Vishesh 'ironeagle' Bangotra
2f444a93ad
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119 lines
3.6 KiB
Python
119 lines
3.6 KiB
Python
"""
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openapi_first.app
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=========================
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OpenAPI-first application bootstrap for FastAPI.
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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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Core principles
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---------------
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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
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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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What this module does
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---------------------
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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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What this module does NOT do
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----------------------------
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- It does not generate OpenAPI specs.
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- It does not generate client code.
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- It does not introduce a new framework or lifecycle.
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- It does not alter FastAPI dependency injection semantics.
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Intended usage
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--------------
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This module is intended for teams that want:
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- OpenAPI-first API development
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- Strong contract enforcement
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- Minimal FastAPI boilerplate
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- Predictable, CI-friendly failures for spec/implementation drift
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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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`OpenAPIFirstApp` subclasses FastAPI and replaces manual route
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registration with OpenAPI-driven binding. All routes are derived
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from the provided OpenAPI specification, and each operationId is
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mapped to a Python function in the supplied routes module.
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Parameters
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----------
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openapi_path : str
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Filesystem path to the OpenAPI 3.x specification file.
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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
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exactly to OpenAPI operationId values.
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**fastapi_kwargs
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Additional keyword arguments passed directly to `fastapi.FastAPI`
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(e.g., title, version, middleware, lifespan handlers).
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Raises
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------
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OpenAPIFirstError
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If the OpenAPI specification is invalid, or if any declared
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operationId does not have a corresponding handler function.
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Behavior guarantees
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-------------------
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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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-------
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>>> from openapi_first import OpenAPIFirstApp
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>>> import app.routes as routes
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>>>
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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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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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# 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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