t_snd(3) t_snd(3)
NAME [Toc] [Back]
t_snd() - send data or expedited data over a connection
SYNOPSIS [Toc] [Back]
#include <xti.h> /* for X/OPEN Transport Interface - XTI */
/* or */
#include <tiuser.h> /* for Transport Layer Interface - TLI */
int t_snd (fd, buf, nbytes, flags);
int fd;
char *buf;
unsigned nbytes;
int flags;
DESCRIPTION [Toc] [Back]
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:
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. 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 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,
i.e. when the T_MORE flag is not set. Some transport providers also
forbid zero-length TSDUs and ETSDUs.
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
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t_snd(3) t_snd(3)
O_NONBLOCK is set (via t_open() or fcntl()), t_snd() will execute in
asynchronous mode, and will fail immediately if there are flow control
restrictions. For XTI only, the process can arrange to be informed
when the flow control restrictions are cleared via t_look().
t_snd() will wait if STREAMS internal resources are not available,
even if O_NONBLOCK is set. O_NONBLOCK non-blocking behavior applies
only to flow control conditions.
On successful completion, t_snd() returns the number of bytes accepted
by the transport provider. In synchronous mode, this will equal the
number of bytes specified in nbytes. However, if O_NONBLOCK
(asynchronous mode) is set, it is possible that only part of the data
will actually be accepted by the transport provider. In this case,
t_snd() will set T_MORE for the data that can be accepted by the
provider, and return a value that is less than the value of nbytes.
If nbytes is zero and sending of zero octets is not supported by the
underlying transport service, t_snd() will return -1 with t_errno set
to [TBADDATA].
The size of each TSDU or ETSDU must not exceed the limits of the
transport provider as returned in the TSDU or ETSDU fields of the info
argument of t_open() or t_getinfo(). Failure to comply will result in
a protocol error. (See [TSYSERR] below.)
For XTI only, the error [TLOOK] may be returned to inform the process
that an event (e.g., a disconnect) has occurred.
For TLI only, if the transport endpoint is in any state but T_DATAXFER
or T_INREL, the transport provider will set t_errno to [TSYSERR] and
set the system errno to [EPROTO].
Thread-Safeness [Toc] [Back]
The t_snd() function is safe to be called by multithreaded
applications, and it is thread-safe for both POSIX Threads and DCE
User Threads. It has a cancellation point. It is neither asynccancel
safe nor async-signal safe. Finally, it is not fork-safe.
Caveats [Toc] [Back]
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, [TSYSERR], [TBADDATA], or a [TPROTO].
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t_snd(3) t_snd(3)
If multiple sends which exceed the maximum TSDU or ETSDU size are
detected by XTI, t_snd() fails with [TBADDATA].
RETURN VALUE [Toc] [Back]
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.
ERRORS [Toc] [Back]
On failure, t_errno is set to one of the following:
[TBADF] The specified identifier does not refer to a
transport endpoint.
[TBADDATA] Illegal amount of data:
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.
A send of zero byte TSDU (ETSDU) or zero byte
fragment of TSDU (ETSDU) is not supported by the
provider.
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 XTI to catch such an
error case is implementation-dependent.
[TBADFLAG] An invalid flag was specified.
[TFLOW] O_NONBLOCK was set, but the flow control mechanism
prevented the transport provider from accepting
all or part of the data at this time.
[TLOOK] An asynchronous event has occurred on this
transport endpoint and requires immediate
attention.
[TNOTSUPPORT] This function is not supported by the underlying
transport provider.
[TOUTSTATE] The function was issued in the wrong sequence on
the endpoint referenced by fd.
[TSYSERR] A system error has occurred during execution of
this function.
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t_snd(3) t_snd(3)
[TPROTO] (XTI only) This error indicates that a
communication problem has been detected between
XTI and the transport provider for which there is
no other suitable XTI (t_errno).
SEE ALSO [Toc] [Back]
t_getinfo(3), t_open(3), t_rcv(3).
STANDARDS CONFORMANCE [Toc] [Back]
t_snd(): SVID2, XPG3, XPG4
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