The following ABNF grammar defines the ZeroMQ Gossip Protocol:

    C:HELLO ( C:PUBLISH / S:PUBLISH / heartbeat )
    heartbeat = C:PING / S:PONG

    ;  Client says hello to server                                           

    HELLO           = signature %d1 version
    signature       = %xAA %xA0             ; two octets
    version         = number-1              ; Version = 1

    ;  Client or server announces a new tuple                                

    PUBLISH         = signature %d2 version key value ttl
    version         = number-1              ; Version = 1
    key             = string                ; Tuple key, globally unique
    value           = longstr               ; Tuple value, as printable string
    ttl             = number-4              ; Time to live, msecs

    ;  Client signals liveness                                               

    PING            = signature %d3 version
    version         = number-1              ; Version = 1

    ;  Server responds to ping; note that pongs are not correlated with      
    ;  pings, and may be mixed with other commands, and the client should    
    ;  treat any incoming traffic as valid activity.                         

    PONG            = signature %d4 version
    version         = number-1              ; Version = 1

    ;  Server rejects command as invalid                                     

    INVALID         = signature %d5 version
    version         = number-1              ; Version = 1

    ; Strings are always length + text contents
    string          = number-1 *VCHAR
    longstr         = number-4 *VCHAR

    ; Numbers are unsigned integers in network byte order
    number-1        = 1OCTET
    number-4        = 4OCTET