Returning a Pillow image that only exists in memory

[Vuizur]

I have a program that programmatically creates an image using Pillow. I want to return it using Starlite. I tried combining a bit FastAPI-inspired code from Stackoverflow + following the docs a bit, but couldn't get it to work.

@get(
    "randompic/{lang:str}",
    media_type='image/jpeg'
)
def randompic(lang: str) -> io.BytesIO:
    img = rdpgen.generate_random_definition_pic(lang)
    # return img as bytes
    buf = io.BytesIO()
    img.save(buf, format="JPEG")
    buf.seek(0)

    return Response(content=buf, media_type="image/jpeg")

If you send a request, then you get the response {"status_code":500,"detail":"Unable to serialize response content"}. What would be the best way to achieve this?

[Goldziher]

Have you tried using a streaming response: https://starlite-api.github.io/starlite/1.48/usage/5-responses/8-streaming-responses/

[provinzkraut]

Two things:

1. Your return annotation is incorrect. You are not returning io.BytesIO but a Response
2. If you want to send a "raw" response, you should provide bytes, not io.BytesIO.

Therefore, the fix looks like this:

@get(
    "randompic/{lang:str}",
    media_type='image/jpeg'
)
def randompic(lang: str) -> Response[bytes]:
    img = rdpgen.generate_random_definition_pic(lang)
    # return img as bytes
    buf = io.BytesIO()
    img.save(buf, format="JPEG")
    buf.seek(0)

    return Response(content=buf.read(), media_type="image/jpeg")

Alternatively you could do what @Goldziher suggested and stream the file from memory, which depending on its size might be an advantage or a disadvantage.

[Vuizur]

Thank you a lot, this works flawlessly!