|Networking Services Library Functions
t_snd - send data or expedited data over a connection
#include <xti.h> int t_snd(int fd, void *buf, unsigned int nbytes, int flags);
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 number of bytes of user data to be sent, and flags specifies any optional flags described below:
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 argument on return from t_open(3NSL) or t_getinfo(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.
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_NONBLOCK is set by means of t_open(3NSL) or fcntl(2), 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 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 transport 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.
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 function was interrupted by a signal.
On failure, t_errno is set to one of the following:
The XTI and TLI interface definitions have common names but use different header files. This, and other semantic differences between the two interfaces are described in the subsections below.
The XTI interfaces use the header file, xti.h.
TLI interfaces should not use this header. They should use the
The t_errno values that can be set by the XTI
interface and cannot be set by the TLI interface are:
The t_errno values that this routine can return under
different circumstances than its XTI counterpart are:
In the TBADDATA error cases described above, TBADDATA is returned, only for illegal zero byte TSDU ( ETSDU) send attempts.
See attributes(7) for descriptions of the following attributes:
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.
|May 7, 1998