[swift-users] How much memory does withMemoryRebound bind

[Rien]

Ah, ok.

In that case, I believe it is correct because sockaddr_storage is in fact big enough to hold either the IPv4 or IPv6 structure.
When bits go unused, that causes no harm. And when “addr” goes out of scope, it will be completely deallocated, so no memory leak either.

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 15:52, Etan Kissling <etan at scriptreactor.com> wrote:
> 
> I meant the question in a more generalized sense. 
> The sockaddr example is just one that is easily understandable :-)
> 
> Thanks for the link though, interesting read!
> 
>> On 29 Dec 2016, at 14:47, Rien <Rien at Balancingrock.nl> wrote:
>> 
>> 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
>>> _______________________________________________
>>> swift-users mailing list
>>> swift-users at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-users
>> 
>