CAP note: last revision April 1, 1987

UNIX Appletalk Transport Protocol (ATP) Implementation notes

Last revision: April 1, 1987

Design document: Inside Appletalk, June 1986.

The CAP ATP is fairly complete and follows the protocol definition
fairly closely.  The programmer's interface is as close to that of
Inside MacIntosh as could be expected.  The differences are:
	- there is no facility for an ATPAddResponse
	- ATPSndRequest will accept a socket number in atpsocket
	  instead of generating some internal socket unless zero is
	  passed.  (note: this facility is suggested by in Inside
	  Appletalk).  Furthmore, any fork using ATPSndRequest will
	  open a new socket if the passed atpsocket is zero.
	- the flags atpXO and atpEOM in the AppleBus record are
	  renamed to fatpXO and fatpEOM.

In addition, a special interface for protocol implementors has been
added.  All implemented routines (except the cancel routines) have a
"call back" version.  The arguments are the same as the standard
version of the call except no async flag is passed (it is assumed to
be asynchronous) and this argument is replaced by the address of the
callback routine and a unsigned long integer.  When the routine is
called back, it is passed the address of the applebus record and the
unsigned integer.


The following documents return codes which are not as documented by
Apple in Inside MacIntosh.

ATPSndReq
	atplenerr => reqcount too big or bad rspbdsptr
	toomanyskts => can't open socket for request
	badAtpSkt => final net write failed - probably bad write
	reqFailed => timeout
	tooManyReqs => should never happen
In the BDS, we pass buffSize to encode length of the various BDS
buffers.  If a datasize is larger than buffSize for any element of the
BDS, then this simply means the remote sent more data than the buffer
size.  Varying protocols will handle this event differently.

ATPOpenSocket
	Always returns tooManySkts if DDPOpenSocket fails...

ATPCloseSocket
	Always ignors DDPCloseSocket errors

ATPGetRequest
	noDataArea - means can't startup request

ATPSndRsp
	badBuffNum - really means that we couldn't find the specified
		request to respond to..