Keychain.swift

import Foundation
import Security

private let keychainQueue = dispatch_queue_create("networking.keychain", DISPATCH_QUEUE_CONCURRENT)

public class Keychain {
    private let service: String
    public init(service: String) {
        self.service = service
    }

    public subscript(key: String) -> String? {
        get {
            return getItem(key)
        }
        set(newValue) {
            setItem(newValue, forKey: key)
        }
    }

    public func deleteAll() {
        let query: [String : AnyObject] = [
            kSecClass       : kSecClassGenericPassword,
            kSecAttrService : service,
        ]
        dispatch_barrier_async(keychainQueue, {
            SecItemDelete(query)
            return
        })
    }

    private func setItem(value: String?, forKey key: String) {
        deleteItem(key)
        if let value = value {
            addItem(value, forKey: key)
        }
    }
    
    private func addItem(value: String, forKey key: String) {
        let data = value.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)
        if let data = data {
            let query: [String : AnyObject] = [
                kSecClass       : kSecClassGenericPassword,
                kSecAttrService : service,
                kSecAttrAccount : key,
                kSecValueData   : data,
            ]
            dispatch_barrier_async(keychainQueue, {
                SecItemAdd(query, nil)
                return
            })
        }
    }

    private func deleteItem(key: String) {
        let query: [String : AnyObject] = [
            kSecClass       : kSecClassGenericPassword,
            kSecAttrService : service,
            kSecAttrAccount : key,
        ]
        dispatch_barrier_async(keychainQueue, {
            SecItemDelete(query)
            return
        })
    }
    
    private func getItem(key: String) -> String? {
        let query: [String : AnyObject] = [
            kSecClass       : kSecClassGenericPassword,
            kSecAttrService : service,
            kSecAttrAccount : key,
            kSecReturnData  : kCFBooleanTrue,
            kSecMatchLimit  : kSecMatchLimitOne,
        ]

        var value: String?
        dispatch_sync(keychainQueue, {
            var dataDescriptorRef: Unmanaged<AnyObject>?
            SecItemCopyMatching(query, &dataDescriptorRef)
            let dataDescriptor = dataDescriptorRef?.toOpaque()

            if let dataDescriptor = dataDescriptor {
                let data = Unmanaged<NSData>.fromOpaque(dataDescriptor).takeUnretainedValue()
                value = NSString(data: data, encoding: NSUTF8StringEncoding)
            }
        })
        return value
    }
}

KeychainTests.swift

import Foundation
import XCTest
import Networking

class KeychainTests: XCTestCase {
    let keychain: Keychain = Keychain(service: "service")

    override func tearDown() {
        keychain.deleteAll()
    }

    func testEmpty() {
        XCTAssertNil(keychain["key1"], "Value should be nil")
    }
    
    func testAdd() {
        keychain["key1"] = "value1"
        let value = keychain["key1"]
        XCTAssertNotNil(value, "Value should not be nil")
        if let value = value {
            XCTAssertEqual(value, "value1", "Value should be properly set")
        }
    }
    
    func testSet() {
        keychain["key1"] = "value1"
        keychain["key1"] = "value2"
        let value = keychain["key1"]
        XCTAssertNotNil(value, "Value should not be nil")
        if let value = value {
            XCTAssertEqual(value, "value2", "Value should be properly set")
        }
    }
    
    func testDelete() {
        keychain["key1"] = "value1"
        keychain["key1"] = nil
        XCTAssertNil(keychain["key1"], "Value should be nil")
    }
    
    func testDeleteAll() {
        keychain["key1"] = "value1"
        keychain["key2"] = "value2"
        keychain.deleteAll()
        XCTAssertNil(keychain["key1"], "Value should be nil")
        XCTAssertNil(keychain["key2"], "Value should be nil")
    }
    
    func testTwoKeychains() {
        let keychain2: Keychain = Keychain(service: "service")
        keychain2["key1"] = "value1"

        let value = keychain["key1"]
        XCTAssertNotNil(value, "Value should not be nil")
        if let value = value {
            XCTAssertEqual(value, "value1", "Value should be properly set")
        }
    }
}