objective-ccore-foundationswifttoll-free-bridging

Toll-free bridging and pointer access in Swift


I am porting an App from Objective-C to Swift and I need to use the following method:

CFStreamCreatePairWithSocketToHost(alloc: CFAllocator!, host: CFString!, port: UInt32, \
readStream: CMutablePointer<Unmanaged<CFReadStream>?>, \
writeStream: CMutablePointer<Unmanaged<CFWriteStream>?>)

The old logic looks like this (which several web sites seem to agree on):

CFReadStreamRef readStream = NULL;
CFWriteStreamRef writeStream = NULL;
CFStreamCreatePairWithSocketToHost(NULL, (__bridge CFStringRef)(host), port, \
                                   &readStream, &writeStream);

NSInputStream inputStream = (__bridge_transfer NSInputStream *)readStream;
NSOutputStream outputStream = (__bridge_transfer NSOutputStream *)writeStream;

Which works fine thanks to toll-free bridging. However, ARC does not exist in "Swift-space", and the type system has changed.

How do I turn my streams into instances of

CMutablePointer<Unmanaged<CFReadStream>?>, and
CMutablePointer<Unmanaged<CFWriteStream>?>

And then convert them back into NSStream subclasses after the CFStreamCreatePairWithSocketToHost call?


Solution

  • I got it to work, here's my code: Make sure you keep a reference of the connection class somewhere :-)

    class Connection : NSObject, NSStreamDelegate {
        let serverAddress: CFString = "127.0.0.1"
        let serverPort: UInt32 = 8443
    
        private var inputStream: NSInputStream!
        private var outputStream: NSOutputStream!
    
        func connect() {
            println("connecting...")
    
            var readStream:  Unmanaged<CFReadStream>?
            var writeStream: Unmanaged<CFWriteStream>?
    
            CFStreamCreatePairWithSocketToHost(nil, self.serverAddress, self.serverPort, &readStream, &writeStream)
    
            // Documentation suggests readStream and writeStream can be assumed to
            // be non-nil. If you believe otherwise, you can test if either is nil
            // and implement whatever error-handling you wish.
    
            self.inputStream = readStream!.takeRetainedValue()
            self.outputStream = writeStream!.takeRetainedValue()
    
            self.inputStream.delegate = self
            self.outputStream.delegate = self
    
            self.inputStream.scheduleInRunLoop(NSRunLoop.currentRunLoop(), forMode: NSDefaultRunLoopMode)
            self.outputStream.scheduleInRunLoop(NSRunLoop.currentRunLoop(), forMode: NSDefaultRunLoopMode)
    
            self.inputStream.open()
            self.outputStream.open()
        }
    
        func stream(stream: NSStream, handleEvent eventCode: NSStreamEvent) {
            println("stream event")
        }
    }