Inside Macintosh: Open Transport /

Chapter 3 - Endpoints / Endpoints Reference

Functions / Functions for Connectionless Transaction-Based Endpoints

OTRcvURequest

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

C INTERFACE

OSStatus OTRcvURequest (EndpointRef ref, TUnitRequest* req, 
                        OTFlags* flags);

C++ INTERFACE

OSStatus TEndpoint::RcvURequest(TUnitRequest* req, OTFlags* flags);

PARAMETERS

ref

The endpoint reference of the endpoint accepting the request.

req

A pointer to a TUnitRequest structure (page 3-58) that contains information about the request being received. See the description of the TUnitRequest structure for how to set this parameter when doing a no-copy receive.

flags

A long bitmapped field set by the endpoint provider that specifies whether the request is acknowledged (T_ACKNOWLEDGED) and whether there is more request data coming (T_MORE) or (T_PARTIALDATA). A value of T_MORE indicates that the buffer you have allocated 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 all flags are set.

DESCRIPTION

You use the OTRcvURequest function to read an incoming request. When the function returns, it fills in the TUnitRequest structure (referenced by the req parameter) with the address of the sender, the request data, and any association-related options pertaining to this request.

If the endpoint is in synchronous mode and is blocking, the OTRcvURequest function waits for a request to arrive. If the endpoint is in asynchronous mode or is not blocking, the OTRcvURequest function retrieves the next pending unread request or returns the kOTNoDataErr result if there are no pending requests.

If the endpoint is in asynchronous mode, the endpoint provider generates a T_REQUEST event when a request arrives. You can poll the endpoint using the OTLook function or use a notifier function to retrieve this event.

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

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 request 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 requesters and the OTRcvURequest function returns with the T_PARTIALDATA flag set, it is possible that your next call to the OTRcvURequest function might not read the rest of the request because the next data unit coming in belongs to a different request. One way to handle this situation is to use the next call to the OTRcvURequest function to determine the sequence number of the incoming request (by setting req->udata.len to 0) and then, having determined which request data is coming in, read the data into the appropriate buffer.

The provider sets the T_ACKNOWLEDGED flag if the requester has set this flag when calling the OTSndURequest function. When this flag is set and you call the OTSndUReply function, Open Transport guarantees that your reply is acknowledged by the requester. This flag is set only on the first call to the OTRcvURequest function for any given transaction.

VALID STATES

T_IDLE

SEE ALSO

To determine the maximum size of the request data, you must call the OTGetEndpointInfo function (page 3-82) and examine the etsdu field of the TEndpointInfo structure (page 3-48) that it returns.

You use the TUnitRequest structure (page 3-58) to store information about the request being received.

You can poll for the T_REQUEST event by calling the OTLook function (page 3-85).

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

To respond to a request, you use the OTSndUReply function (described next).