
+
+    def __init__(self) -> None:
+        self._process_context: Optional[ProcessContext] = None
+
+    async def __call__(
+        self,
+        request: Request,
+        logger: BoundLogger = Depends(auth_logger_dependency),
+    ) -> RequestContext:
+        """Create a per-request context."""
+        if not self._process_context:
+            raise RuntimeError("ContextDependency not initialized")
+        return RequestContext(
+            request=request,
+            logger=logger,
+            manager=self._process_context.manager,
+        )
+
+    @property
+    def process_context(self) -> ProcessContext:
+        if not self._process_context:
+            raise RuntimeError("ContextDependency not initialized")
+        return self._process_context
+
+    async def initialize(self) -> None:
+        """Initialize the process-wide shared context."""
+        if self._process_context:
+            await self._process_context.aclose()
+        self._process_context = ProcessContext()
+
+    async def aclose(self) -> None:
+        """Clean up the per-process configuration."""
+        if self._process_context:
+            await self._process_context.aclose()
+        self._process_context = None
+
+
+context_dependency = ContextDependency()
+"""The dependency that will return the per-request context."""

src/mobu/factory.py

@@ -0,0 +1,74 @@
+"""Component factory and process-wide status for mobu."""
+
+from __future__ import annotations
+
+from typing import Optional
+
+import structlog
+from aiohttp import ClientSession
+from safir.slack.webhook import SlackWebhookClient
+from structlog import BoundLogger
+
+from .config import config
+from .services.manager import FlockManager
+
+__all__ = ["Factory", "ProcessContext"]
+
+
+class ProcessContext:
+    """Per-process application context.
+
+    This object caches all of the per-process singletons that can be reused
+    for every request.
+
+    Attributes
+    ----------
+    manager
+        Manager for all running flocks.
+    session
+        Shared HTTP client session.
+    """
+
+    def __init__(self) -> None:
+        self.session = ClientSession()
+        self.manager = FlockManager(self.session, structlog.get_logger("mobu"))
+
+    async def aclose(self) -> None:
+        """Clean up a process context.
+
+        Called before shutdown to free resources.
+        """
+        await self.manager.aclose()
+        await self.session.close()
+
+
+class Factory:
+    """Component factory for mobu.
+
+    Uses the contents of a `ProcessContext` to construct the components of an
+    application on demand.
+
+    Parameters
+    ----------
+    context
+        Shared process context.
+    """
+
+    def __init__(
+        self, context: ProcessContext, logger: Optional[BoundLogger] = None
+    ) -> None:
+        self._context = context
+        self._logger = logger if logger else structlog.get_logger("mobu")
+
+    def create_slack_webhook_client(self) -> SlackWebhookClient | None:
+        """Create a Slack webhook client if configured for Slack alerting.
+
+        Returns
+        -------
+        SlackWebhookClient or None
+            Newly-created Slack client, or `None` if Slack alerting is not
+            configured.
+        """
+        if not config.alert_hook or config.alert_hook == "None":
+            return None
+        return SlackWebhookClient(config.alert_hook, "Mobu", self._logger)