t_connect

- establish a connection with another transport user

Synopsis

#include <xti.h>

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

Description

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 endpoint.

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 returned.

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.

Return Values

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.

VALID STATES

T_IDLE

Errors

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

TACCES

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

TADDRBUSY

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

TBADADDR

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

TBADDATA

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

TBADF

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

TBADOPT

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

TBUFOVFLW

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.

TLOOK

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

TNODATA

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

TNOTSUPPORT

This function is not supported by the underlying transport provider.

TOUTSTATE

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

TPROTO

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).

TSYSERR

A system error has occurred during execution of this function.

TLI COMPATIBILITY

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 zero.

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.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

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