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announce, dial, listen - make network connections


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);


These routines establish network connections. Their description uses the following definitions:

is a network address in one of the following forms:

Any directory listed in /net (eg, tcp), or the special token, net. The name net acts as a free variable that stands for any network in common between the source 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).
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. 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 the data or 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 dial routine makes a call to destination addr on a multiplexed network. If the connection server returns several addresses, dial tries each in turn, until a connection is made or no addresses remain to be tried. It returns a Connection containing a file descriptor dfd open for reading and writing the data file in the line directory, and a file descriptor cfd open for reading and writing the 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 Connection structure in which only the cfd descriptor is open, on the control file representing the announcement. Listen takes as its only argument the Connection structure of a successful call to announce. When a call is received, listen returns an open Connection structure as if from dial, except that only the cfd descriptor is open, dfd is nil, and the caller must open the data file for itself.


Make a call and return an open file descriptor to use for communications:

callkremvax(): (int, Connection)
	return sys->dial("tcp!kremvax!80", nil);

Call the local certificate signer:

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




The integer valued functions return 0 on success and -1 on error; the system error string is set. The integer component of the tuple returned by the other functions follows the same convention.


Note that listen does not open the data file.

SYS-DIAL(2 ) Rev:  Thu Feb 15 14:43:27 GMT 2007