ngtcp2_pkt_decode_version_cid
=============================

Synopsis
--------

*#include <ngtcp2/ngtcp2.h>*

.. function:: int ngtcp2_pkt_decode_version_cid(ngtcp2_version_cid *dest, const uint8_t *data, size_t datalen, size_t short_dcidlen)

    
    `ngtcp2_pkt_decode_version_cid` extracts QUIC version, Destination
    Connection ID and Source Connection ID from the packet pointed by
    *data* of length *datalen*.  This function can handle Connection ID
    up to 255 bytes unlike `ngtcp2_pkt_decode_hd_long` or
    `ngtcp2_pkt_decode_hd_short` which are only capable of handling
    Connection ID less than or equal to :macro:`NGTCP2_MAX_CIDLEN`.
    Longer Connection ID is only valid if the version is unsupported
    QUIC version.
    
    If the given packet is Long header packet, this function extracts
    the version from the packet, and assigns it to
    :member:`dest->version <ngtcp2_version_cid.version>`.  It also
    extracts the pointer to the Destination Connection ID and its
    length, and assigns them to :member:`dest->dcid
    <ngtcp2_version_cid.dcid>` and :member:`dest->dcidlen
    <ngtcp2_version_cid.dcidlen>` respectively.  Similarly, it extracts
    the pointer to the Source Connection ID and its length, and assigns
    them to :member:`dest->scid <ngtcp2_version_cid.scid>` and
    :member:`dest->scidlen <ngtcp2_version_cid.scidlen>` respectively.
    *short_dcidlen* is ignored.
    
    If the given packet is Short header packet, :member:`dest->version
    <ngtcp2_version_cid.version>` will be 0, :member:`dest->scid
    <ngtcp2_version_cid.scid>` will be ``NULL``, and
    :member:`dest->scidlen <ngtcp2_version_cid.scidlen>` will be 0.
    Because the Short header packet does not have the length of
    Destination Connection ID, the caller has to pass the length in
    *short_dcidlen*.  This function extracts the pointer to the
    Destination Connection ID, and assigns it to :member:`dest->dcid
    <ngtcp2_version_cid.dcid>`.  *short_dcidlen* is assigned to
    :member:`dest->dcidlen <ngtcp2_version_cid.dcidlen>`.
    
    If Version Negotiation is required, this function returns
    :macro:`NGTCP2_ERR_VERSION_NEGOTIATION`.  Unlike the other error
    cases, all fields of *dest* are assigned as described above.
    
    This function returns 0 if it succeeds.  Otherwise, one of the
    following negative error code:
    
    :macro:`NGTCP2_ERR_INVALID_ARGUMENT`
        The function could not decode the packet header.
    :macro:`NGTCP2_ERR_VERSION_NEGOTIATION`
        Version Negotiation packet should be sent.