include "dial.m";
dial := load Dial Dial->PATH;

Connection: adt
{
    dfd:  ref FD;  # data file
    cfd:  ref FD;  # control file
    dir:  string;  # pathname of line directory
};

announce:  fn(addr: string):        ref Connection;
dial:      fn(addr, local: string): ref Connection;
listen:    fn(c: ref Connection):       ref Connection;
accept:    fn(c: ref Connection): ref Sys->FD;
reject:    fn(c: ref Connection, why: string);

netmkaddr: fn(addr, defnet, defsvc: string): string;

Conninfo: adt
{
    dir:   string;   # connection directory
    root:  string;   # network mount point
    spec:  string;   # its binding spec
    lsys:  string;   # local host address
    lserv: string;   # local service
    rsys:  string;   # remote host address
    rserv: string;   # remote service
    laddr: string;   # local address in dial form
    raddr: string;   # remote address in dial form
};

netinfo:   fn(c: ref Connection): ref Conninfo;

addr

is a network address in one of the following forms:

network!netaddr!service
network!netaddr
netaddr

network

Any directory listed in /net (eg, tcp), or the special token, net. The special name net stands for any network that connects the current host and netaddr. A network name can be preceded by the full path name of a directory of networks, using the form /dir/network (eg, /net.alt/tcp).

netaddr

A host name, a domain name, a network address, or a meta-name of the form $attribute, which is replaced by value from the corresponding attribute-value pair in the connection server data base (see db(6)).

The functions dial and announce translate a given addr to an actual network address using the connection server cs(8). If a logical name addr corresponds to several network addresses, for instance if a destination machine has several interfaces, cs will return them all; dial or announce will try each in turn until one works. In particular, if addr is net, cs will return addresses on all networks that are common to source and destination. The translation procedure accesses cs using its interface file cs, which is sought as follows: first, in an explicit directory /dir if one was given in network; second, in the standard directory /net; and finally in the directory /net.alt (dial only). If the connection server cannot be found, the addr is used as-is.

If a connection attempt is successful, the dir member of the resulting Connection will be the path name of a line directory that has files for accessing the connection. One line directory exists for each possible connection. The data file in the line directory is opened to make a connection, and read and written to communicate with the destination. The ctl file in the line directory can be used to send commands to the line. See ip(3) for messages that can be written to the ctl file. The last close of both data and ctl file will close the connection. The remote file in the line directory contains the address called; the file local contains the local address assigned.

The function dial calls destination addr on a multiplexed network. If the connection server returns several possible locations for addr, dial tries each in turn, until a connection is made, or no address remains to be tried. Dial returns a reference to a Connection value containing a string dir that names the conversation directory for the connection, a file descriptor dfd open for reading and writing the data file in that directory, and a file descriptor cfd open for reading and writing the directory's ctl file. If local is non-empty, and the network allows the local address to be set, as is the case with UDP and TCP port numbers, the local address will be set to local.

Announce and listen are the complements of dial. Announce establishes a network name to which incoming calls can be made. In addr, netaddr gives the name or address of one of the local host's interfaces on which to listen for calls to the given service; it can be * to listen for calls on any interface on network. Announce returns a reference to a Connection value in which only the cfd descriptor is open, on the control file representing the announcement. Listen takes as its only argument a reference to the Connection returned by a successful call to announce. When a call is received, listen returns a reference to a new Connection value that refers to the conversation directory for the incoming call; only the cfd descriptor is open. That call can be accepted or rejected. Use accept to obtain a file descriptor for the data file for the conversation. Use reject to reject the incoming call; some networks will also tell the caller the reason why.

Netmkaddr makes addr into a full network address, suitable for dial or announce. It adds the default network defnet (usually "net") and a default service defsvc to the given addr as required, including `!' separators, and returns the result.

Given a Connection, netinfo returns a reference to a Conninfo value that gives details about the connection and its network.

callkremvax(): ref Sys->FD
{
	c := dial->dial("tcp!kremvax!80", nil);
	if(c == nil)
		return nil;
	return c.dfd;
}

Call the local certificate signer:

dialsigner(service: string): ref Sys->FD
{
	c := dial->dial("net!$SIGNER!inflogin", nil);
	if(c == nil)
		return nil;
	return c.dfd;
}

Listen for incoming calls.

listener()
{
	ac := dial->announce("tcp!*!9995");
	if(ac == nil){
		sys->print("can't announce: %r\n");
		exit;
	}
	for(;;){
		lc := dial->listen(ac);
		if(lc == nil){
			sys->print("listen: %r\n");
			exit;
		}
		sys->print("incoming: %s\n", hd ctext(lc));
		spawn client(lc);
	}
}

client(c: ref Connection)
{
	dfd := dial->accept(c);
	if(dfd == nil){
		sys->print("%s: can't accept: %r\n", c.dir);
		exit;
	}
	buf := array[Sys->ATOMICIO] of byte;
	while((n := sys->read(dfd, buf, len buf)) > 0)
		sys->write(dfd, buf, n);
}