Response body info.response.body is still empty

[trallnag]

Minimal script to reproduce:

from fastapi import FastAPI
from prometheus_fastapi_instrumentator import Instrumentator, metrics

app = FastAPI()


@app.get("/ping")
def get_ping():
    return "pong" * 10000000

def instrumentation(info: metrics.Info) -> None:
    print("Length of response body: " + str(len(info.response.body)))

Instrumentator().instrument(app).add(instrumentation)

Start with uvicorn main:app and do curl localhost:8000/ping | wc -c.

Observe output. The body size is shown as zero.

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Maybe it only works if response is being streamed?

Here is example with data being streamed:

from fastapi import FastAPI, StreamingResponse
from prometheus_fastapi_instrumentator import Instrumentator, metrics

app = FastAPI()

CHUNK_SIZE = 1024 * 1024
some_file_path = 'large_file.tar'
app = FastAPI()

@app.get('/')
def main():
    def iterfile():
        with open(some_file_path, 'rb') as f:
            while chunk := f.read(CHUNK_SIZE):
                yield chunk

    headers = {'Content-Disposition': 'attachment; filename="large_file.tar"'}
    return StreamingResponse(iterfile(), headers=headers, media_type='application/x-tar')

def instrumentation(info: metrics.Info) -> None:
    print("Length of response body: " + str(len(info.response.body)))

Instrumentator().instrument(app).add(instrumentation)

Try again. Don't forget to create a largish file. 50 MB is fine. It now works.

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Related #203 and #76.