t_snd() — Send data or expedited data over a connection

Standards

Standards / Extensions C or C++ Dependencies
XPG4.2 both  

Format

#define _XOPEN_SOURCE_EXTENDED 1
#include <xti.h>

int t_snd(int fd, char *buf, unsigned int nbytes, int flags);

General description

Sends 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 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
Since the TCP transport provider does not support the concept of a TSDU, the T_MORE flag is not meaningful and will be ignored if set.

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_NONBLOCK is set (using t_open() or fcntl() ), t_snd() will execute 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 using either t_look() or select/poll.

If successful, t_snd() returns the number of bytes accepted by the transport provider. Normally this will equal the number of bytes specified in nbytes. However, if O_NONBLOCK 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 return a value that is less than the value of nbytes.

The size of each TSDU or ETSDU must not exceed the limits of the transport provider as specified by the current values in the TSDU or ETSDU fields in the info argument returned by t_getinfo() . The error TLOOK may be returned to inform the process that an event (for example, a disconnect) has occurred.

Valid states: T_DATAXFER

Returned value

If successful, t_snd() returns the number of bytes accepted by the transport provider.

Note that in asynchronous mode, if the number of bytes accepted by the transport provider is less than the number of bytes requested, this may indicate that the transport provider is blocked due to flow control.

If unsuccessful, t_snd() returns -1 and sets errno to one of the following values:
Error Code
Description
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.
  • 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
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 prevented 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 transport provider.
TOUTSTATE
The function was issued in the wrong sequence on the transport endpoint referenced by fd.
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 (t_errno).
TSYSERR
A system error has occurred during execution of this function.

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 TSYSERR, 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.

Related information

Parent topic: Library functions