t_rcv(3)

DESCRIPTION

The t_rcv() function receives either normal or expedited data. fd identifies the local transport endpoint through which data will arrive. buf points to a receive buffer where user data will be placed. nbytes specifies the size of the receive buffer. 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. Thus, 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, 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 immediately 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 returned is expedited data if T_EXPEDITED is set in flags. If the number of bytes of expedited data exceeds nbytes, t_rcv() will set T_EXPEDITED and T_MORE on return from the initial call. Subsequent calls to retrieve the remaining ETSDU will have T_EXPEDITED set on return. The end of the ETSDU is identified by the return of a t_rcv() call with the T_MORE flag not set.

If expedited data arrives after part of a TSDU has been retrieved, receipt of the remainder of the TSDU will be suspended until the ETSDU has been processed. Only after the full ETSDU has been retrieved (T_MORE not set) will the remainder of the TSDU be available to the user.

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.

XTI Internet Protocol-specific Information

The T_MORE flag should be ignored if normal data is delivered. If a byte in the data stream is pointed to by the TCP urgent pointer, as many bytes as possible preceding this marked byte and the marked byte itself are denoted as urgent data and are received with the T_EXPEDITED flag set. If the buffer supplied by the user is too small to hold all urgent data, the T_MORE flag will be set, indicating that urgent data still remains to be read. Note that the number of bytes received with the T_EXPEDITED flag set is not necessarily equal to the number of bytes sent by the peer user with T_EXPEDITED flag set.

RETURN VALUE

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

ERRORS

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

SEE ALSO

fcntl(2), t_getinfo(3), t_look(3), t_open(3), t_snd(3), thread_safety(5).

STANDARDS CONFORMANCE

t_rcv(): SVID2, XPG3, XPG4