Size of the NSInputStream buffer - ios

Question

I'm trying to use NSInputStream for receiving data using TCP socket connection. On the server side I send data size before sending of the data itself. on the iOS client side I need to extract first 4 bytes from the NSInputStream, because I need to check if size of data has received completely, but I have a problem with it:
...
case NSStreamEvent.HasBytesAvailable:
if ( aStream == inputstream){
while (inputstream.hasBytesAvailable){
var readBufferRef = UnsafeMutablePointer<UnsafeMutablePointer<UInt8>>()
var readBufferLengthRef = 0
let readBufferIsAvailable = inputstream.getBuffer(readBufferRef, length: &readBufferLengthRef)
...
}
}
break
After receiving of data readBufferLengthRef always equals to 0.
How it can be?
And how can I get size of the NSInputStream buffer?
UPD:
Code:
case NSStreamEvent.HasBytesAvailable:
NSLog("HasBytesAvaible")
var buffer = [UInt8](count: 1024, repeatedValue: 0)
if ( aStream == inputstream){
while (inputstream.hasBytesAvailable){
var readBufferRef: UnsafeMutablePointer<UInt8> = nil
var readBufferLengthRef = 0
let readBufferIsAvailable = inputstream.getBuffer(&readBufferRef, length: &readBufferLengthRef)
//debugger: readBufferLengthRef = (int)0
}
}
break

Answer 1

In your code, readBufferRef is defined as a "pointer to a pointer"
but never allocated, and therefore it is the NULL pointer.
What you should do is to pass the address of an
UnsafeMutablePointer<UInt8> as an inout argument to the function
(assuming Swift 2):
var readBufferRef: UnsafeMutablePointer<UInt8> = nil
var readBufferLengthRef = 0
let readBufferIsAvailable = inputStream.getBuffer(&readBufferRef, length: &readBufferLengthRef)
On return, readBufferRef is set to the read buffer of the stream (valid until the next read operation), and readBufferLengthRef contains
the number of available bytes.