T_SND(3N) INTERACTIVE UNIX System T_SND(3N)
NAME
t_snd - send data or expedited data over a connection
SYNOPSIS
#include <tiuser.h>
int t_snd(fd, buf, nbytes, flags)
int fd;
char *buf;
unsigned nbytes;
int flags;
DESCRIPTION
This 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_NDELAY is set (via t_open or
fcntl), t_snd will execute in asynchronous mode, and will
fail immediately if there are flow control restrictions.
Even when there are no flow control restrictions, t_snd will
wait if STREAMS internal resources are not available,
regardless of the state of O_NDELAY.
On successful completion, t_snd returns the number of bytes
accepted by the transport provider. Normally this will
equal the number of bytes specified in nbytes. However, if
O_NDELAY is set, it is possible that only part of the data
will be accepted by the transport provider. In this case,
t_snd will set T_MORE for the data that was sent (see below)
and will return a value less than nbytes. If nbytes is
zero, no data will be passed to the provider and t_snd will
return zero.
If T_EXPEDITED is set in flags, the data will be sent as
expedited data, and will be 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 tran-
sport service data unit (TSDU) or expedited transport ser-
vice 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. 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
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T_SND(3N) INTERACTIVE UNIX System T_SND(3N)
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
will occur. 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 will
fail 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
will generate a TSYSERR with system error EPROTO (which may
be reported in the manner described above).
On failure, t_errno may be set to one of the following:
[TBADF] The specified file descriptor does not
refer to a transport endpoint.
[TFLOW] O_NDELAY was set, but the flow control
mechanism prevented the transport pro-
vider from accepting data at this time.
[TNOTSUPPORT] This function is not supported by the
underlying transport provider.
[TSYSERR] A system error [see intro(2)] has been
detected during execution of this func-
tion.
SEE ALSO
t_open(3N), t_rcv(3N).
Programmer's Guide.
DIAGNOSTICS
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.
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