and DH all conditional upon OPENSSL_NO_RSA.

in "types.h" so that very few headers will need to include engine.h,
generally only C files using API functions will need it (reducing
the header dependencies quite a lot).

(Some platforms need _XOPEN_SOURCE and _XOPEN_SOURCE_EXTENDED to get
the declaration, but on other platforms _XOPEN_SOURCE disables
the strdup declaration in <string.h>.)

error strings - the destroy handler functions unload the error strings so
any pending error state referring to them will not attempt to reference
them after the ENGINE has been destroyed.

being enabled or disabled (respectively) for operation. Additionally, each
ENGINE has a constructor function where it can do more 'structural' level
intialisations such as loading error strings, creating "ex_data" indices,
etc. This change introduces a handler function that gives an ENGINE a
corresponding opportunity to cleanup when the ENGINE is being destroyed. It
also adds the "get/set" API functions that control this "destroy" handler
function in an ENGINE.

defined.

(Preprocessor symbols such as _POSIX_C_SOURCE or _XOPEN_SOURCE are
supposed to disable anything not allowed by the respective
specification; I'm not sure why 'strdup' would be considered
an outlaw though.)

locking callbacks to pass to the loaded library (in addition to the
existing mem, ex_data, and err callbacks). Also change the default
implementation of the "bind_engine" function to apply those callbacks, ie.
the IMPLEMENT_DYNAMIC_BIND_FN macro.

declare their own error strings so that they can be more easily compiled as
external shared-libraries if desired. Also, each implementation has been
given canonical "dynamic" support at the base of each file and is only
built if the ENGINE_DYNAMIC_SUPPORT symbol is defined.

Also, use "void" prototypes rather than empty prototypes in engine_int.h.

This does not yet;
  (i) remove error strings when unloading,
 (ii) remove the redundant ENGINE_R_*** codes (though ENGINE_F_*** codes
      have gone), or
(iii) provide any instructions on how to build shared-library ENGINEs or
      use them.

All are on their way.

implementations to be loaded from self-contained shared-libraries. It also
provides (in engine.h) definitions and macros to help implement a
self-contained ENGINE. Version control is handled in a way whereby the
loader or loadee can veto the load depending on any objections it has with
each other's declared interface level. The way this is currently
implemented assumes a veto will only take place when one side notices the
other's interface level is too *old*. If the other side is newer, it should
be assumed the newer version knows better whether to veto the load or not.
Version checking (like other "dynamic" settings) can be controlled using
the "dynamic" ENGINE's control commands. Also, the semantics for the
loading allow a shared-library ENGINE implementation to handle differing
interface levels on the fly (eg. loading secondary shared-libraries
depending on the versions required).

Code will be added soon to the existing ENGINEs to illustrate how they can
be built as external libraries rather than building statically into
libcrypto.

NB: Applications wanting to support "dynamic"-loadable ENGINEs will need to
add support for ENGINE "control commands". See apps/engine.c for an example
of this, and use "apps/openssl engine -vvvv" to test or experiment.

See the commit log message for that for more information.

NB: X509_STORE_CTX's use of "ex_data" support was actually misimplemented
(initialisation by "memset" won't/can't/doesn't work). This fixes that but
requires that X509_STORE_CTX_init() be able to handle errors - so its
prototype has been changed to return 'int' rather than 'void'. All uses of
that function throughout the source code have been tracked down and
adjusted.

setting stack (actually, array) values in ex_data. So only increment the
global counters if the underlying CRYPTO_get_ex_new_index() call succeeds.
This change doesn't make "ex_data" right (see the comment at the head of
ex_data.c to know why), but at least makes the source code marginally less
frustrating.

NOTE: Boolean input hasn't been very well tested yet, so this part may
fail miserably.

_XOPEN_SOURCE_EXTENDED wasn't very smart...

success return, any negative number is a failure.  Make sure we check
the return value with that in mind.

Fix memory leak when RAND is used: need to cleanup
RANDs ENGINE reference in ENGINE_cleanup().

  with arbitrary arguments instead of just a string.
- Change the key loaders to take a UI_METHOD instead of a callback
  function pointer.  NOTE: this breaks binary compatibility with
  earlier versions of OpenSSL [engine].
- Addapt the nCipher code for these new conditions and add a card
  insertion callback.

PR:

_XOPEN_SOURCE.