fasthx.component_selectors

ComponentHeader dataclass

Bases: Generic[T]

Component selector that takes the component key from a request header.

This class makes it possible for the client to submit the key/ID of the required component to the server in a header. This component selector will look up the requested component factory and return it for rendering.

If the client doesn't request a specific component, then default will be used if it was set, otherwise an exception will be raised.

By default this class treats component keys as case-insensitive. If you'd like to disable this behavior, set case_sensitive to True.

This component selector also support error rendering.

Implements

• RequestComponentSelector.

Source code in fasthx/component_selectors.py

@dataclass(frozen=True, slots=True)
class ComponentHeader(Generic[T]):
    """
    Component selector that takes the component key from a request header.

    This class makes it possible for the client to submit the *key/ID* of the required component
    to the server in a header. This component selector will look up the requested component
    factory and return it for rendering.

    If the client doesn't request a specific component, then `default` will be used if it was set,
    otherwise an exception will be raised.

    By default this class treats component keys as case-insensitive. If you'd like to disable
    this behavior, set `case_sensitive` to `True`.

    This component selector also support error rendering.

    Implements:
        - `RequestComponentSelector`.
    """

    header: str
    """The header which is used by the client to communicate the *key* of the requested component."""

    components: dict[str, T]
    """Dictionary that maps errors to component factories."""

    error: type[Exception] | tuple[type[Exception], ...] | None = field(default=None, kw_only=True)
    """The accepted error or errors."""

    default: T | None = field(default=None, kw_only=True)
    """The component factory to use if the client didn't request a specific one."""

    case_sensitive: bool = field(default=False, kw_only=True)
    """Whether the keys of `components` are case-sensitive or not (default is `False`)."""

    def __post_init__(self) -> None:
        if not self.case_sensitive:
            object.__setattr__(
                self,
                "components",
                {k.lower(): v for k, v in self.components.items()},
            )

    def get_component(self, request: Request, error: Exception | None) -> T:
        """
        Returns the component factory to use to render the response.

        If the request doesn't contain a header (with the name `self.header`),
        then `self.default` will be returned if it's not `None`.

        Raises:
            KeyError: If the client request an unknown component or if no component
                was requested and there is no default either.
        """
        if error is not None and (self.error is None or not isinstance(error, self.error)):
            raise error

        if (key := request.headers.get(self.header, None)) is not None:
            if not self.case_sensitive:
                key = key.lower()

            return self.components[key]
        elif self.default is None:
            raise KeyError("Default component factory was not set and header was not found.")
        else:
            return self.default

case_sensitive: bool = field(default=False, kw_only=True) class-attribute instance-attribute

Whether the keys of components are case-sensitive or not (default is False).

components: dict[str, T] instance-attribute

Dictionary that maps errors to component factories.

default: T | None = field(default=None, kw_only=True) class-attribute instance-attribute

The component factory to use if the client didn't request a specific one.

error: type[Exception] | tuple[type[Exception], ...] | None = field(default=None, kw_only=True) class-attribute instance-attribute

The accepted error or errors.

header: str instance-attribute

The header which is used by the client to communicate the key of the requested component.

get_component(request, error)

Returns the component factory to use to render the response.

If the request doesn't contain a header (with the name self.header), then self.default will be returned if it's not None.

Raises:

Type	Description
KeyError	If the client request an unknown component or if no component was requested and there is no default either.

Source code in fasthx/component_selectors.py

def get_component(self, request: Request, error: Exception | None) -> T:
    """
    Returns the component factory to use to render the response.

    If the request doesn't contain a header (with the name `self.header`),
    then `self.default` will be returned if it's not `None`.

    Raises:
        KeyError: If the client request an unknown component or if no component
            was requested and there is no default either.
    """
    if error is not None and (self.error is None or not isinstance(error, self.error)):
        raise error

    if (key := request.headers.get(self.header, None)) is not None:
        if not self.case_sensitive:
            key = key.lower()

        return self.components[key]
    elif self.default is None:
        raise KeyError("Default component factory was not set and header was not found.")
    else:
        return self.default