=========================== start of opcom_catcher.opt =====================
! Command line: LINK [/NOTRACE] OPCOM_CATCHER /OPT
!
opcom_catcher
poke_pcb
sys$library:vaxcrtl/share
=========================== start of opcom_catcher.c =======================
/*
 * OPCOM_CATCHER.C - catch OPCOM messages.
 */

#include ctype		/* character type */
#include descrip	/* definitions for the descriptor structure */
#include iodef		/* definitions for the function codes */
#include opcdef		/* sndopr message fields */
#include stsdef		/* VMS status code definitions */
#include ttdef		/* terminal characteristics */
#include tt2def		/* extended terminal characteristics */

typedef struct {
  unsigned short status;
  unsigned short len;
  unsigned long devinfo;
} IOSB;

static char dev_name_str [] = "            ";
static $DESCRIPTOR(device_name, dev_name_str);
#define DEVICE_TYPE "LTA"
#define DEVICE_NUM 4444

/*
 * Minimum size of a "real" operator message.
 */
#define MSG_MIN 22

/*
 * Structure of an operator message.
 * Last byte of message is typically <LF> (without <CR>)
 */

typedef struct {
  char junk [MSG_MIN];
  char bell [1];
  char percents_1 [11];
  char spaces_opcom_spaces [9];
  char date_time [23];
  char spaces_after_date_time [2];
  char percents_2 [11];
  char crlf [2];
  char rest [1];	/* actually longer ! */
} OPERATOR_MSG;

static readonly $DESCRIPTOR(mailbox_name, "OPCOM_catcher_mailbox");

#define check(status) {if (! ((status) & STS$M_SUCCESS)) exit(status);}

/*
 * Simplified layout of operator terminal request, which allows us to
 *  fill in everything at compile time.
 */
typedef struct {
  char type;
  char enable;
  short unused;
  long mask;
  short unit;
  char name_len;
  char name [15];
} MY_OPC;

static readonly MY_OPC buffer = {
  OPC$_RQ_TERME,		/* request type */
  1,				/* enable flag */
  0,				/* unused */
  -1,				/* mask for all messages */
  DEVICE_NUM, 			/* unit number */
  sizeof(DEVICE_TYPE) - 1,
  DEVICE_TYPE
};

extern poke_pcb ();

main ()
{
  char inbuf [256];

  struct dsc$descriptor_s oprdesc = {
    (&buffer.name - &buffer.type) + buffer.name_len,
    DSC$K_DTYPE_T,
    DSC$K_CLASS_S,
    &buffer
  };

  IOSB iosb;
  int chan;
  int mbchan;
  int status;
  char *arglist [2] = { 1, &device_name };
  int chars [3];	/* terminal characteristics */

/*
 * Encode the device type and number to form a valid device name.
 */
  sprintf(device_name.dsc$a_pointer, "%s%d:", DEVICE_TYPE, DEVICE_NUM);
  device_name.dsc$w_length = strlen(device_name.dsc$a_pointer);

  status = sys$alloc(&device_name, 0, 0, 0, 0);
  check(status);

  status = sys$crembx(0, &mbchan, 0, 0, 0, 0, &mailbox_name);
  check(status);

/*
 * Assign mailbox channel to terminal.
 */
  status = sys$assign(&device_name, &chan, 0, &mailbox_name);
  check(status);

/*
 * Get the current terminal characteristics, and modify them.
 */
  status = sys$qiow(0, chan, IO$_SENSEMODE, &iosb, 0, 0,
                    chars, sizeof(chars), 0, 0, 0, 0);
  check(status);
  check(iosb.status);

  chars[1] &= ~(TT$M_NOBRDCST);		/* Allow broadcast */
  chars[2] |= TT2$M_BRDCSTMBX;		/* Specify broadcast mailbox */

  status = sys$qiow(0, chan, IO$_SETMODE, &iosb, 0, 0,
                    chars, sizeof(chars), 0, 0, 0, 0);
  check(status);
  check(iosb.status);

/*
 * Hack the process's terminal in the PCB.
 */
  sys$cmkrnl(&poke_pcb, &arglist);

  status = sys$sndopr(&oprdesc, 0);
  check(status);

  while (1) {
    status = sys$qiow(0, mbchan, IO$_READVBLK, &iosb, 0, 0,
                      inbuf, sizeof(inbuf), 0, 0, 0, 0);
    check(status);
    check(iosb.status);

    if (iosb.len > MSG_MIN) {
      OPERATOR_MSG *msg = (OPERATOR_MSG *)inbuf;
      inbuf[iosb.len] = '\0';
/*
 * Here, we can filter the message; it starts at msg->bell.
 * The following code just outputs it.
 */
      {
        struct dsc$descriptor_s outbuf = {
          strlen(msg->bell), DSC$K_DTYPE_T, DSC$K_CLASS_S, &msg->bell
        };
        status = lib$put_output(&outbuf);
        check(status);
      }
    }
  }
}
=========================== start of poke_pcb.mar ==========================
; POKE_PCB.MAR - fudge terminal name in PCB for OPCOM_CATCHER.
;
	.title		poke_pcb
	.library	"sys$share:lib.mlb"
	$pcbdef

	.psect code
.entry	poke_pcb, 0
	movl	4(ap), r0		;get descriptor to r0
	movzbl	(r0), r1		;get string length to r1
	cmpb	r1, #pcb$s_terminal	;must be less than field size
	blss	len_ok
	movb	#pcb$s_terminal-1, r1	;maximum possible size
len_ok:
	movl	4(r0), r0		;get string address to r0
	movb	r1, pcb$t_terminal(r4)		;store length
	movc3	r1, (r0), pcb$t_terminal+1(r4)	;copy terminal name
	movl	#ss$_normal, r0
	ret

	.end
=========================== start of opcom_catcher.com =====================
$! Do MC LATCP CRE PORT LTA4444 (etc) before running this.
$ run /detach -
      /buffer=20000 -
      /page_file=10000 -
      /priv=all -
      /proc="OPCOM catcher" -
      /input=nl: -
      /output=opcom_catcher.log -
      /error=opcom_catcher.log -
      /uic=[1,4] -
opcom_catcher.exe