t_snd(3NSL) Networking Services Library Functions t_snd(3NSL)NAMEt_snd - send data or expedited data over a connection
SYNOPSIS
#include <xti.h>
int t_snd(int fd, void *buf, unsigned int nbytes, int flags);
DESCRIPTION
This routine is part of the XTI interfaces which evolved from the TLI
interfaces. XTI represents the future evolution of these interfaces.
However, TLI interfaces are supported for compatibility. When using a
TLI routine that has the same name as an XTI routine, the tiuser.h
header file must be used. Refer to the TLI COMPATIBILITY section for
a description of differences between the two interfaces.
This function is used to send either normal or expedited data. The
argument fd identifies the local transport endpoint over which data
should be sent, buf points to the user data, nbytes specifies the num‐
ber 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 cur‐
rent TSDU (or ETSDU).
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 noth‐
ing 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(3NSL) or t_get‐
info(3NSL), the T_MORE flag is not meaningful and will
be ignored if set.
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; that is, when the T_MORE
flag is not set. Some transport providers also forbid
zero-length TSDUs and ETSDUs.
T_PUSH If set in flags, requests that the provider transmit
all data that it has accumulated but not sent. The
request is a local action on the provider and does not
affect any similarly named protocol flag (for example,
the TCP PUSH flag). This effect of setting this flag is
protocol-dependent, and it may be ignored entirely by
transport providers which do not support the use of
this feature.
Note that the communications provider is free to collect data in a send
buffer until it accumulates a sufficient amount for transmission.
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_NON‐
BLOCK is set by means of t_open(3NSL) or fcntl(2), t_snd() will exe‐
cute in asynchronous mode, and will fail immediately if there are flow
control restrictions. The process can arrange to be informed when the
flow control restrictions are cleared by means of either t_look(3NSL)
or the EM interface.
On successful completion, t_snd() returns the number of bytes (octets)
accepted by the communications provider. Normally this will equal the
number of octets specified in nbytes. However, if O_NONBLOCK is set or
the function is interrupted by a signal, it is possible that only part
of the data has actually been accepted by the communications provider.
In this case, t_snd() returns a value that is less than the value of
nbytes. If t_snd() is interrupted by a signal before it could transfer
data to the communications provider, it returns -1 with t_errno set
to TSYSERR and errno set to EINTR.
If nbytes is zero and sending of zero bytes is not supported by the
underlying communications service, t_snd() returns −1 with t_errno
set to TBADDATA.
The size of each TSDU or ETSDU must not exceed the limits of the trans‐
port provider as specified by the current values in the TSDU or ETSDU
fields in the info argument returned by t_getinfo(3NSL).
The error TLOOK is returned for asynchronous events. It is required
only for an incoming disconnect event but may be returned for other
events.
RETURN VALUES
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.
Note that if the number of bytes accepted by the communications
provider is less than the number of bytes requested, this may either
indicate that O_NONBLOCK is set and the communications provider is
blocked due to flow control, or that O_NONBLOCK is clear and the func‐
tion was interrupted by a signal.
ERRORS
On failure, t_errno is set to one of the following:
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 a zero byte TSDU (ETSDU) or zero byte
fragment of a 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 an XTI implementation to
detect such an error case is implementation-depen‐
dent. See WARNINGS, below.
TBADF The specified file descriptor does not refer to a
transport endpoint.
TBADFLAG An invalid flag was specified.
TFLOW O_NONBLOCK was set, but the flow control mechanism pre‐
vented the transport provider from accepting any data
at this time.
TLOOK An asynchronous event has occurred on this transport
endpoint.
TNOTSUPPORT This function is not supported by the underlying trans‐
port provider.
TOUTSTATE The communications endpoint referenced by fd is not in
one of the states in which a call to this function is
valid.
TPROTO This error indicates that a communication problem has
been detected between XTI and the transport provider
for which there is no other suitable XTI error
(t_errno).
TSYSERR A system error has occurred during execution of this
function.
TLI COMPATIBILITY
The XTI and TLI interface definitions have common names but use differ‐
ent header files. This, and other semantic differences between the two
interfaces are described in the subsections below.
Interface Header
The XTI interfaces use the header file, xti.h. TLI interfaces should
not use this header. They should use the header:
#include <tiuser.h>
Error Description Values
The t_errno values that can be set by the XTI interface and cannot be
set by the TLI interface are:
TPROTO
TLOOK
TBADFLAG
TOUTSTATE
The t_errno values that this routine can return under different circum‐
stances than its XTI counterpart are:
TBADDATA
In the TBADDATA error cases described above, TBADDATA is returned, only
for illegal zero byte TSDU ( ETSDU) send attempts.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│MT Level │Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOfcntl(2), t_getinfo(3NSL), t_look(3NSL), t_open(3NSL), t_rcv(3NSL),
attributes(5)WARNINGS
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, a TSY‐
SERR, a TBADDATA or a TPROTO error.
If multiple sends which exceed the maximum TSDU or ETSDU size are
detected by XTI, t_snd() fails with TBADDATA.
SunOS 5.10 7 May 1998 t_snd(3NSL)
