How can I return a 202 Accepted response for long running REST call?

Hope this is the right place for a question.

I have a REST API post request that does a lot of computation, /crunch. Rather than block the event loop I would like /crunch to return 202 Accepted status code along with a token string. Then the user of the API can call get request /result/{token} to check on the status of the computation. This is outlined nicely here for example.

Is it possible to modify the response status code, for example, similar to this approach in Sanic?

[tiangolo]

@danieljfarrell here’s a bit of history, now in the docs: https://fastapi.tiangolo.com/history-design-future/

And I quoted you 😁

[rcox771]

@danieljfarrell Its really easy to modify the response code to suit your needs. In the example below, I use /jobs to post new jobs to. This returns a HTTP_201_CREATED on submit. You can then take the id that it generates and call GET /jobs/{id} to check the status, along with its HTTP_202_ACCEPTED code 🎉. Note: I’m using deque’s because they’re thread-safe, but I haven’t thoroughly tested this out and haven’t implemented task switching/moving jobs around to different queues. Hope it helps!

from fastapi import FastAPI
from pydantic import BaseModel
from uuid import uuid4
from collections import deque
from starlette.status import HTTP_201_CREATED, HTTP_202_ACCEPTED
# see https://github.com/encode/starlette/blob/master/starlette/status.py

queues = dict(
    pending=deque(),
    working=deque(),
    finished=deque()
)

def get_job(id: str, queue: str = None, order=['finished', 'working', 'pending']):
    _id = str(id)
    # if queue:
    #    order = [queue]
    for queue in order:
        for job in queues[queue]:
            # print(job['id'])
            if str(job['id']) == _id:
                return job, queue
    return 'not found', None #this will fail horribly


app = FastAPI()

class BaseJob(BaseModel):
    data: bytes = None

class JobStatus(BaseModel):
    status: str
    id: str
    data: bytes = None
    result: int = -1


@app.get("/jobs/{id}", response_model=JobStatus, status_code=HTTP_202_ACCEPTED)
async def read_job(id: str):
    job, status = get_job(id)
    d = dict(
        id=job['id'],
        status=status,
        data=job['data'],
        result=job.get('result', -1)
    )
    return d

@app.post("/jobs/", response_model=JobStatus, status_code=HTTP_201_CREATED)
async def create_job(*, job: BaseJob):
    _job = dict(
        id=str(uuid4()),
        status='pending',
        data=job.data
    )
    queues['pending'].append(_job)
    return _job

Submitting a new job, getting its id

Getting the status for a job, given its id