Legacy Document

Inside Macintosh: Networking /

Chapter 6 - AppleTalk Transaction Protocol (ATP) / ATP Reference

Routines / Responding to Requests

PSendResponse

The PSendResponse function sends the response message to the requester.

FUNCTION PSendResponse (thePBPtr: ATPPBPtr; async: Boolean): OSErr;

thePBPtr

A pointer to an ATP parameter block.

async

A Boolean that indicates whether the function should be executed asynchronously or synchronously. Specify TRUE for asynchronous execution.

-->	ioCompletion	ProcPtr	A pointer to a completion routine.
<--	ioResult	OSErr	The function result.
-->	userData	LongInt	Four bytes of user data.
-->	csCode	Integer	Always sendResponse for this function.
-->	atpSocket	Byte	The socket number.
-->	atpFlags	Byte	The control information.
-->	addrBlock	AddrBlock	The destination socket address.
-->	bdsPointer	Ptr	A pointer to the response BDS.
-->	numOfBuffs	Byte	The number of response packets to be sent.
-->	bdsSize	Byte	The BDS size in elements.
-->	transID	Integer	The transaction ID.

Field Description

userData

Four bytes of user data that are sent in the header of the message. If the response was part of an exactly-once transaction, this field contains the user bytes from the TRel packet.

atpSocket

The number of the socket that is sending the response.

atpFlags

A control information field whose bits, numbered 0-7, are used
as flags.

To signal that this packet is the last packet in the transaction's response message when the number of responses is less than expected, set the end-of-message (atpEOMvalue) bit (bit 4).

ATP sets the send-transmission-status (atpSTSvalue) bit (bit 3) to force the requester to retransmit a request immediately, when this
is necessary.

To direct ATP to use DDP's checksum feature, set the send checksum (atpSendChkvalue) bit (bit 0) of this flag.

addrBlock

The AppleTalk internet socket address of the socket to which the response is to be sent.

bdsPointer

A pointer to the response buffer data structure (BDS) that contains the response data.

numOfBuffs

The number of response packets to be sent.

bdsSize

The number of elements in the buffer data structure (BDS).

transID

The transaction ID of the request for which this response is meant.

DESCRIPTION

You call PSendResponse when you receive a request, and after you have created a response message. The PSendResponse function sends the data to the socket whose address you specify; this is the address of the requester socket. If you cannot or do not want to send the entire response at one time, you can call PSendResponse to send the first part of it, then call PAddResponse later to send the remainder of the response.

To signal the requester socket that you are sending fewer response packets than it expects to receive, you must set the end-of-message flag (bit 4) of the atpFlags parameter.

For each call to the PSendResponse function that is part of an exactly-once (XO) transaction, ATP maintains a timer, called the release timer. If the timer expires before
the transaction is completed, that is, before the socket receives the transaction release packet, ATP completes the PSendResponse function. Before AppleTalk Phase 2, the release timer was always set to 30 seconds. The PSendRequest or the PNSendRequest function can set the release timer for the responder to a different value. For more information about sending a response, see "Responding to Requests" beginning on page 6-16.

SPECIAL CONSIDERATIONS

During exactly-once transactions, PSendResponse doesn't complete until either a TRel packet is received from the socket that made the request or the retry count is exceeded.

ASSEMBLY-LANGUAGE INFORMATION

To execute the PSendResponse function from assembly language, call the _Control trap macro with a value of sendResponse in the csCode field of the parameter block. To execute this function from assembly language, you must also specify the .ATP driver reference number.

noErr	0	No error
badATPSkt	-1099	Bad responding socket
badBuffNum	-1100	Sequence number out of range
noRelErr	-1101	No release received
noDataArea	-1104	Too many outstanding ATP calls

RESULT CODES

SEE ALSO

See the chapter "Introduction to AppleTalk" in this book for a description of the AppleTalk internet socket address structure.

For a description of the possible release timer values that PSendRequest or PNSendRequest can set, see either the PSendRequest function on page 6-24
or the PNSendRequest function on page 6-27.