t_snd(3N) UNIX System V(Networking Support Utilities) t_snd(3N)
NAME
tsnd - send data or expedited data over a connection
SYNOPSIS
#include <tiuser.h>
int tsnd (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, tsnd 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 ONDELAY or
ONONBLOCK is set (via topen or fcntl), tsnd will execute in
asynchronous mode, and will fail immediately if there are flow control
restrictions.
Even when there are no flow control restrictions, tsnd will wait if
STREAMS internal resources are not available, regardless of the state of
ONDELAY or ONONBLOCK.
On successful completion, tsnd returns the number of bytes accepted by
the transport provider. Normally this will equal the number of bytes
specified in nbytes. However, if ONDELAY or ONONBLOCK is set, it is
possible that only part of the data will be accepted by the transport
provider. In this case, tsnd will set TMORE for the data that was sent
(see below) and will return a value less than nbytes. If nbytes is zero
and sending of zero bytes is not supported by the underlying transport
provider, tsnd() will return -1 with terrno set to TBADDATA. A return
value of zero indicates that the request to send a zero-length data
message was sent to the provider.
If TEXPEDITED is set in flags, the data will be sent as expedited data,
and will be subject to the interpretations of the transport provider.
If TMORE 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 tsnd calls. Each tsnd with the TMORE flag set
indicates that another tsnd will follow with more data for the current
TSDU. The end of the TSDU (or ETSDU) is identified by a tsnd call with
the TMORE flag not set. Use of TMORE 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 topen or tgetinfo, the TMORE flag is not
meaningful and should be ignored.
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t_snd(3N) UNIX System V(Networking Support Utilities) t_snd(3N)
The size of each TSDU or ETSDU must not exceed the limits of the
transport provider as returned by topen or tgetinfo. If the size is
exceeded, a TSYSERR with system error EPROTO will occur. However, the
tsnd 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 tsnd is issued from the TIDLE state, the provider may silently
discard the data. If tsnd is issued from any state other than
TDATAXFER, TINREL or TIDLE, the provider will generate a TSYSERR with
system error EPROTO (which may be reported in the manner described
above).
On failure, terrno may be set to one of the following:
TBADF The specified file descriptor does not refer to a
transport endpoint.
TFLOW ONDELAY or ONONBLOCK was set, but the flow control
mechanism prevented the transport provider 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 function.
TBADDATA nbytes is zero and sending zero bytes is not
supported by the transport provider.
NOTES
The tsnd routine does not look for a disconnect indication (showing that
the connection was broken) before passing data to the provider.
SEE ALSO
topen(3N), trcv(3N)
Programmer's Guide: Networking Interfaces
DIAGNOSTICS
On successful completion, tsnd returns the number of bytes accepted by
the transport provider, and it returns -1 on failure and terrno is set
to indicate the error.
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