q Algorithm

Last updated June 1, 2012.

(qPT = q Protocol Type - example: qAU = q APRS UDP)

All packets
{
    Place into TNC-2 format
    If a q construct is last in the path (no call following the qPT)
        delete the qPT
}

All packets from an inbound connection that would normally be passed per current validation algorithm:
{
    If the packet entered the server directly (without login) from an UDP port:
    {
        if a q construct with a single call exists in the packet
            Replace the q construct with ,qAU,SERVERLOGIN
        else if more than a single call exists after the q construct
            Invalid header, drop packet as error
        else
            Append ,qAU,SERVERLOGIN
        Quit q processing
    }

    If the packet entered the server from an unverified connection
        AND the FROMCALL equals the client login 
        AND the header has been successfully converted to TCPXX format (per current validation algorithm):
    {
        (All packets not deemed "OK" from an unverified connection should be dropped.)
        if a q construct exists in the path
            Replace the q construct with ,qAX,SERVERLOGIN
        else
            Append ,qAX,SERVERLOGIN
        Quit q processing
    }
    
    If the packet entered the server from a verified client-only connection
        AND the FROMCALL does not match the login:
    {
        if a q construct exists in the path
            if the q construct equals ,qAR,callsignssid or ,qAr,callsignssid
                Replace qAR or qAr with qAo
            else if the q construct equals ,qAS,callsignssid
                Replace qAS with qAO
            else if the q construct equals ,qAC,callsignssid and callsignssid is not equal to the servercall or login
                Replace qAC with qAO
        else if the path is terminated with ,callsignssid,I
            Replace ,callsignssid,I with qAo,callsignssid
        else
            Append ,qAO,login
        Skip to "All packets with q constructs"
    }
    
    If a q construct exists in the header:
        Skip to "All packets with q constructs"
        
    If header is terminated with ,I:
    {
        If the VIACALL preceding the ,I matches the login:
            Change from ,VIACALL,I to ,qAR,VIACALL
        Else
            Change from ,VIACALL,I to ,qAr,VIACALL
    }
    Else If the FROMCALL matches the login:
    {
        if port is send-only (UDP/HTTP)
            Append ,qAO,SERVERLOGIN
        else
            Append ,qAC,SERVERLOGIN
        Quit q processing
    }
    Else
        Append ,qAS,login
    Skip to "All packets with q constructs"
}

If packet entered the server from an outbound connection (to another server's port 1313, for instance)
    AND no q construct exists in the header:
{
    If header is terminated with ,I:
        Change from ,VIACALL,I to ,qAr,VIACALL
    Else
        Append ,qAS,IPADDR (IPADDR is an 8 character hex representation of the IP address of the remote server)(DEPRICATED)
}
        
All packets with q constructs:
{
    if ,qAZ, is the q construct:
    {
        Dump to the packet to the reject log
        Quit processing the packet
    }
    
    If ,SERVERLOGIN is found after the q construct:
    {
        Dump to the loop log with the sender's IP address for identification
        Quit processing the packet
    }

    If a callsign-SSID is found twice in the q construct:
    {
        Dump to the loop log with the sender's IP address for identification
        Quit processing the packet
    }
    
    If a verified login other than this login is found in the q construct
        AND that login is not allowed to have multiple verified connects
        (the IPADDR of an outbound connection is considered a verified login):
    {
        Dump to the loop log with the sender's IP address for identification
        Quit processing the packet
    }
    
    If the packet is from an inbound port 
        AND the login is found after the q construct but is not the LAST VIACALL:
    {
        Dump to the loop log with the sender's IP address for identification
        Quit processing the packet
    }
    
    If trace is on, the q construct is qAI, or the FROMCALL is on the server's trace list:
    {
        If the packet is from a verified port where the login is not found after the q construct:
            Append ,login
        else if the packet is from an outbound connection
            Append ,IPADDR
        
        Append ,SERVERLOGIN
    }
}