What is the best way to validate multiple headers

[poul1x]

Problem

I decided to implement api versioning using header values: api-version (trunk changes), resource-version (leaf changes).

I want to:

1. Ensure these two values are present in headers
2. Ensure these two values have int type
3. Use dependency injection to pass api version to endpoint

# Validation
class ApiVersionInfo(BaseModel):
    api_version: int
    resource_version: int

# Add dependency to app / router
def set_api_version_info(request: Request, api_ver: ApiVersionInfo = Header(...)):
    request.state.api_info = api_info

# Add dependency to endpoint
def get_api_version_info(request: Request):
    return request.state.api_info

But FastAPI does not allow to do this:

AssertionError: Param: api_info can only be a request body, using Body(...)

I've read https://fastapi.tiangolo.com/tutorial/header-params/.
But there's no common mechanism for checking and validation (like Query, Body, e.t.c).

Question: what is the best way to validate multiple headers?

[falkben]

If you specify the Header arguments individually in your dependency, you will get the validation that you want without having to create a pydantic model. In this situation, that is how I would I would go about it.

Your dependency would look like this:

def set_api_version_info(
    request: Request, api_version: int = Header(...),  resource_version: int = Header(...)
):
    request.state.api_info = api_version

And then just use that as a dependency wherever you want it. It will do the validation you want.

If you're dead set on using a pydantic model, you need to overwrite the signature of the model to convert them to Headers. A full example below, modeled after @Mause's excellent answer here about pydantic-> form: #1989 (comment)

from fastapi import Depends, FastAPI, Header, Request
from pydantic import BaseModel


def as_header(cls):
    """decorator for pydantic model
    replaces the Signature of the parameters of the pydantic model with `Header`
    """
    cls.__signature__ = cls.__signature__.replace(
        parameters=[
            arg.replace(
                default=Header(...) if arg.default is arg.empty else Header(arg.default)
            )
            for arg in cls.__signature__.parameters.values()
        ]
    )
    return cls


@as_header
class ApiVersionInfo(BaseModel):
    api_version: int
    resource_version: int


def set_api_version_info(
    request: Request, api_ver: ApiVersionInfo = Depends(ApiVersionInfo)
):
    request.state.api_info = api_ver.api_version


app = FastAPI(dependencies=[Depends(set_api_version_info)])


@app.get("/")
def get_api_version_info(request: Request):
    return request.state.api_info

[poul1x]

If you specify the Header arguments individually in your dependency, you will get the validation that you want without having to create a pydantic model.

@falkben, that's good solution, thanks!

[tiangolo]

Thanks for the help here @falkben ! 👏 🙇

Thanks for reporting back and closing the issue @poul1x 👍

Sorry for the long delay! 🙈 I wanted to personally address each issue/PR and they piled up through time, but now I'm checking each one in order.