Inside Macintosh: Open Transport /

Chapter 3 - Endpoints / Endpoints Reference

Functions / Functions for Connectionless Transaction-Based Endpoints

OTRcvUReply

Reads a reply to a request sent by a client using a connectionless transaction-
based protocol.

C INTERFACE

OSStatus OTRcvUReply (EndpointRef ref, TUnitReply* reply, 
                      OTFlags* flagPtr);

C++ INTERFACE

OSStatus TEndpoint::RcvUReply(TUnitReply* reply, OTFlags* flags);

PARAMETERS

ref

The endpoint reference of the endpoint accepting the reply.

reply

A pointer to a TUnitReply structure (page 3-60) that contains information about the reply data and the ID of the transaction. See the description of the TUnitReply structure for how to set this parameter when doing a no-copy receive.

flagPtr

A pointer to a bitmapped long that is filled in by the endpoint provider to indicate whether there is more reply data to be
read, in which case you must call the OTRcvUReply function again. A value of T_MORE indicates that the buffer pointed to
by udata.buf is too small to contain the reply. A value of T_PARTIALDATA indicates that the data unit being read does not contain the complete reply. It is possible that both flags are set.

DESCRIPTION

You use the OTRcvUReply function to read the reply to a request that you have issued using the OTSndURequest function. The reply parameter points to buffers in which the function stores the reply, the address of the responder, any options connected with this transaction, and the transaction ID for this transaction.

If the endpoint is in asynchronous mode, the provider generates a T_REPLY event to let you know that reply data has arrived. If it should happen that the reply data is sent using multiple calls to the sending function, Open Transport does not generate additional T_REPLY events. To guard against this possibility, your notifier function should call the OTRcvUReply function until it returns the kOTNoDataErr result.

If a transaction has timed out awaiting reply data, the OTRcvUReply function returns a kETIMEDOUTErr result; the sequence field of the reply parameter specifies which request has timed out.

If you have issued multiple requests, it is not possible to know ahead of time how incoming replies match your requests. You must be prepared to receive a reply to any outstanding request. One way to manage this situation is to call the OTRcvUReply function with the reply->udata.maxlen field set to 0. The rest of the information returned by the function on this first call lets you know the sequence number of the reply as well as the flagPtr setting. Once you determine the matching request and the appropriate reply buffer, you can call the OTRcvUReply function a second time to read the actual reply data. On the second and subsequent reads, Open Transport sets the reply->opt.len field to 0. It is guaranteed that once a reply has been partially read, subsequent calls to OTRcvUReply read from that same reply until all the data has been read.

If the T_MORE bit is set in the flags parameter, this means your buffer is not large enough to hold the entire reply. You must call the OTRcvURequest function again to retrieve more request data. Open Transport ignores the addr and opt fields of the reply parameter for subsequent calls to the function. The T_MORE flag is not set for the last reply packet to let you know that this is the last packet.

If the T_PARTIALDATA bit is set in the flags parameter, this means that the data you are about to read with the OTRcvUReply function does not constitute the entire reply and that you must call the function again to read more of or the rest of the reply.

If the T_MORE and the T_PARTIALDATA bits are both set, this means that the data you are about to read constitutes only part of the reply and that your buffer is too small to contain even this chunk. In this case, you must call the function again until the T_MORE flag is clear. The T_PARTIALDATA bit is set only on the first call to the function.

If you are communicating with multiple responders and if the OTRcvUReply function returns with the T_PARTIALDATA flag set, it is possible that your next call to the function might not read the rest of the reply because the next data unit coming in belongs to a different reply. One way to handle this situation is to use the next call to the OTRcvReply function to determine the sequence number of the incoming reply (by setting req->udata.maxlen to 0) and then, having determined which reply data is coming in, read the data into the appropriate buffer.

VALID STATES

T_IDLE

SEE ALSO

You use the OTSndURequest function (page 3-107) to send a request.

For information on how to use this function with the AppleTalk ATP protocol, see page 14-10 in the ATP chapter.

You use the TUnitReply structure (page 3-60) to store information about the reply data and the ID of the transaction.