Port number changes in access logs

[jbrownkramer]

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Example Code

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def read_root():
    return {"Hello": "World"}

# Call the api once every 50 to 100 ms.

Description

I start a fastapi server on a port. I can access the server on that port, but the access logs show a changing port number for each request. What is happening there?

For example, I started a server on port 0 and it starts on port 55646. Initially accesses to this server are reported as port 55646, but eventually it starts reporting 55653. Note that I continue to access the server on port 55646.

2021-10-07 15:57:26,460 - uvicorn.access - INFO - 127.0.0.1:55646 - "GET /get_result?frame_number=5732305 HTTP/1.1" 200
2021-10-07 15:57:26,463 - uvicorn.access - INFO - 127.0.0.1:55646 - "POST /processframe_async?shape=(512,512)&dtype=uint16&frame_number=5732309 HTTP/1.1" 200
2021-10-07 15:57:39,911 - uvicorn.access - INFO - 127.0.0.1:55653 - "GET /get_result?frame_number=5732309 HTTP/1.1" 200
2021-10-07 15:57:39,917 - uvicorn.access - INFO - 127.0.0.1:55653 - "POST /processframe_async?shape=(512,512)&dtype=uint16&frame_number=5732313 HTTP/1.1" 200

I have seen situations where this port number increments on every call. Is uvicorn somehow truly using these ports? Do I have to worry about it trying to use a pre-existing port?

Operating System

Windows

Operating System Details

Windows 10.

FastAPI Version

0.65.2

Python Version

Python 3.8.10

Additional Context

No addition context.

[Kludex]

It's the client's address.

[jbrownkramer]

@Kludex Thank you!