Thanks once more! It all depends on how withMemoryRebound works.
If there is any way where it actually copies the bound memory to a separate place, then passes that copy to the closure, it would not be a good idea to write past the end of the bound memory. If withMemoryRebound is a simple cast like in C, everything would be fine (as we know there is an underlying sockaddr_storage big enough), but since we only pass the smaller size to withMemoryRebound, I'm not sure of the semantics. In the end, if it would be a simple cast, I wonder what the "capacity" parameter of withMemoryReboundis actually used for... I also "believe" it is correct but I want to know for sure :) > On 29 Dec 2016, at 16:17, Rien <r...@balancingrock.nl> wrote: > > 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 <e...@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 <r...@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@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@swift.org >>>> https://lists.swift.org/mailman/listinfo/swift-users >>> >> > _______________________________________________ swift-users mailing list swift-users@swift.org https://lists.swift.org/mailman/listinfo/swift-users
