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t_snd - Send normal data or expedited data over a connection
int flags );
XTI Library (libxti.a)
Interfaces documented on this reference page conform to industry standards
t_snd(): XNS4.0, XNS5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
The following table summarizes the relevance of input and output parameters
before and after t_snd() is called:
Parameters Before Call After Call
fd y n
buf y(y) n
nbytes y n
flags y n
Notes to Table:
y This is a meaningful parameter.
n This is not a meaningful parameter.
(y) The content of the object pointed to by y is meaningful.
fd Specifies a file descriptor returned by the t_open() function that
identifies the local transport endpoint where an active connection
buf Points to the data buffer from which data is to be sent.
Specifies the length in bytes of the send data buffer contents pointed
to by the buf parameter.
Points to an integer whose bits specify certain optional information.
Corresponding values and symbolic names for these option bits are
defined in the xti.h include file. Flags specified by this function
When set, this bit notifies the transport provider that sent data
is a fragment of a Transport Service Data Unit (TSDU) or Expedited
Transport Service Data Unit (ETSDU), and that more data will be
sent on the same TSDU or ETSDU via the t_snd() function. The rest
of the TSDU or ETSDU can be sent through further t_snd() function
Each time the T_MORE option is set, another t_snd() call follows so
that additional parts of the TSDUs or ETSDUs can be sent. When the
final piece is sent, this option bit is set to a value of 0 (zero).
When the transport provider does not support TSDU or ETSDU data
exchanges (refer to the t_open() and t_getinfo() functions) the
state of this option bit is meaningless.
Sending 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 option is not set. Some transport providers also
forbid zero-length TSDUs and ETSDUs.
When set, this bit notifies the transport provider that expedited
data is sent. When the value of ETSDU data exceeds the value
specified by nbytes parameter, this option bit and the T_MORE
option bit should be set prior to the initial t_snd() call.
Subsequent t_snd() calls used to send pieces of ETSDU must have
both these option bits set. When the final ETSDU is sent, the
T_MORE option bit is set to a value of 0 (zero).
The t_snd() function is an XTI connection-oriented service function that is
used to send normal or expedited data. The transport endpoint through which
normal Transport Service Data Unit (TSDU) data or special Expedited TSDU
(ETSDU) data is sent is specified by a file descriptor previously returned
by the t_open() function.
The size of each TSDU or ETSDU must not exceed the size limits specified by
info->tsdu or info->etsdu, respectively, returned by the t_open() or
t_getinfo() functions. Failure to comply with specified size constraints
results in return of a [TSYSERR] protocol error. By default, the t_snd()
function executes in the synchronous operating mode. In the synchronous
operating mode t_snd() waits for data to be accepted by the transport
provider, before returning control to the calling transport user.
When the transport endpoint specified by the file descriptor has been
opened with the O_NONBLOCK flag set in the t_open() or fcntl() function,
the t_snd() function executes in asynchronous mode. When data cannot be
immediately accepted because flow control restrictions apply, control is
immediately returned to the caller.
When the t_snd() function executes successfully, the number of bytes
accepted by the transport provider is returned. It is possible that only
part of the data may be accepted by a transport provider. When only
partial data is accepted, the returned value is less than the number of
bytes sent. If the nbytes parameter is specified as 0 (zero), and the
underlying transport service does not support the sending of 0 octets,
t_errno is set to [TBADDATA] and -1 is returned.
In asynchronous mode, when the number of bytes accepted by the transport
provider is less than the number of bytes sent, the transport provider may
be blocked because of flow-control restrictions.
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 ERSDU size may not be
discovered by XTI. In this case, an implementation-dependent error will
result, which may take the form of a connection abort, or a [TSYSERR],
[TBADDATA], or a [TPROTO] error.
If XTI detects multiple sends that exceed the maximum TSDU or ETSDU size,
t_snd() fails with the error [TBADDATA].
Upon successful completion, the t_snd() function returns the number of
bytes of data accepted by the transport provider. Otherwise, -1 is returned
and t_errno is set to indicate the error.
If the t_snd() function fails, t_errno may be set to one of the following
File descriptor fd does not refer to a valid transport endpoint.
Illegal amount of data:
· A single send was attempted specifying a TSDU or ETSDU, or a
fragment TSDU or ETSDU, greater than that specified by the current
values of the TSDU or ETSDU fields in the info argument.
· A send of a zero-byte TSDU or ETSDU, or a zero-byte fragment of a
TSDU or ETSDU, is not supported by the provider.
· Multiple sends were attempted, which resulted in a TSDU or ETSDU
larger than that specified by the current values of the TSDU or
ETSDU fields in the info argument. The ability to detect this
error is implementation dependent.
An invalid flags value was specified.
Asynchronous mode is indicated because O_NONBLOCK was set, but no data
can currently be accepted by the transport provider because of flow-
An asynchronous event occurred on this transport endpoint.
The t_snd() function was issued in the wrong sequence on the transport
endpoint referenced by the fd parameter.
A system error occurred during execution of the t_snd() function. A
protocol error may not cause t_snd() to fail until a subsequent access
of the transport endpoint is made.
This function is not supported by the underlying transport provider.
This error indicates that a communication problem has been detected
between XTI and the transport provider for which there is no other
The t_snd() function can be called only in the T_DATAXFER and T_INREL
transport provider states.
Functions: fcntl(2), t_getinfo(3), t_look(3), t_open(3), t_optmgmt(3),
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