SilcBool silc_argument_get_decoded(SilcArgumentPayload payload,
                                       SilcUInt32 type,
                                       SilcArgumentDecodeType dec_type,
                                       void *ret_arg,
                                       void *ret_arg_alloc);

    Returns decoded argument by type.  This is a helper function to
    decode common argument types directly.  The `type' is the argument
    type number in the payload, and the `dec_type' is the type the
    argument is decoded to.  If the `ret_arg' is non-NULL then the
    decodec data is returned into that pointer.  If the `ret_arg_alloc'
    is non-NULL then this function will allocate the decoded data and
    will return the pointer into `ret_arg_alloc'.  Some types must always
    be allocated; see SilcArgumentDecodeType.

    Return TRUE if the argument was present and waa successfully decoded.
    FALSE if it is not present, or could not be decoded.

    SilcID id;
    SilcPublicKey public_key;

    if (!silc_argument_get_decoded(args, 2, SILC_ARGUMENT_ID, &id, NULL))
      error;

    if (!silc_argument_get_decoded(args, 4, SILC_ARGUMENT_PUBLIC_KEY,
                                   NULL, &public_key))
      error;