[swift-users] Casting function pointers

[Rien]

Thank Joe,

A first attempt was not successful, I will try again in a few days.

For now I have put in a work around where I put glue-code into the openSSL library itself. I don’t like that solution, but it works.

Regards,
Rien

Site: http://balancingrock.nl
Blog: http://swiftrien.blogspot.com
Github: http://github.com/Balancingrock
Project: http://swiftfire.nl





> On 25 Jan 2017, at 19:37, Joe Groff <jgroff at apple.com> wrote:
> 
> 
>> On Jan 25, 2017, at 1:23 AM, Rien via swift-users <swift-users at swift.org> wrote:
>> 
>> I have a case where a callback has the following signature:
>> 
>> @convention(c) (_ ssl: OpaquePointer?, _ num: UnsafeMutablePointer<Int32>?, _ arg: UnsafeMutableRawPointer?) -> Int32
>> 
>> But to install this callback I have to use a c-function with this signature:
>> 
>> SSL_CTX_callback_ctrl (OpaquePointer!, Int32, (() -> Void)! )
>> 
>> Is it possible to cast the first function to the second? If so, how?
> 
> I think your best bet would be to write the shim closure yourself. Is `num` a pointer to the value you're supposed to receive from SSL_CTX_callback_ctrl? Is the `arg` really a function pointer? In that case, something like this might work:
> 
> func callback(_ ssl: OpaquePointer?, _ num: UnsafeMutablePointer<Int32>?, _ arg: UnsafeMutableRawPointer?) -> Int32
> 
> let shimCallback: SSL_CTX_callback_ctrl = { ctx, cmd, fp in
>  var cmdNum = cmd
>  callback(ctx, &cmdNum, unsafeBitCast(fp, to: UnsafeMutableRawPointer?.self))
> }
> 
> -Joe