Type Alias Headerify<T>

Headerify: {
    [P in keyof T]?: T[P] extends HeaderValue
    | undefined
        ? P extends string
            ? Lowercase<P> extends "set-cookie"
                ? T[P] extends HeaderValue[] ? T[P] | undefined : never
                : Lowercase<P> extends
                    | "age"
                    | "authorization"
                    | "content-length"
                    | "content-type"
                    | "etag"
                    | "expires"
                    | "from"
                    | "host"
                    | "if-modified-since"
                    | "if-unmodified-since"
                    | "last-modified"
                    | "location"
                    | "max-forwards"
                    | "proxy-authorization"
                    | "referer"
                    | "retry-after"
                    | "server"
                    | "user-agent"
                    ? T[P] extends HeaderValue[] ? never : T[P] | undefined
                    : T[P] | undefined
            : never
        : never
}