How to forward headers using FastAPI - Tracing use cases

Question

Below is simple server written with FastAPI and running with Uvicorn.

In order to send the value to the next hop, the '/destination' url, I need to pass the value to the forward_request method.

In this implementation, passing the value is easy, because the calls' depth is just 1 function more.

But if I have a function that calls a function that calls a function...., I need to pass the value again and again and...

Is there a simpler way to share the value downstream without passing it?

Is there a way, without using inspect or some dark magic, to understand what is the scope that the function forward_request lives in?

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Why am I asking this question?

I am using Jaeger for tracing and I need to forward the header x-request-id that I receive in the 1st server (/source in this example) to the 2nd server (/destination in this example).

If FastAPI\Uvicorn processed just 1 request at a time, I could have shared the value as a singleton class and access it from anywhere, but since requests are handled in parallel, the function forward_request doesn't have the context of who called it.

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Some black magic

Function forward_request can inspect the call stack and figure from it, what is the value that was received, but that is one ugly way to do things.

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Server Code

import asyncio

import aiohttp as aiohttp
from fastapi import FastAPI, Request
import uvicorn

from datetime import datetime

app = FastAPI()


@app.get("/source")
async def route1(value: int, request: Request):
    print(f'source {value}')
    start = datetime.now().strftime("%H:%M:%S")
    await asyncio.sleep(5)
    resp: dict = await forward_request(value)
    end = datetime.now().strftime("%H:%M:%S")
    return {
        "start": start,
        "end": end,
        "value": value,
        "resp": resp
    }


@app.get("/destination")
async def route2(value, request: Request):
    print(f'destination {value}')
    start = datetime.now().strftime("%H:%M:%S")
    await asyncio.sleep(5)
    end = datetime.now().strftime("%H:%M:%S")
    return {
        "start": start,
        "end": end,
        "value": value
    }


async def forward_request(value: int) -> dict:
    async with aiohttp.ClientSession() as session:
        async with session.get('http://127.0.0.1:5000/destination', params={'value': value}) as resp:
            resp = await resp.json()

    return resp


if __name__ == "__main__":
    uvicorn.run("main2:app", host="127.0.0.1", port=5000, log_level="info", workers=1)