Inside Macintosh: Open Transport /

Chapter 3 - Endpoints / Endpoints Reference

Functions / Functions for Connection-Oriented Transaction-Based Endpoints

OTRcvReply

Reads a transaction reply sent by a connection-oriented responder.

C INTERFACE

OSStatus OTRcvReply (EndpointRef ref, TReply* reply, 
                     OTFlags* replyFlags);

C++ INTERFACE

OSStatus TEndpoint::RcvReply(TReply* reply, OTFlags* flags);

PARAMETERS

ref

The endpoint reference of the endpoint reading the reply.

reply

A pointer to a TReply structure (page 3-67) that specifies the size and location of buffers into which the function, on return, stores data, option information, and the ID of the transaction. See the description of the TReply structure for how to set this parameter when doing a no-copy receive.

replyFlags

A long bitmapped field specifying T_MORE or T_PARTIALDATA. A value of T_MORE indicates that the buffer pointed to by reply->data.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 and that the next data unit might belong to a different transaction.

DESCRIPTION

You use the OTRcvReply function to read the reply to a request that you sent using the OTSndRequest function.

If the endpoint is in asynchronous mode, the endpoint provider issues the T_REPLY event to let you know that incoming reply data is available. After you retrieve this event (using the OTLook function or your notifier function,) you must call the OTRcvReply function repeatedly to read the reply data until it returns kOTNoDataErr. The endpoint provider does not generate additional T_REPLY events until you have read the complete reply.

If a transaction has timed out awaiting reply data, the OTRcvReply 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 OTRcvReply 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 replyFlags setting. Once you determine the matching request and the appropriate reply buffer, you can call the OTRcvReply 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 OTRcvReply 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 OTRcvRequest 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 OTRcvReply 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

The request to which you are receiving a reply is defined by a previous call to the OTSndRequest function (page 3-137).

You use the TReply structure (page 3-67) to specify the size and location of buffers into which the function, on return, stores data, option information, and the ID of the transaction.

You use the OTLook function (page 3-85) to poll for asynchronous events.