[Mono-list] Catching C-callbacks through InteropServices

[Simon Ask Ulsnes]

Hi there!
I'm writing a GnuPG interface for Mono/.NET using GPGME (GnuPG Made 
Easy, which is the C API applications use for connecting with gpg).

So far, it works fine, I can retrieve keys and encrypt/sign. However, 
the GPGME API is constructed in such a way that in order to retrieve a 
passphrase for use with decryption, you have to give it a callback 
function returning the passphrase as a const char*.

What I would do is to make a property in my GnuPGEngine class (which 
manages communication with the C layer through InteropServices) which 
will then be given to the real GnuPG engine (a GpgmeCtx, which means a 
GPGME Context object) through an internal callback.

How is this best done?

The API syntax in C for setting the callback function for the context is:
gpgme_set_passphrase(ctx, &get_passphrase, NULL);

where get_passphrase:
static const char* get_passphrase(void *HOOK, const char *DESC, void 
**R_HD);

With the above, the get_passphrase function never gets called. What to do?

- Simon