Control Operations

High-level protocols and sessions may request information from or change the state of ASP protocol and session objects by calling the following two control functions. If the opcode used in the call is not recognized by the ASP control function, one of IP's control functions is called with the same opcode. In these routines checkLen is a simple macro that makes sure the the buffer len is large enough to hold the value being returned.

static int
aspControlProtl(Protl self, int opcode, char *buf, int len)
{
    switch (opcode) {
        case GETMAXPACKET:
        case GETOPTPACKET:
            checkLen(len, sizeof(int));
            if (xControlProtl(xGetProtlDown(self, 0), opcode, buf, len) <
                    sizeof(int))
                return -1;
            *(int *)buf -= HLEN;
            return sizeof(int);
        default:
            return xControlProtl(xGetProtlDown(self, 0), opcode, buf, len);
    }
}

static int
aspControlSessn(Sessn self, int opcode, char *buf, int len)
{
    SessnState *sstate = (SessnState *)self->state;
    ASPhdr     *hdr;

    hdr = &(sstate->hdr);
    switch (opcode) {
        case GETMYPROTO:
            checkLen(len, sizeof(long));
            *(long *)buf = sstate->hdr.sport;
            return sizeof(long);
        case GETPEERPROTO:
            checkLen(len, sizeof(long));
            *(long *)buf = sstate->hdr.dport;
            return sizeof(long);
        case GETMAXPACKET:
        case GETOPTPACKET:
            checkLen(len, sizeof(int));
            if (xControlSessn(xGetSessnDown(self, 0), opcode, buf, len) <
                    sizeof(int))
                return -1;
            *(int *)buf -= HLEN;
            return sizeof(int);
        default:
            return xControlSessn(xGetSessnDown(self, 0), opcode, buf, len);
    }
}

In addition to invoking these control operations on low-level protocols and sessions, high-level entities can query ASP for participants associated with the session. This is done by invoking xGetParticipants on the session. The ASP-specific implementation of this operation turns around and asks the session below it (i.e., an IP session) for the same information.

static Part *
aspGetParticipants(Sessn self)
{
    Part       *p;
    int        numParts;
    SessnState *sstate = (SessnState *)self->state;
    long       localPort, remotePort;

    p = xGetParticipants(xGetSessnDown(self, 0));
    if (!p)
        return NULL;
    numParts = partLength(p);
    if (numParts > 0 && numParts <= 2) {
        if (numParts == 2) {
            localPort = (long)sstate->hdr.sport;
            partPush(p[1], (void *)&localPort, sizeof(long));
        }
        remotePort = (long)sstate->hdr.dport;
        partPush(p[0], (void *)&remotePort, sizeof(long));
        return p;
    }
    else    /* Bad number of participants */
        return NULL;
}