InputStreamGenerator.swift

struct InputStreamGenerator : Generator {
    var inputStream : NSInputStream
    var chunkSize : Int

    init(inputStream : NSInputStream, chunkSize : Int) {
        self.inputStream = inputStream
        self.chunkSize = chunkSize
    }
    
    func next() -> SequenceOf<UInt8>? {
        var buffer = UInt8[](count: chunkSize, repeatedValue: 0)
        println("performing read of \(chunkSize) bytes")
        var length = inputStream.read(&buffer, maxLength: chunkSize)
        
        if (length > 0) {
            
            // Split to separate lines to point out the Range and Slice types
            // Hopefully there is sugar i'm not aware of for slicing
            let range = Range<Int>(start: 0, end: length)
            let slice : Slice<UInt8> = buffer[range]
            let sequenceOf = SequenceOf<UInt8>(slice)
            return Optional.Some(sequenceOf)
        } else {
            return Optional.None
        }
    }
    
}

struct InputStreamSequence : Sequence {
    var inputStream : NSInputStream
    var chunkSize : Int
    
    init(inputStream : NSInputStream, chunkSize : Int) {
        self.inputStream = inputStream
        self.chunkSize = chunkSize
    }
    
    func generate() -> InputStreamGenerator  {
        return InputStreamGenerator(inputStream: self.inputStream, chunkSize: self.chunkSize)
    }
}

extension NSInputStream : Sequence {
    typealias GeneratorType = GeneratorOf<SequenceOf<UInt8>>

    func sequenceWithReadLength(chunkSize: Int) -> SequenceOf<SequenceOf<UInt8>> {
        return SequenceOf<SequenceOf<UInt8>>(InputStreamSequence(inputStream: self, chunkSize: chunkSize))
    }
    
    func generate() -> GeneratorOf<SequenceOf<UInt8>> {
        return self.sequenceWithReadLength(4096).generate()
    }
}


// basic usage
var data : NSData = "Are we not drawn onward to new era?".dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: true)
var stream : NSInputStream = NSInputStream(data: data)
stream.scheduleInRunLoop(NSRunLoop.currentRunLoop(), forMode: NSDefaultRunLoopMode)
stream.open()


for chunk : SequenceOf<UInt8> in stream.sequenceWithReadLength(2) {
    for byte in chunk {
        println(byte)
    }
}