Source code for multicodec.multicodec

import varint

from .constants import NAME_TABLE, CODE_TABLE


def extract_prefix(bytes_):
    """
    Extracts the prefix from multicodec prefixed data

    :param bytes bytes_: multicodec prefixed data
    :return: prefix for the prefixed data
    :rtype: bytes
    :raises ValueError: when incorrect varint is provided
    """
    try:
        return varint.decode_bytes(bytes_)
    except TypeError:
        raise ValueError('incorrect varint provided')


def get_prefix(multicodec):
    """
    Returns prefix for a given multicodec

    :param str multicodec: multicodec codec name
    :return: the prefix for the given multicodec
    :rtype: byte
    :raises ValueError: if an invalid multicodec name is provided
    """
    try:
        prefix = varint.encode(NAME_TABLE[multicodec])
    except KeyError:
        raise ValueError('{} multicodec is not supported.'.format(multicodec))
    return prefix


def add_prefix(multicodec, bytes_):
    """
    Adds multicodec prefix to the given bytes input

    :param str multicodec: multicodec to use for prefixing
    :param bytes bytes_: data to prefix
    :return: prefixed byte data
    :rtype: bytes
    """
    prefix = get_prefix(multicodec)
    return b''.join([prefix, bytes_])


def remove_prefix(bytes_):
    """
    Removes prefix from a prefixed data

    :param bytes bytes_: multicodec prefixed data bytes
    :return: prefix removed data bytes
    :rtype: bytes
    """
    prefix_int = extract_prefix(bytes_)
    prefix = varint.encode(prefix_int)
    return bytes_[len(prefix):]


def get_codec(bytes_):
    """
    Gets the codec used for prefix the multicodec prefixed data

    :param bytes bytes_: multicodec prefixed data bytes
    :return: name of the multicodec used to prefix
    :rtype: str
    """
    prefix = extract_prefix(bytes_)
    try:
        return CODE_TABLE[prefix]
    except KeyError:
        raise ValueError('Prefix {} not present in the lookup table'.format(prefix))


def is_codec(name):
    """
    Check if the codec is a valid codec or not

    :param str name: name of the codec
    :return: if the codec is valid or not
    :rtype: bool
    """
    return name in NAME_TABLE