# Functions
BookIdPathParam extracts the 'id' parameter from the path of an HTTP request and converts it to an integer.
Param retrieves a path parameter from the URL of an HTTP request.
RespondWithError responds a json with an error message.
RespondWithJson responds a json with an error message.
RespondWithStatus responds with an HTTP status code.
# Variables
ErrInvalidBookId is an error representing an invalid or malformed book ID.