Tribblix: manual page: t

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

NAME

t_snd - send data or expedited data over a connection

SYNOPSIS

#include <xti.h>

int t_snd(int fd, void *buf, unsigned int nbytes, int flags);

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 is used to send either normal or expedited data. The
argument fd identifies the local transport endpoint over which data
should be sent, buf points to the user data, nbytes specifies the
number of bytes of user data to be sent, and flags specifies any
optional flags described below:

T_EXPEDITED
If set in flags, the data will be sent as expedited
data and will be subject to the interpretations of
the transport provider.

T_MORE
If set in flags, this indicates to the transport
provider that the transport service data unit (TSDU)
(or expedited transport service data unit - ETSDU) is
being sent through multiple t_snd() calls. Each
t_snd() with the T_MORE flag set indicates that
another t_snd() will follow with more data for the
current TSDU (or ETSDU).

The end of the TSDU (or ETSDU) is identified by a
t_snd() call with the T_MORE flag not set. Use of
T_MORE enables a user to break up large logical data
units without losing the boundaries of those units at
the other end of the connection. The flag implies
nothing about how the data is packaged for transfer
below the transport interface. If the transport
provider does not support the concept of a TSDU as
indicated in the info argument on return from
t_open(3NSL) or t_getinfo(3NSL), the T_MORE flag is
not meaningful and will be ignored if set.

The sending of a zero-length fragment of a TSDU or
ETSDU is only permitted where this is used to
indicate the end of a TSDU or ETSDU; that is, when
the T_MORE flag is not set. Some transport providers
also forbid zero-length TSDUs and ETSDUs.

T_PUSH
If set in flags, requests that the provider transmit
all data that it has accumulated but not sent. The
request is a local action on the provider and does
not affect any similarly named protocol flag (for
example, the TCP PUSH flag). This effect of setting
this flag is protocol-dependent, and it may be
ignored entirely by transport providers which do not
support the use of this feature.

Note that the communications provider is free to collect data in a
send buffer until it accumulates a sufficient amount for
transmission.

By default, t_snd() operates in synchronous mode and may wait if flow
control restrictions prevent the data from being accepted by the
local transport provider at the time the call is made. However, if
O_NONBLOCK is set by means of t_open(3NSL) or fcntl(2), t_snd() will
execute in asynchronous mode, and will fail immediately if there are
flow control restrictions. The process can arrange to be informed
when the flow control restrictions are cleared by means of either
t_look(3NSL) or the EM interface.

On successful completion, t_snd() returns the number of bytes
(octets) accepted by the communications provider. Normally this will
equal the number of octets specified in nbytes. However, if
O_NONBLOCK is set or the function is interrupted by a signal, it is
possible that only part of the data has actually been accepted by the
communications provider. In this case, t_snd() returns a value that
is less than the value of nbytes. If t_snd() is interrupted by a
signal before it could transfer data to the communications provider,
it returns -1 with t_errno set to TSYSERR and errno set to EINTR.

If nbytes is zero and sending of zero bytes is not supported by the
underlying communications service, t_snd() returns -1 with t_errno
set to TBADDATA.

The size of each TSDU or ETSDU must not exceed the limits of the
transport provider as specified by the current values in the TSDU or
ETSDU fields in the info argument returned by t_getinfo(3NSL).

The error TLOOK is returned for asynchronous events. It is required
only for an incoming disconnect event but may be returned for other
events.

RETURN VALUES

On successful completion, t_snd() returns the number of bytes
accepted by the transport provider. Otherwise, -1 is returned on
failure and t_errno is set to indicate the error.

Note that if the number of bytes accepted by the communications
provider is less than the number of bytes requested, this may either
indicate that O_NONBLOCK is set and the communications provider is
blocked due to flow control, or that O_NONBLOCK is clear and the
function was interrupted by a signal.

ERRORS

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

TBADDATA
Illegal amount of data:

o A single send was attempted specifying a
TSDU (ETSDU) or fragment TSDU (ETSDU)
greater than that specified by the current
values of the TSDU or ETSDU fields in the
info argument.

o A send of a zero byte TSDU (ETSDU) or zero
byte fragment of a TSDU (ETSDU) is not
supported by the provider.

o Multiple sends were attempted resulting in
a TSDU (ETSDU) larger than that specified
by the current value of the TSDU or ETSDU
fields in the info argument - the ability
of an XTI implementation to detect such an
error case is implementation-dependent. See
WARNINGS, below.

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

TBADFLAG
An invalid flag was specified.

TFLOW
O_NONBLOCK was set, but the flow control mechanism
prevented the transport provider from accepting any
data at this time.

TLOOK
An asynchronous event has occurred on this transport
endpoint.

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 t_errno values that can be set by the XTI interface and cannot be
set by the TLI interface are:
TPROTO
TLOOK
TBADFLAG
TOUTSTATE

The t_errno values that this routine can return under different
circumstances than its XTI counterpart are:
TBADDATA

In the TBADDATA error cases described above, TBADDATA is returned,
only for illegal zero byte TSDU ( ETSDU) send attempts.

ATTRIBUTES

WARNINGS

It is important to remember that the transport provider treats all
users of a transport endpoint as a single user. Therefore if several
processes issue concurrent t_snd() calls then the different data may
be intermixed.

Multiple sends which exceed the maximum TSDU or ETSDU size may not be
discovered by XTI. In this case an implementation-dependent error
will result, generated by the transport provider, perhaps on a
subsequent XTI call. This error may take the form of a connection
abort, a TSYSERR, a TBADDATA or a TPROTO error.

If multiple sends which exceed the maximum TSDU or ETSDU size are
detected by XTI, t_snd() fails with TBADDATA.

May 7, 1998 T_SND(3NSL)