SntpStatus_t Sntp_SerializeRequest()

in source/core_sntp_serializer.c [601:663]

• 38 lines of code
• 5 McCabe index (conditional complexity)

SntpStatus_t Sntp_SerializeRequest( SntpTimestamp_t * pRequestTime,
                                    uint32_t randomNumber,
                                    void * pBuffer,
                                    size_t bufferSize )
{
    SntpStatus_t status = SntpSuccess;

    if( pRequestTime == NULL )
    {
        status = SntpErrorBadParameter;
    }
    else if( pBuffer == NULL )
    {
        status = SntpErrorBadParameter;
    }
    else if( bufferSize < SNTP_PACKET_BASE_SIZE )
    {
        status = SntpErrorBufferTooSmall;
    }

    /* Zero timestamps for client request time is not allowed to protect against
     * attack spoofing server response containing zero value for "originate timestamp".
     * Note: In SNTP/NTP communication, the "originate timestamp" of a valid server response
     * matches the "transmit timestamp" in corresponding client request packet. */
    else if( isZeroTimestamp( pRequestTime ) == true )
    {
        status = SntpErrorBadParameter;
    }
    else
    {
        SntpPacket_t * pRequestPacket = ( SntpPacket_t * ) pBuffer;

        /* Fill the buffer with zero as most fields are zero for a standard SNTP
         * request packet.*/
        ( void ) memset( pBuffer, 0, sizeof( SntpPacket_t ) );

        /* Set the first byte of the request packet for "Version" and "Mode" fields */
        pRequestPacket->leapVersionMode = 0U /* Leap Indicator */ |
                                          ( SNTP_VERSION << SNTP_VERSION_LSB_POSITION ) /* Version Number */ |
                                          SNTP_MODE_CLIENT /* Mode */;


        /* Add passed random number to non-significant bits of the fractions part
         * of the transmit timestamp.
         * This is suggested by the SNTPv4 (and NTPv4) specification(s)
         * to protect against replay attacks. Refer to RFC 4330 Section 3 for
         * more information.
         * Adding random bits to the least significant 16 bits of the fractions
         * part of the timestamp affects only ~15 microseconds of information
         * (calculated as 0xFFFF * 232 picoseconds).
         */
        pRequestTime->fractions = ( pRequestTime->fractions
                                    | ( randomNumber >> 16 ) );

        /* Update the request buffer with request timestamp in network byte order. */
        fillWordMemoryInNetworkOrder( &pRequestPacket->transmitTime.seconds,
                                      pRequestTime->seconds );
        fillWordMemoryInNetworkOrder( &pRequestPacket->transmitTime.fractions,
                                      pRequestTime->fractions );
    }

    return status;
}