cnet v2.0.5

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cnet's datatypes, event types, and error types

cnet's provides a small number of data- and enumerated types, each defined in the <cnet.h> header file.

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The CnetNodeType enumerated type

Each node is either a host (a workstation) or a router. The type of a node may be determined by examining its value of nodeinfo.nodetype. For example:
    if(nodeinfo.nodetype == NT_HOST)
        (void)CNET_set_handler(EV_APPLICATIONREADY, appl_ready, 0);

CnetNodeType meaning
NT_HOST this node is a host with an Application Layer and keyboard
NT_ROUTER this node is a router without an Application Layer or keyboard

Note that calls to the functions

    CNET_write_application,
    CNET_read_application,
    CNET_enable_application,
    CNET_disable_application and
    CNET_set_handler(EV_APPLICATIONLAYER,...) or
    CNET_set_handler(EV_KEYBOARDREADY,...)

are only valid if called from a node of node type NT_HOST.

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The CnetLinkType enumerated type

Each node's link is either a LOOPBACK, an Ethernet, or a point-to-point link. The type of a link may be determined by examining the value of linkinfo[link].linktype. For example:
    if(linkinfo[link].linktype == LT_ETHERNET)
        (void)CNET_set_promiscuous(link, 1);

CnetNodeType meaning
LT_LOOPBACK this link (which will always be link 0) is used to quickly deliver data from a node to itself
LT_ETHERNET this link connects this node to other nodes via a shared Ethernet segment
LT_POINT2POINT this link connects this node to one other node via a dedicated (``private'') link as in a wide-area network

Calls to the functions

    CNET_set_promiscuous, and
    CNET_set_nicaddr
cannot set the attributes of link 0, the LOOPBACK link, nor set a NIC address to either the zero address, 00:00:00:00:00:00, or the broadcast address, ff:ff:ff:ff:ff:ff.

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The CnetNicaddr datatype

Each Physical Layer link of type LT_ETHERNET or LT_POINT2POINT has a specific Network Interface Card (NIC) address. cnet provides the CnetNicaddr datatype to represent the addresses of its NICs, as an array of LEN_NICADDR (=6) unsigned characters.

Frames written to Ethernet links are ``expected'' to carry the address of their destination Network Interface Card (NIC) at the very beginning of the frame. cnet interprets the leading LEN_NICADDR bytes of each frame on an Ethernet segment to be an address. The special address, whose string representation is ff:ff:ff:ff:ff:ff, is interpreted as the Ethernet broadcast address. Any frame carrying the broadcast address as its destination address will be delivered to all NICs on the Ethernet segment, except the sender. cnet does not support multicast or group addressing.

cnet provides the functions CNET_parse_nicaddr and CNET_format_nicaddr to convert between character strings and the CnetNicaddr datatype.

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The CnetInt64 datatype

As of v2.0, cnet supports a 64-bit integer datatype named CnetInt64 which is used to store all times (now in microseconds) and large statistics. The datatype and a number of arithmetic, conversion, and I/O routines are defined in the <cnet64bits.h> header file which, like the <cnet.h> header file (and included by it), is located via the value of CNETPATH. The CnetInt64 datatype is fully described on its own webpage.

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The CnetEvent enumerated type

Events occur in cnet when a node reboots, the Application Layer has a message for delivery, the Physical Layer receives a frame on a link, the keyboard provides a line of input, a link changes state (either up or down), a timer event expires, a debugging button (under X-windows) is selected, and a node is (politely) shutdown (no event is delivered if a node pauses, crashes or suffers a hardware failure). All such events are of type CnetEvent. Interest may be registered in each event with CNET_set_handler; events are received as the first parameter of each event handler, and their invocation may be traced with CNET_set_trace.

CnetEvent meaning
EV_NULL this event is used internally and is never seen by your protocols
EV_REBOOT raised as reboot_node(EV_REBOOT, ... , ...)
EV_SHUTDOWN raised before cnet is (cleanly) terminated
EV_APPLICATIONREADY raised when there is a message ready for delivery
EV_PHYSICALREADY raised when a frame arrives at one of the links
EV_KEYBOARDREADY raised when an input line is entered from the keyboard
EV_LINKSTATE raised when a link changes state (either up or down)
EV_DRAWFRAME raised when a frame is to be drawn in 2-node world
EV_DEBUG1..EV_DEBUG5 raised when one of the debug buttons (under X-windows) is pressed
EV_TIMER1..EV_TIMER10 raised when a timer on any of the 10 timer queues expires

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The CnetError enumerated type

Most cnet library functions return the integer 0 on success and the integer -1 on failure. The most recent error status is reflected in the global variable cnet_errno. All values of cnet_errno will be instances of the enumerated type CnetError. Errors may be reported to stderr with cnet_perror() and their error message string accessed from cnet_errstr[(int)cnet_errno]. For example:
    if(CNET_write_application(msgbuffer, &msglength) != 0) {
        /* an error has occured */
        if(cnet_errno == ER_BADSESSION) {
            /* handle this special case */
            ....
        }
        else {
            cnet_perror("writing to application");
        }
    }

CnetError meaning
ER_OK No error
ER_BADARG Invalid argument passed to a function
ER_BADEVENT Invalid event passed to a function
ER_BADLINK Invalid link number passed to a function
ER_BADNODE Invalid node passed to a function
ER_BADSENDER Application Layer given message from an unknown node
ER_BADSESSION Application Layer given message from incorrect session
ER_BADSIZE Indicated length is of incorrect size
ER_BADTIMER Invalid CnetTimer passed to a function
ER_CORRUPTDATA Attempt to transfer corrupt data (only seen if -e provided)
ER_LINKDOWN Attempt to transmit on a link which is down
ER_NOTFORME Application Layer given a message for another node
ER_NOTREADY Function called when service not available
ER_NOTSUPPORTED Invalid operation for this node type
ER_OUTOFSEQ Application Layer given message out of sequence
ER_TOOBUSY link is too busy/congested to handle request

cnet was written and is maintained by Chris McDonald (chris@csse.uwa.edu.au)