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 as follows:
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: This is a meaningful parameter. This is
not a meaningful parameter. The content of the object
pointed to by y is meaningful. Specifies a file descriptor
returned by the t_open() function that identifies the
local transport endpoint where an active connection
exists. 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 are: 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 calls.
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
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 values: 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 zerobyte
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-control restrictions. 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 suitable
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),
Network Programmer's Guide
[ Back ]