Re: Modifying Emacs to use the Mac OS X Keychain Services

[Ted Zlatanov <tzz@lifelogs.com>]

On Tue, 14 Jun 2011 21:15:18 -0500 Ben Key <bkey76@gmail.com> wrote: 

BK> Stefan Monnier wrote:
>> No, a simple type cast won't do.  If the Lisp_Object is fully under your
>> control (so you always know you're the one who built it and never need
>> to check what kind of Lisp_Object it is), you can use
>> a Lisp_Misc_Save_value.  "grep -i save_value src/*.[ch]" should get
>> you started.

BK> The Lisp_Object is not always under my control.

Why not?  You're the only one providing ns-keychain-* functions.

I'm no expert on the Emacs internals, but I think you can do the
following:

The Lisp_Misc_Save_Value holds a void pointer and an integer.  Just
provide convenience functions for yourself that take a
Lisp_Misc_Save_Value and set the pointer to the SecKeychainRef or
extract it back out.  Use the `SAVE_VALUEP' and `XSAVE_VALUE' macros.

Then make a Lisp list of Lisp_Misc_Save_Value and that's your keychain
reference list.  Make the head of the Lisp list a static symbol and
GC-protect it (see gnutls.c, for instance, on how to intern a symbol and
use `staticpro' on it in the syms_of_gnutls function).  Emacs won't GC
the list then.

BK> Since the SecKeychainRef object will need to pass the boundary
BK> between internal Emacs code and Lisp code it cannot be considered to
BK> be always under my control.

Trust `staticpro' :)

BK> The problem is that I am not certain how to return a SecKeychainRef
BK> object from ns-keychain-open,  ns-keychain-create, and
BK> ns-keychain-create-or-open so that they are callable from Lisp.  Any
BK> suggestions are welcome.

I would return it as a Lisp_Misc_Save_Value and set a :ns-keychain-name
property on the value to get the keychain name (ditto for any other
keychain properties you want to preserve).

Ted