How to test if my remote socket NSStream are correctly open

Question

TL;DR : What's the way to check if my remote stream are opened correctly after a call to NSStream.getStreamsToHostWithName(...)?

My application is a mobile IOS8 swift application.

I am using NSStream for input and output socket communication with a remote server.

To connect to my server and open my stream I use this code:

func connect(host: String, port: Int) -> Bool
{
    //clear the previous connection if existing (and update self.connected)
    disconnect()
    //updating the current connection
    self.host = host
    self.port = port

    //pairing NSstreams with remote connection
    NSStream.getStreamsToHostWithName(self.host!, port: self.port!, inputStream: &inputStream, outputStream: &outputStream)

    if (self.inputStream != nil && self.outputStream != nil)
    {
        //open streams
        self.inputStream?.open()
        self.outputStream?.open()
    }
    if self.outputStream?.streamError == nil && self.inputStream?.streamError == nil
    {
        println("SOK")    //PROBLEM 1
    }
    //error checking after opening streams // PROBLEM 2
    if var inputStreamErr: CFError = CFReadStreamCopyError(self.inputStream)?
    {
        println("InputStream error : " + CFErrorCopyDescription(inputStreamErr))
    }
    else if var outputStreamErr: CFError = CFWriteStreamCopyError(self.outputStream)?
    {
        println("OutStream error : " + CFErrorCopyDescription(outputStreamErr))
    }
    else
    {
        //set the delegate to self
        self.inputStream?.delegate = self
        self.outputStream?.delegate = self
        self.connected = true
    }
    //return connection state
    return self.connected
}

My problem is located at //PROBLEM1 and //PROBLEM2.

At these points I try to determine if my sockets are opened correctly, but even if the server is not running this code still works, then the read and write operations are failing. I would like to be able to determine if the connection failed or not.

Maybe I am doing it totally wrong, I don't get how to test this.

score 30 · Accepted Answer · edited Oct 17 '16 at 10:18

First of all, you have to schedule the stream on a runloop:

inputStream!.scheduleInRunLoop(.mainRunLoop(), forMode: NSDefaultRunLoopMode)
outputStream!.scheduleInRunLoop(.mainRunLoop(), forMode: NSDefaultRunLoopMode)

And, in your code, it's too soon to check the error. Because open() is async operation, you have to wait the result using delegate. Here is working example:

import Foundation

class Connection: NSObject, NSStreamDelegate {
var host:String?
var port:Int?
var inputStream: NSInputStream?
var outputStream: NSOutputStream?

func connect(host: String, port: Int) {

    self.host = host
    self.port = port

    NSStream.getStreamsToHostWithName(host, port: port, inputStream: &inputStream, outputStream: &outputStream)

    if inputStream != nil && outputStream != nil {

        // Set delegate
        inputStream!.delegate = self
        outputStream!.delegate = self

        // Schedule
        inputStream!.scheduleInRunLoop(.mainRunLoop(), forMode: NSDefaultRunLoopMode)
        outputStream!.scheduleInRunLoop(.mainRunLoop(), forMode: NSDefaultRunLoopMode)

        print("Start open()")

        // Open!
        inputStream!.open()
        outputStream!.open()
    }
}

func stream(aStream: NSStream, handleEvent eventCode: NSStreamEvent) {
    if aStream === inputStream {
        switch eventCode {
        case NSStreamEvent.ErrorOccurred:
            print("input: ErrorOccurred: \(aStream.streamError?.description)")
        case NSStreamEvent.OpenCompleted:
            print("input: OpenCompleted")
        case NSStreamEvent.HasBytesAvailable:
            print("input: HasBytesAvailable")

            // Here you can `read()` from `inputStream`

        default:
            break
        }
    }
    else if aStream === outputStream {
        switch eventCode {
        case NSStreamEvent.ErrorOccurred:
            print("output: ErrorOccurred: \(aStream.streamError?.description)")
        case NSStreamEvent.OpenCompleted:
            print("output: OpenCompleted")
        case NSStreamEvent.HasSpaceAvailable:
            print("output: HasSpaceAvailable")

            // Here you can write() to `outputStream`

        default:
            break
        }
    }
}

}

Then:

let conn = Connection()
conn.connect("www.example.com", port: 80)

Thanks for this precise answer. I just have some questions. First, does doing the schedule part make my streams async? I want my operations to be synchronous. — , Feb 26 '15 at 05:59
With my understanding, stream itself is always non-blocking. If you need synchronous operation, you have to use polling with `while true { ... }` loop. see: https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/Streams/Articles/PollingVersusRunloop.html — rintaro, Feb 26 '15 at 07:53
I think stream is blocking, the NSInputStream.read() operation is blocking by default — , Feb 26 '15 at 08:11
Anyway, I used your answer to reshape my whole class. I am starting swift and it made me grasp delegates, events handling and runloop in swift. Thanks a lot! — , Feb 26 '15 at 08:14
Where i have to write this two lines ? inputStream!.scheduleInRunLoop(.mainRunLoop(), forMode: NSDefaultRunLoopMode) outputStream!.scheduleInRunLoop(.mainRunLoop(), forMode: NSDefaultRunLoopMode) — , Mar 03 '15 at 14:48
I am having same problem here : https://stackoverflow.com/questions/51938300/how-to-know-if-remote-stream-socket-throw-an-errror-while-try-to-get-connect . I added handle Event method after this but it's not triggering Any help Please.. — tp2376, Aug 21 '18 at 12:48

How to test if my remote socket NSStream are correctly open

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