Read bytes into a Swift String

I have a binary file test.data containing the following data:

01 E6 B5 8B E8 AF 95 02

The first byte is just for example a sequence number 01. The next 6 bytes are two UTF8 Chinese characters "测试".Then the 8th byte is again another sequence number 02.

As I know the UTF8 is variable length (1-4 bytes). Please refer to this post.

I'm using the following code to read Int32 and Byte(UInt8):

extension NSInputStream
{
    func readInt32() -> Int
    {
        var readBuffer = Array<UInt8>(count:sizeof(Int32), repeatedValue: 0)

        var numberOfBytesRead = self.read(&readBuffer, maxLength: readBuffer.count)

        return Int(readBuffer[0]) << 24 |
            Int(readBuffer[1]) << 16 |
            Int(readBuffer[2]) << 8 |
            Int(readBuffer[3])
    }

    func readByte() -> Byte {

        var readBuffer : Byte = 0
        return self.read(&readBuffer, maxLength: sizeof(UInt8))
    }

I'd like to write a method to read Strings from the stream. Here is what I'm thinking:

• Read bytes (assume I know how many bytes to read)
• Conver the bytes to Character
• Append the Character into String

But the problem is how many bytes to read for a Character because the UTF8 length is variant? In general my question is how I'm supposed to read UTF8 String? Thanks in advance.

Just read to UnsafeMutablePointer buffer and convert it to a String. The returned String will be UTF8.

extension NSInputStream
{
    public func readString(length:Int) -> String {

        var str = ""

        if length > 0 {
            var readBuffer = UnsafeMutablePointer<UInt8>.alloc(length+1)

            var numberOfBytesRead = self.read(readBuffer, maxLength: length)
            if numberOfBytesRead == length {

                var buf = UnsafeMutablePointer<CChar>(readBuffer)
                buf[length] = 0
                // the C String must be null terminated
                if let utf8String = String.fromCString(buf) {
                    str = utf8String
                }
            }
            readBuffer.dealloc(length)
        }
        return str

    }
}