include "sys.m";
sys:= load Sys Sys->PATH;
Connection: adt
{
  dfd: ref FD; # data file
  cfd: ref FD; # control file
  dir: string; # pathname of line directory
};
announce: fn(addr: string):          (int, Connection);
dial:     fn(addr, local: string):   (int, Connection);
listen:   fn(c: Connection):         (int, Connection);
export:   fn(fd: ref FD, flag: int):  int;

dial (addr, local)

The addr Argument

network!destination!serviceport

For more information about the structure of this address, see Request Format in Chapter 6

The Connection Server

If the connection server daemon is not running, the dial function silently skips the translation stage and attempts to open a network connection with addr as received.

The cs daemon is accessed by an interface file also called cs. The dial function looks for this file in the following directories in the OR'ed listed:

1. A directory named in an optional prefix to the addr argument. The format in such cases is: /dir/network!destination!serviceport
2. The /net directory
3. The /net.alt directory. If the connection server returns several network addresses for the named destination, the dial function tries each in the order received until a connection is made.

At the completion of dial, local can be read from the local file of the network interface.

The Return Values

On failure, the dial function returns -1 in the integer portion of the tuple.

On success, the members of the returned Connection adt have been initialized to the following values:

dir	The pathname to the directory containing the network interface files for the connection. For example, /net/tcp/5.
dfd	A file descriptor to the data file of the connection. This is used to read and write data to the destination.
cfd	A file descriptor for the ctl file of the connection. Commands can be sent to this file to control the connection.

See the appropriate Network device pages (for example, ip - TCP, UDP network protocols over IP in Chapter 2) for further details of using this interface.

announce (addr)

The Argument, addr

network!localname!serviceport

The localname component is translated (if possible) by the connection server. The result is stored in the local file of the network interface. That file can be used for display purposes. The localname value is not used by the underlying network. The setting of local file is skipped if localname is'*'.

The Connection Server

The cs daemon is accessed by an interface file also called cs. The announce function looks for that file in two directories in the following order:

1. A directory named in an optional prefix to the addr argument. The format in such cases is: /dir/network!*!serviceport
2. The /net directory

listen(c)

Argument

Return Values

When a call is received, listen includes an open Connection adt that leads to a network interface file. The data file of that interface is cross connected (read-to-write and write-to-read) to the data file associated with the Connection adt returned by the dial function to the client process.

export (fd, flag)

The export function can take two mutually exclusive flags

EXPWAIT	The export function blocks until all client requests are complete.
EXPASYNC	Client requests are handled by a background thread, while export returns immediately

:

Return Values

Examples

callkremvax( ): (int, Connection)
{
    return sys->dial("tcp!kremvax!mpeg", nil);
}

dialauth(service: string): (int, Connection) { return sys->dial("net!$SIGNER!inflogin", nil); }