Return raw bytes from endpoint function and preprocess it before send

[Redict]

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Example Code

from fastapi import FastApi

class RawResponse(Response):
    media_type = "binary/octet-stream"
     
    def render(self, content: bytes) -> bytes:
        self.body = bytes([b ^ 0x54 for b in content])

app = FastApi(default_response_class=RawResponse)

@app.get("/")
def endpoint_fn(_: Request):
    return b"\xf6j,\x90\xae\\\xf3\xd3\xaa"

Description

For this code I get 'utf-8' codec can't decode byte at routing.py:234 (serialize_response call). How can I override this?
Only one hackish solution that I've found is to b64encode(bytes) and in RawResponse render b64decode(content) then xor it

Operating System

Windows

Operating System Details

No response

FastAPI Version

0.68.1

Python Version

Python 3.9.2

Additional Context

No response

[ThirVondukr]

You can return Response (or RawResponse) object directly so fastapi doesn't try to serialize it:

class RawResponse(Response):
    media_type = "binary/octet-stream"

    def render(self, content: bytes) -> bytes:
        return bytes([b ^ 0x54 for b in content])

app = FastAPI()

@app.get("/test")
async def test():
    return RawResponse(content=b"\xf6j,\x90\xae\\\xf3\xd3\xaa")

[Redict]

You can return Response (or RawResponse) object directly so fastapi doesn't try to serialize it:

class RawResponse(Response):
    media_type = "binary/octet-stream"

    def render(self, content: bytes) -> bytes:
        return bytes([b ^ 0x54 for b in content])

app = FastAPI()

@app.get("/test")
async def test():
    return RawResponse(content=b"\xf6j,\x90\xae\\\xf3\xd3\xaa")

I need to use this in a hundred endpoints, so it doesn't work for me because it's too redundant

[ThirVondukr]

I came up with this solution that wraps endpoint function to return RawResponse automatically.
I think it's worth to leave this issue open since someone might have a better solution, and I personally don't really my solution that much 🤔

def wrap_response(endpoint: Any, response_cls: type[Response]) -> Any:
    @functools.wraps(endpoint)
    async def wrapper(*args, **kwargs):
        response = await endpoint(*args, **kwargs)
        return response_cls(content=response)

    return wrapper


class RawResponse(Response):
    media_type = "binary/octet-stream"

    def render(self, content: bytes) -> bytes:
        return bytes([b ^ 0x54 for b in content])


class RawRoute(APIRoute):
    def get_route_handler(self) -> Callable:
        self.dependant.call = wrap_response(endpoint=self.dependant.call, response_cls=RawResponse)
        return super().get_route_handler()

[TheJumpyWizard]

Any luck with implementing the above? @Redict

[Redict]

Any luck with implementing the above? @Redict

To implement that in a better way I need to go deep inside FastAPI, I don't really have time for that

[ThirVondukr]

Any luck with implementing the above? @Redict

Yep, it works, but I wonder if there's a better way of doing that, so maybe someone else would get to this issue too

[yinziyan1206]

same kwargs in apirouter

[ThirVondukr]

@yinziyan1206 That doesn't solve the problem really 🤔
Main issue is that fastapi tries to decode bytes with utf-8 encoding before creating response class

[yinziyan1206]

Oops. you just return bytes and json_encoder use lambda o: o.decode() for bytes. Maybe you should change the default encoding type or overwrite the ENCODERS_BY_TYPE in pydantic, but i suggest decode it by yourself

[ThirVondukr]

They need to return binary data, and overriding pydantic internals doesn't seem like a good idea 👀
So using decorator or something similar seems like the best way of doing that

[ShaneZhengNZ]

@ThirVondukr I tried you solution, didn't work for me. lol.

Any updates for this?

[trim21]

looks like this is by design, you will have to wrap your handler.