T_CONNECT(3NSL) Networking Services Library Functions T_CONNECT(3NSL)


t_connect - establish a connection with another transport user


#include <xti.h>

int t_connect(int fd, const struct t_call *sndcall,
struct t_call *rcvcall);


This routine is part of the XTI interfaces which evolved from the TLI
interfaces. XTI represents the future evolution of these interfaces.
However, TLI interfaces are supported for compatibility. When using a TLI
routine that has the same name as an XTI routine, the tiuser.h header
file must be used. Refer to the TLI COMPATIBILITY section for a
description of differences between the two interfaces. This function
enables a transport user to request a connection to the specified
destination transport user.

This function can only be issued in the T_IDLE state. The parameter fd
identifies the local transport endpoint where communication will be
established, while sndcall and rcvcall point to a t_call structure which
contains the following members:

struct netbuf addr;
struct netbuf opt;
struct netbuf udata;
int sequence;

The parameter sndcall specifies information needed by the transport
provider to establish a connection and rcvcall specifies information that
is associated with the newly established connection.

In sndcall, addr specifies the protocol address of the destination
transport user, opt presents any protocol-specific information that might
be needed by the transport provider, udata points to optional user data
that may be passed to the destination transport user during connection
establishment, and sequence has no meaning for this function.

On return, in rcvcall, addr contains the protocol address associated with
the responding transport endpoint, opt represents any protocol-specific
information associated with the connection, udata points to optional user
data that may be returned by the destination transport user during
connection establishment, and sequence has no meaning for this function.

The opt argument permits users to define the options that may be passed
to the transport provider. The user may choose not to negotiate protocol
options by setting the len field of opt to zero. In this case, the
provider uses the option values currently set for the communications

If used, sndcall->opt.buf must point to a buffer with the corresponding
options, and sndcall->opt.len must specify its length. The maxlen and
buf fields of the netbuf structure pointed by rcvcall->addr and
rcvcall->opt must be set before the call.

The udata argument enables the caller to pass user data to the
destination transport user and receive user data from the destination
user during connection establishment. However, the amount of user data
must not exceed the limits supported by the transport provider as
returned in the connect field of the info argument of t_open(3NSL) or
t_getinfo(3NSL). If the len of udata is zero in sndcall, no data will be
sent to the destination transport user.

On return, the addr, opt and udata fields of rcvcall will be updated to
reflect values associated with the connection. Thus, the maxlen field of
each argument must be set before issuing this function to indicate the
maximum size of the buffer for each. However, maxlen can be set to zero,
in which case no information to this specific argument is given to the
user on the return from t_connect(). If maxlen is greater than zero and
less than the length of the value, t_connect() fails with t_errno set to
TBUFOVFLW. If rcvcall is set to NULL, no information at all is

By default, t_connect() executes in synchronous mode, and will wait for
the destination user's response before returning control to the local
user. A successful return (that is, return value of zero) indicates that
the requested connection has been established. However, if O_NONBLOCK is
set by means of t_open(3NSL) or fcntl(2), t_connect() executes in
asynchronous mode. In this case, the call will not wait for the remote
user's response, but will return control immediately to the local user
and return -1 with t_errno set to TNODATA to indicate that the
connection has not yet been established. In this way, the function simply
initiates the connection establishment procedure by sending a connection
request to the destination transport user. The t_rcvconnect(3NSL)
function is used in conjunction with t_connect() to determine the status
of the requested connection.

When a synchronous t_connect() call is interrupted by the arrival of a
signal, the state of the corresponding transport endpoint is T_OUTCON,
allowing a further call to either t_rcvconnect(3NSL), t_rcvdis(3NSL) or
t_snddis(3NSL). When an asynchronous t_connect() call is interrupted by
the arrival of a signal, the state of the corresponding transport
endpoint is T_IDLE.


Upon successful completion, a value of 0 is returned. Otherwise, a
value of -1 is returned and t_errno is set to indicate an error.




On failure, t_errno is set to one of the following:

The user does not have permission to use the specified
address or options.

This transport provider does not support multiple
connections with the same local and remote addresses. This
error indicates that a connection already exists.

The specified protocol address was in an incorrect format
or contained illegal information.

The amount of user data specified was not within the
bounds allowed by the transport provider.

The specified file descriptor does not refer to a
transport endpoint.

The specified protocol options were in an incorrect format
or contained illegal information.

The number of bytes allocated for an incoming argument
(maxlen) is greater than 0 but not sufficient to store the
value of that argument. If executed in synchronous mode,
the provider's state, as seen by the user, changes to
T_DATAXFER, and the information to be returned in rcvcall
is discarded.

An asynchronous event has occurred on this transport
endpoint and requires immediate attention.

O_NONBLOCK was set, so the function successfully initiated
the connection establishment procedure, but did not wait
for a response from the remote user.

This function is not supported by the underlying transport

The communications endpoint referenced by fd is not in
one of the states in which a call to this function is

This error indicates that a communication problem has been
detected between XTI and the transport provider for which
there is no other suitable XTI error (t_errno).

A system error has occurred during execution of this


The XTI and TLI interface definitions have common names but use different
header files. This, and other semantic differences between the two
interfaces are described in the subsections below.

Interface Header

The XTI interfaces use the header file, xti.h. TLI interfaces should not
use this header. They should use the header:

#include <tiuser.h>

Error Description Values

The TPROTO and TADDRBUSY t_errno values can be set by the XTI interface
but not by the TLI interface.

A t_errno value that this routine can return under different
circumstances than its XTI counterpart is TBUFOVFLW. It can be returned
even when the maxlen field of the corresponding buffer has been set to

Option Buffers

The format of the options in an opt buffer is dictated by the transport
provider. Unlike the XTI interface, the TLI interface does not fix the
buffer format.


See attributes(7) for descriptions of the following attributes:

|MT Level | Safe |


fcntl(2), t_accept(3NSL), t_alloc(3NSL), t_getinfo(3NSL), t_listen(3NSL),
t_open(3NSL), t_optmgmt(3NSL), t_rcvconnect(3NSL), t_rcvdis(3NSL),
t_snddis(3NSL), attributes

May 7, 1998 T_CONNECT(3NSL)