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Technical Standard: Networking Services (XNS), Issue 5.2 Draft 2.0
Copyright © 1999 The Open Group


t_rcv - receive data or expedited data sent over a connection


#include <xti.h>

int t_rcv(int fd, void *buf, unsigned int nbytes, int *flags);


Parameters Before call After call

fd x /
buf x (x)
nbytes x /
flags / x

This function receives either normal or expedited data. The argument fd identifies the local transport endpoint through which data will arrive, buf points to a receive buffer where user data will be placed, and nbytes specifies the size of the receive buffer. The argument flags may be set on return from t_rcv() and specifies optional flags as described below.

By default, t_rcv() operates in synchronous mode and will wait for data to arrive if none is currently available. However, if O_NONBLOCK is set (via t_open() or fcntl()), t_rcv() will execute in asynchronous mode and will fail if no data is available. (See [TNODATA] below.)

On return from the call, if T_MORE is set in flags, this indicates that there is more data, and the current transport service data unit (TSDU) or expedited transport service data unit (ETSDU) must be received in multiple t_rcv() calls. In the asynchronous mode, or under unusual conditions (for example, the arrival of a signal or T_EXDATA event), the T_MORE flag may be set on return from the t_rcv() call even when the number of bytes received is less than the size of the receive buffer specified. Each t_rcv() with the T_MORE flag set indicates that another t_rcv() must follow to get more data for the current TSDU. The end of the TSDU is identified by the return of a t_rcv() call with the T_MORE flag not set. If the transport provider does not support the concept of a TSDU as indicated in the info argument on return from t_open() or t_getinfo(), the T_MORE flag is not meaningful and should be ignored. If nbytes is greater than zero on the call to t_rcv(), t_rcv() will return 0 only if the end of a TSDU is being returned to the user.

On return, the data is expedited if T_EXPEDITED is set in flags. If T_MORE is also set, it indicates that the number of expedited bytes exceeded nbytes, a signal has interrupted the call, or that an entire ETSDU was not available (only for transport protocols that support fragmentation of ETSDUs). The rest of the ETSDU will be returned by subsequent calls to t_rcv() which will return with T_EXPEDITED set in flags. The end of the ETSDU is identified by the return of a t_rcv() call with T_EXPEDITED set and T_MORE cleared. If the entire ETSDU is not available it is possible for normal data fragments to be returned between the initial and final fragments of an ETSDU.

If a signal arrives, t_rcv() returns, giving the user any data currently available. If no data is available, t_rcv() returns -1, sets t_errno to [TSYSERR] and errno to [EINTR]. If some data is available, t_rcv() returns the number of bytes received and T_MORE is set in flags.

In synchronous mode, the only way for the user to be notified of the arrival of normal or expedited data is to issue this function or check for the T_DATA or T_EXDATA events using the t_look() function. Additionally, the process can arrange to be notified via the EM interface.




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

The specified file descriptor does not refer to a transport endpoint.

An asynchronous event has occurred on this transport endpoint and requires immediate attention.

O_NONBLOCK was set, but no data is currently available from the transport provider.

This function is not supported by the underlying transport provider.

The communications endpoint referenced by fd is not in one of the states in which a call to this function is valid.

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).

A system error has occurred during execution of this function.


On successful completion, t_rcv() returns the number of bytes received. Otherwise, it returns -1 on failure and t_errno is set to indicate the error.


fcntl(), t_getinfo(), t_look(), t_open(), t_snd().


Issue 4

The SYNOPSIS section is placed in the form of a standard C function prototype.

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