[swift-users] How much memory does withMemoryRebound bind

[Rien]

I used the code from http://blog.obdev.at/representing-socket-addresses-in-swift-using-enums/ in my package SwifterSockets (see github link below)

It does not answer your question exactly, but I think it is a rather better approach to sockaddr usage.

Regards,
Rien

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




> On 29 Dec 2016, at 14:27, Etan Kissling via swift-users <swift-users at swift.org> wrote:
> 
> Hi,
> 
> When calling POSIX accept, the common way is to
> sockaddr_storage addr = {0};
> sockaddr_len addrlen = 0;
> int clientFd = accept(serverFd, (sockaddr *) &addr, &addrlen);
> 
> In Swift, this translates to
> var addr = sockaddr_storage()
> var addrlen = sockaddr_len(0)
> int clientFd = withUnsafeMutablePointer(to: addr) {
>    $0.withMemoryRebound(to: sockaddr.self, capacity: 1) { addr in
>        Foundation.accept(socket, addr, &addrlen)
>    }
> }
> 
> Since sockaddr is smaller than sockaddr_storage, I wonder if this is correct.
> 
> If withMemoryRebound would be the same as the simple C cast, it would be okay.
> However, since it also requires passing the capacity, I wonder if there may be cases
> where it actually copies out the memory region, which could lead to memory corruption.
> 
> ==> How can I guarantee that withMemoryRebound binds the complete sockaddr_storage,
>       and prevent cases where only the first MemoryLayout<sockaddr>.size bytes are bound?
> 
> Thanks
> 
> Etan
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