How to change the client's hostname within the FastAPI's TestClient?

Question

Within my code I take the IP-address from client.host in the request object and send this to another function. There I'm using the IPvAnyAddress from Pydantic to validate if it is a valid IP-address.

Here is my code:

from fastapi import APIRouter, Request
from pydantic import IPvAnyAddress


route = APIRouter()


@route.get("/ip-address")
def request_ip_address_deblock_link(request: Request):
    return example_function(request.client.host)

def example_function(ip_address: IPvAnyAddress):
    print(ip_address)

But when I'm using FastAPI's TestClient to test my API routes, the IP-address check fails, as the hostname in the request is testclient .

ValueError: 'testclient' does not appear to be an IPv4 or IPv6 address

Is it possible to change this hostname of FastAPI's TestClient ?

Answer 1

From Starlette's source code on testclient.py here (that FastAPI actually uses under the hood, see here ), the testclient hostname seems to be fixed/hardcoded.

Hence, you could simply check on server side if request.client.host == 'testclient' inside a Dependency function (as @MatsLindh suggested in the comments section), and then, either ovveride testclient with the local IP address (if you are testing this locally), or raise some exception .

Alternatively, you could use the HTTPX library, also suggested in the FastAPI documentation . FastAPI/ Starlette 's TestClient is now built on httpx (see the relevant commit on github ).