dial, hangup, announce, listen, accept, reject, netmkaddr, setnetmtpt, getnetconninfo, freenetconninfo – make and break network connections


#include <u.h>
#include <libc.h>

int dial(char *addr, char *local, char *dir, int *cfdp)

int hangup(int ctl)

int announce(char *addr, char *dir)

int listen(char *dir, char *newdir)

int accept(int ctl, char *dir)

int reject(int ctl, char *dir, char *cause)

char* netmkaddr(char *addr, char *defnet, char *defservice)

void setnetmtpt(char *to, int tolen, char *from)

NetConnInfo* getnetconninfo(char *conndir, int fd)

void freenetconninfo(NetConnInfo*)


For these routines, addr is a network address of the form network!netaddr!service, network!netaddr, or simply netaddr. Network is any directory listed in /net or the special token, net. Net is a free variable that stands for any network in common between the source and the host netaddr. Netaddr can be a host name, a domain name, a network address, or a meta-name of the form $attribute, which is replaced by value from the value-attribute pair attribute=value most closely associated with the source host in the network data base (see ndb(6)).

If a connection attempt is successful and dir is non-zero, the path name of a line directory that has files for accessing the connection is copied into dir. The path name is guaranteed to be less than 40 bytes long. One line directory exists for each possible connection. The data file in the line directory should be used 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.

Dial makes a call to destination addr on a multiplexed network. If the network in addr is net, dial will try all addresses on networks in common between source and destination until a call succeeds. It returns a file descriptor open for reading and writing the data file in the line directory. The addr file in the line directory contains the address called. If the network allows the local address to be set, as is the case with UDP and TCP port numbers, and local is non-zero, the local address will be set to local. If cfdp is non-zero, *cfdp is set to a file descriptor open for reading and writing the control file.

Hangup is a means of forcing a connection to hang up without closing the ctl and data files.

unhandled troff command .P

Announce and listen are the complements of dial. Announce establishes a network name to which calls can be made. Like dial, announce returns an open ctl file. The netaddr used in announce may be a local address or an asterisk, to indicate all local addresses, e.g. tcp!*!echo. The listen routine takes as its first argument the dir of a previous announce. When a call is received, listen returns an open ctl file for the line the call was received on. It sets newdir to the path name of the new line directory. Accept accepts a call received by listen, while reject refuses the call because of cause. Accept returns a file descriptor for the data file opened ORDWR.

Netmkaddr makes an address suitable for dialing or announcing. It takes an address along with a default network and service to use if they are not specified in the address. It returns a pointer to static data holding the actual address to use.

Getnetconninfo returns a structure containing information about a network connection. The structure is:

  typedef struct NetConnInfo NetConnInfo;
  struct NetConnInfo
	char	*dir;		/* connection directory */
	char	*root;		/* network root */
	char	*spec;		/* binding spec */
	char	*lsys;		/* local system */
	char	*lserv;		/* local service */
	char	*rsys;		/* remote system */
	char	*rserv;		/* remote service */
	char	*laddr;		/* local address */
	char	*raddr;		/* remote address */

The information is obtained from the connection directory, conndir. If conndir is nil, the directory is obtained by performing fd2path(2) on fd. Getnetconninfo returns either a completely specified structure, or nil if either the structure can’t be allocated or the network directory can’t be determined. The structure is freed using freenetconninfo.

Setnetmtpt copies the name of the network mount point into the buffer to, whose length is tolen. It exists to merge two pre-existing conventions for specifying the mount point. Commands that take a network mount point as a parameter (such as dns, cs (see ndb(8)), and ipconfig(8)) should now call setnetmtpt. If from is nil, the mount point is set to the default, /net. If from points to a string starting with a slash, the mount point is that path. Otherwise, the mount point is the string pointed to by from appended to the string /net. The last form is obsolete and is should be avoided. It exists only to aid in conversion.


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


int callkremvax(void)
	return dial("kremvax", 0, 0, 0);

Call the local authentication server:


int dialauth(char *service)
	return dial(netmkaddr("$auth", 0, service), 0, 0, 0);

Announce as kremvax on TCP/IP and loop forever receiving calls and echoing back to the caller anything sent:


	int dfd, acfd, lcfd;
	char adir[40], ldir[40];
	int n;
	char buf[256];

	acfd = announce("tcp!*!7", adir);
	if(acfd < 0)
		return -1;
		/* listen for a call */
		lcfd = listen(adir, ldir);
		if(lcfd < 0)
			return -1;
		/* fork a process to echo */
		case -1:
		case 0:
			/* accept the call and open the data file */
			dfd = accept(lcfd, ldir);
			if(dfd < 0)
				return -1;

			/* echo until EOF */
			while((n = read(dfd, buf, sizeof(buf))) > 0)
				write(dfd, buf, n);


/sys/src/libc/9sys, /sys/src/libc/port


auth(2), ip(3), ndb(8)


Dial, announce, and listen return –1 if they fail. Hangup returns nonzero if it fails.