t_snd Subroutine for X/Open Transport Interface

AIX Version 4.3 Communications Technical Reference, Volume 2

t_snd Subroutine for X/Open Transport Interface

Purpose

Send data or expedited data over a connection.

Library

X/Open Transport Interface Library (libxti.a)

Syntax

#include <xti.h>

int t_snd (
    int fd,
    void *buf,
    unsigned int nbytes,
    int *flags)

Description

The t_snd subroutine is used to send either normal or expedited data. By default, the t_snd subroutine operates in synchronous mode and may wait if flow control restrictions prevents the data from being accepted by the local transport provider at the time the call is made. However, if O_NONBLOCK is set (via the t_open subroutine or fcntl), the t_snd subroutine executes in asynchronous mode, and fails immediately if there are flow control restrictions. The process can arrange to be informed when the flow control restrictions are cleared via either the t_look subroutine or the Event Management interface.

On successful completion, the t_snd subroutine returns the number of bytes accepted by the transport provider. Normally this equals the number of bytes specified in the nbytes parameter. However, if O_NONBLOCK is set, it is possible that only part of the data is actually accepted by the transport provider. In this case, the t_snd subroutine returns a value that is less than the value of the nbytes parameter. If the value of the nbytes parameter is zero and sending of zero octets is not supported by the underlying transport service, the t_snd subroutine returns -1 with t_errno set to TBADDATA.

Parameters

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.

flags

Specifies any optional flags described below:

T_EXPEDITED

If set in the flags parameter, the data is sent as expedited data and is subject to the interpretations of the transport provider.

T_MORE

If set in the flags parameter, 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 call with the T_MORE flag set indicates that another t_snd call will follow with more data for the current 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 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 parameter on return from the t_open or t_getinfo subroutines, the T_MORE flag is not meaningful and is 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, for example, when the T_MORE flag is not set. Some transport providers also forbid zero-length TSDUs and ETSDUs. See Appendix A, ISO Transport Protocol Information for a fuller explanation.

Valid States

T_DATAXFER, T_INREL.

Return Values

On successful completion, the t_snd subroutine 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 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.

Error Codes

On failure, t_errno is set to one of the following:

TBADF	The specified file descriptor 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 a zero byte TSDU (ETSDU) or zero byte fragment of a TSDU (ETSDU) is not supported by the provider (see Appendix A, ISO Transport Protocol Information) . 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-dependent. See "Implementation Specifics".
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.
TNOTSUPPORT	This subroutine is not supported by the underlying transport provider.
TLOOK	An asynchronous event has occurred on this transport endpoint.
TOUTSTATE	The subroutine was issued in the wrong sequence on the transport endpoint referenced by the fd parameter.
TSYSERR	A system error has occurred during execution of this subroutine.
TPROTO	This error indicates that a communication problem has been detected between the X/Open Transport Interface and the transport provider for which there is no other suitable X/Open Transport Interface (t_errno).

Implementation Specifics

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 the X/Open Transport Interface. 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 the X/Open Transport Interface, t_snd fails with TBADDATA.

Related Information

The t_getinfo subroutine, t_open subroutine, t_rcv subroutine.