105 lines
3.5 KiB
Python
105 lines
3.5 KiB
Python
"""
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OpenAPI-first application bootstrap for FastAPI.
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---
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## Summary
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This module provides `OpenAPIFirstApp`, a thin but strict abstraction
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that enforces OpenAPI as the single source of truth for a FastAPI service.
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Notes:
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**Core Principles:**
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- The OpenAPI specification (JSON or YAML) defines the entire API surface
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- Every operationId in the OpenAPI spec must have a corresponding Python handler function
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- Handlers are plain Python callables (no FastAPI decorators)
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- FastAPI route registration is derived exclusively from the spec
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- FastAPI's autogenerated OpenAPI schema is fully overridden
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**Responsibilities:**
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- Loads and validates an OpenAPI 3.x specification
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- Dynamically binds HTTP routes to handler functions using operationId
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- Registers routes with FastAPI at application startup
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- Ensures runtime behavior matches the OpenAPI contract exactly
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**Constraints:**
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- This module intentionally does NOT: Generate OpenAPI specs, generate client code, introduce a new framework or lifecycle, or alter FastAPI dependency injection semantics.
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"""
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from fastapi import FastAPI
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from .loader import load_openapi
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from .binder import bind_routes
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class OpenAPIFirstApp(FastAPI):
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"""
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FastAPI application enforcing OpenAPI-first design.
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Notes:
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**Responsibilities:**
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- `OpenAPIFirstApp` subclasses FastAPI and replaces manual route registration with OpenAPI-driven binding
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- All routes are derived from the provided OpenAPI specification, and each operationId is mapped to a Python function in the supplied routes module
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**Guarantees:**
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- No route can exist without an OpenAPI declaration
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- No OpenAPI operation can exist without a handler
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- Swagger UI and `/openapi.json` always reflect the provided spec
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- Handler functions remain framework-agnostic and testable
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Example:
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```python
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from openapi_first import OpenAPIFirstApp
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import app.routes as routes
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app = OpenAPIFirstApp(
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openapi_path="app/openapi.json",
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routes_module=routes,
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title="Example Service",
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)
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```
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"""
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def __init__(
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self,
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*,
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openapi_path: str,
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routes_module,
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**fastapi_kwargs,
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):
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"""
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Initialize the application.
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Args:
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openapi_path (str):
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Filesystem path to the OpenAPI 3.x specification file. This specification is treated as the authoritative API contract.
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routes_module (module):
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Python module containing handler functions whose names correspond exactly to OpenAPI operationId values.
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**fastapi_kwargs (Any):
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Additional keyword arguments passed directly to `fastapi.FastAPI` (e.g., title, version, middleware, lifespan handlers).
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Raises:
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OpenAPIFirstError:
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If the OpenAPI specification is invalid, or if any declared operationId does not have a corresponding handler function.
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"""
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# Initialize FastAPI normally
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super().__init__(**fastapi_kwargs)
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# Load and validate OpenAPI specification
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self._openapi_spec = load_openapi(openapi_path)
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# Bind routes strictly from OpenAPI spec
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bind_routes(
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app=self,
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spec=self._openapi_spec,
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routes_module=routes_module,
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)
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# Override FastAPI's OpenAPI generation
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self.openapi = lambda: self._openapi_spec
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