t_snd -- send data or expedited data over a connection


TLI syntax

cc . . . -lnsl

#include <sys/tiuser.h>

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

XTI syntax

cc . . . -lxti

#include <xti.h>

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


The t_snd function is used to send either normal or expedited data. 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.

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 (via t_open or fcntl), t_snd executes in asynchronous mode, and fails immediately if there are flow control restrictions.

Even when there are no flow control restrictions, t_snd waits if STREAMS internal resources are not available, regardless of the state of O_NONBLOCK.

On successful completion, t_snd returns the number of bytes accepted by the transport provider. Normally this equals the number of bytes specified in nbytes. However, if O_NONBLOCK is set, it is possible that only part of the data is accepted by the transport provider. In this case, t_snd sets T_MORE for the data that was sent (see below) and returns a value less than nbytes. If nbytes is zero, no data is passed to the provider and t_snd returns zero.

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

If T_MORE is set in flags, or is set as described above, an indication is sent 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 follows with more data for the current TSDU. 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 or t_getinfo, the T_MORE flag is not meaningful and should be ignored.

The size of each TSDU or ETSDU must not exceed the limits of the transport provider as returned by t_open or t_getinfo. If the size is exceeded, a TSYSERR with system error EPROTO occurs. However, the t_snd may not fail because EPROTO errors may not be reported immediately. In this case, a subsequent call that accesses the transport endpoint fails with the associated TSYSERR.

If t_snd is issued from the T_IDLE state, the provider may silently discard the data. If t_snd is issued from any state other than T_DATAXFER, T_INREL or T_IDLE, the provider generates a TSYSERR with system error EPROTO (which may be reported in the manner described above).

Return values

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


On failure, t_errno may be set to one of the following:

Bad data was encountered with flags set to T_EXPEDITED.

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

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

The flags argument must be either T_END, T_EXPEDITED, T_MORE, or T_EXPEDITED Or'ed with T_MORE.

A disconnect or an orderly release request is occurring on the transport endpoint.

The use of the T_CLTS service type is not supported by the underlying transport provider.

The function was issued in the wrong sequence on the transport endpoint referenced by fd

A system error occurred during execution of this function.

See also

Intro(NET), t_getinfo(NET), t_open(NET), t_rcv(NET)

Standards conformance

t_snd is conformant with:

AT&T SVID Issue 3 ;
X/Open CAE Specification, Networking Services, Issue 4, 1994. ;
and Intel386 Binary Compatibility Specification, Edition 2 (iBCSe2) .

© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003