ivcap_fastapi: Python helpers for building FastAPI based IVCAP services

A python library containing various helper and middleware functions to support converting FastAPI based tools into IVCAP services.

Content

• Try-Later Middleware
• JSON-RPC Middleware

Try-Later Middleware

This middleware is supporting the use case where the execution of a requested service is taking longer than the caller is willing to wait. A typical use case is where the service is itself outsourcing the execution to some other long-running service but may immediately receive a reference to the eventual result.

In this case, raising a TryLaterException will return with a 204 status code and additional information on how to later check back for the result.

from ivcap_fastapi import TryLaterException, use_try_later_middleware
use_try_later_middleware(app)

@app.post("/big_job")
def big_job(req: Request) -> Response:
    jobID, expected_exec_time = scheduling_big_job(req)
    raise TryLaterException(f"/jobs/{jobID}", expected_exec_time)

@app.get("/jobs/{jobID}")
def get_job(jobID: str) -> Response:
    resp = find_result_for(job_id)
    return resp

Specifically, raising TryLaterException(location, delay) will return an HTTP response with a 204 status code with the additional HTTP headers Location and Retry-Later set to location and delay respectively.

JSON-RPC Middleware

This middleware will convert any POST / with a payload following the JSON-RPC specification to an internal POST /{method} and will return the result formatted according to the JSON-RPC spec.

from ivcap_fastapi import use_json_rpc_middleware
use_json_rpc_middleware(app)