Error in handling duplicate query parameters

[yhl-cs]

Describe the Bug

When sending an HTTP request with multiple query parameters of the same name (e.g., command=ls&command=-l&command=--full-time&command=/), the parameters are incorrectly processed after passing through a reverse proxy.
Specifically, the proxy merges or drops duplicate parameters, resulting in the backend server receiving malformed parameters (e.g., only command=/).

This issue also affects WebSocket requests.

To Reproduce

1. Run the server:

# http-server.py
from fastapi import FastAPI, Request

app = FastAPI()

@app.get("/test")
async def handle_request(request: Request):
    return {
        "message": "Request received by server",
        "query_params": request.query_params.__dict__,
    }

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="127.0.0.1", port=8766)

$ python http-server.py 
INFO:     Started server process [1097915]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8766 (Press CTRL+C to quit)

2. Run the reverse proxy:

# http_rs.py
from fastapi_proxy_lib.fastapi.app import reverse_http_app

app = reverse_http_app(base_url="http://127.0.0.1:8766/")

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=8765)

$ python ./http-rs.py 
INFO:     Started server process [1098305]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8765 (Press CTRL+C to quit)

3. Send the HTTP request:

$ curl "http://127.0.0.1:8765/test?stdin=false&stdout=true&command=ls&command=-l&command=--full-time&command=%2F"
{"message":"Request received by server","query_params":{"_dict":{"stdin":"false","stdout":"true","command":"/"},"_list":[["stdin","false"],["stdout","true"],["command","/"]]}}

4. Check the reverse proxy status (receives correct query parameters):

$ python ./http-rs.py 
INFO:     Started server process [1098305]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8765 (Press CTRL+C to quit)
INFO:     127.0.0.1:33962 - "GET /test?stdin=false&stdout=true&command=ls&command=-l&command=--full-time&command=%2F HTTP/1.1" 200 OK

5. Check the server status (receives incorrect query parameters):

$ python http-server.py 
INFO:     Started server process [1097915]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://127.0.0.1:8766 (Press CTRL+C to quit)
INFO:     127.0.0.1:48436 - "GET /test?stdin=false&stdout=true&command=%2F HTTP/1.1" 200 OK

Expected Behavior

The query parameters should remain unchanged after passing through the reverse proxy. For example:

INFO:     127.0.0.1:58978 - "GET /test?stdin=false&stdout=true&stderr=true&tty=false&command=ls&command=-l&command=--full-time&command=%2F HTTP/1.1" 200 OK

Additional Context

The original request query parameters are stdin=false&stdout=true&command=ls&command=-l&command=--full-time&command=%2F. These are converted into starlette.datastructures.QueryParams ¹:

{'_dict': {'stdin': 'command': '/'}, '_list': [('stdin', 'false'), ('stdout', 'true'), ('command', 'ls'), ('command', '-l'), ('command', '--full-time'), ('command', '/')]}

During the initialization of httpx.QueryParams, the code enters the else branch ². Here, value.items() only iterates over value._dict, resulting in the final httpx.QueryParams data:

{'stdin': ['false'], ('stdout', 'true'), 'command': ['/']}

Theoretically, it should iterate over value._list instead.

Configuration

• python 3.12.3
• httpx 0.28.1
• fastAPI 0.115.6
• fastAPI-proxy-lib 0.2.0

Footnotes

1. https://github.com/encode/starlette/blob/master/starlette/datastructures.py#L373 ↩

2. https://github.com/encode/httpx/blob/master/httpx/_urls.py#L436 ↩

[WSH032]

@yhl-cs Nice catch! I think we just need to change these two pieces of code to request.query_params.multi_items():

• fastapi-proxy-lib/src/fastapi_proxy_lib/core/http.py

  Line 270 in 64a7be4

  params=request.query_params,

• fastapi-proxy-lib/src/fastapi_proxy_lib/core/websocket.py

  Line 496 in 64a7be4

  client_request_params: "QueryParamTypes" = websocket.query_params

Would you like to submit a PR? 🤓