NSData.swift

// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2016 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//

import CoreFoundation

#if os(OSX) || os(iOS)
import Darwin
#elseif os(Linux)
import Glibc
#endif

extension NSData {
    public struct ReadingOptions : OptionSet {
        public let rawValue : UInt
        public init(rawValue: UInt) { self.rawValue = rawValue }
        
        public static let mappedIfSafe = ReadingOptions(rawValue: UInt(1 << 0))
        public static let uncached = ReadingOptions(rawValue: UInt(1 << 1))
        public static let alwaysMapped = ReadingOptions(rawValue: UInt(1 << 2))
    }

    public struct WritingOptions : OptionSet {
        public let rawValue : UInt
        public init(rawValue: UInt) { self.rawValue = rawValue }
        
        public static let atomic = WritingOptions(rawValue: UInt(1 << 0))
        public static let withoutOverwriting = WritingOptions(rawValue: UInt(1 << 1))
    }

    public struct SearchOptions : OptionSet {
        public let rawValue : UInt
        public init(rawValue: UInt) { self.rawValue = rawValue }
        
        public static let backwards = SearchOptions(rawValue: UInt(1 << 0))
        public static let anchored = SearchOptions(rawValue: UInt(1 << 1))
    }

    public struct Base64EncodingOptions : OptionSet {
        public let rawValue : UInt
        public init(rawValue: UInt) { self.rawValue = rawValue }
        
        public static let lineLength64Characters = Base64EncodingOptions(rawValue: UInt(1 << 0))
        public static let lineLength76Characters = Base64EncodingOptions(rawValue: UInt(1 << 1))
        public static let endLineWithCarriageReturn = Base64EncodingOptions(rawValue: UInt(1 << 4))
        public static let endLineWithLineFeed = Base64EncodingOptions(rawValue: UInt(1 << 5))
    }

    public struct Base64DecodingOptions : OptionSet {
        public let rawValue : UInt
        public init(rawValue: UInt) { self.rawValue = rawValue }
        
        public static let ignoreUnknownCharacters = Base64DecodingOptions(rawValue: UInt(1 << 0))
    }
}

private final class _NSDataDeallocator {
    var handler: (UnsafeMutableRawPointer, Int) -> Void = {_,_ in }
}

private let __kCFMutable: CFOptionFlags = 0x01
private let __kCFGrowable: CFOptionFlags = 0x02
private let __kCFMutableVarietyMask: CFOptionFlags = 0x03
private let __kCFBytesInline: CFOptionFlags = 0x04
private let __kCFUseAllocator: CFOptionFlags = 0x08
private let __kCFDontDeallocate: CFOptionFlags = 0x10
private let __kCFAllocatesCollectable: CFOptionFlags = 0x20

open class NSData : NSObject, NSCopying, NSMutableCopying, NSSecureCoding {
    typealias CFType = CFData
    
    private var _base = _CFInfo(typeID: CFDataGetTypeID())
    private var _length: CFIndex = 0
    private var _capacity: CFIndex = 0
    private var _deallocator: UnsafeMutableRawPointer? = nil // for CF only
    private var _deallocHandler: _NSDataDeallocator? = _NSDataDeallocator() // for Swift
    private var _bytes: UnsafeMutablePointer<UInt8>? = nil
    
    internal var _cfObject: CFType {
        if type(of: self) === NSData.self || type(of: self) === NSMutableData.self {
            return unsafeBitCast(self, to: CFType.self)
        } else {
            let bytePtr = self.bytes.bindMemory(to: UInt8.self, capacity: self.length)
            return CFDataCreate(kCFAllocatorSystemDefault, bytePtr, self.length)
        }
    }
    
    override open var _cfTypeID: CFTypeID {
        return CFDataGetTypeID()
    }

    // NOTE: the deallocator block here is implicitly @escaping by virtue of it being optional     
    public init(bytes: UnsafeMutableRawPointer?, length: Int, copy: Bool = false, deallocator: ((UnsafeMutableRawPointer, Int) -> Void)? = nil) {
        super.init()
        let options : CFOptionFlags = (type(of: self) == NSMutableData.self) ? __kCFMutable | __kCFGrowable : 0x0
        let bytePtr = bytes?.bindMemory(to: UInt8.self, capacity: length)
        if copy {
            _CFDataInit(unsafeBitCast(self, to: CFMutableData.self), options, length, bytePtr, length, false)
            if let handler = deallocator {
                handler(bytes!, length)
            }
        } else {
            if let handler = deallocator {
                _deallocHandler!.handler = handler
            }
            // The data initialization should flag that CF should not deallocate which leaves the handler a chance to deallocate instead
            _CFDataInit(unsafeBitCast(self, to: CFMutableData.self), options | __kCFDontDeallocate, length, bytePtr, length, true)
        }
    }
    
    public override convenience init() {
        let dummyPointer = unsafeBitCast(NSData.self, to: UnsafeMutableRawPointer.self)
        self.init(bytes: dummyPointer, length: 0, copy: false, deallocator: nil)
    }
    
    public convenience init(bytes: UnsafeRawPointer?, length: Int) {
        self.init(bytes: UnsafeMutableRawPointer(mutating: bytes), length: length, copy: true, deallocator: nil)
    }
    
    public convenience init(bytesNoCopy bytes: UnsafeMutableRawPointer, length: Int) {
        self.init(bytes: bytes, length: length, copy: false, deallocator: nil)
    }
    
    public convenience init(bytesNoCopy bytes: UnsafeMutableRawPointer, length: Int, freeWhenDone b: Bool) {
        self.init(bytes: bytes, length: length, copy: false) { buffer, length in
            if b {
                free(buffer)
            }
        }
    }

    // NOTE: the deallocator block here is implicitly @escaping by virtue of it being optional         
    public convenience init(bytesNoCopy bytes: UnsafeMutableRawPointer, length: Int, deallocator: ((UnsafeMutableRawPointer, Int) -> Void)? = nil) {
        self.init(bytes: bytes, length: length, copy: false, deallocator: deallocator)
    }
    public convenience init(contentsOfFile path: String, options readOptionsMask: ReadingOptions = []) throws {
        let readResult = try NSData.readBytesFromFileWithExtendedAttributes(path, options: readOptionsMask)
        self.init(bytes: readResult.bytes, length: readResult.length, copy: false, deallocator: readResult.deallocator)
    }
    
    public convenience init?(contentsOfFile path: String) {
        do {
            let readResult = try NSData.readBytesFromFileWithExtendedAttributes(path, options: [])
            self.init(bytes: readResult.bytes, length: readResult.length, copy: false, deallocator: readResult.deallocator)
        } catch {
            return nil
        }
    }
    
    public convenience init(data: Data) {
        self.init(bytes:data._nsObject.bytes, length: data.count)
    }
    
    public convenience init(contentsOf url: URL, options readOptionsMask: ReadingOptions = []) throws {
        if url.isFileURL {
            try self.init(contentsOfFile: url.path, options: readOptionsMask)
        } else {
            let session = URLSession(configuration: URLSessionConfiguration.defaultSessionConfiguration())
            let cond = NSCondition()
            var resError: NSError?
            var resData: Data?
            let task = session.dataTaskWithURL(url, completionHandler: { (data: Data?, response: URLResponse?, error: NSError?) -> Void in
                resData = data
                resError = error
                cond.broadcast()
            })
            task.resume()
            cond.wait()
            if resData == nil {
                throw resError!
            }
            self.init(data: resData!)
        }
    }
    
    public convenience init?(base64Encoded base64String: String, options: Base64DecodingOptions = []) {
        let encodedBytes = Array(base64String.utf8)
        guard let decodedBytes = NSData.base64DecodeBytes(encodedBytes, options: options) else {
            return nil
        }
        self.init(bytes: decodedBytes, length: decodedBytes.count)
    }
    
    
    /* Create an NSData from a Base-64, UTF-8 encoded NSData. By default, returns nil when the input is not recognized as valid Base-64.
     */
    public convenience init?(base64Encoded base64Data: Data, options: Base64DecodingOptions = []) {
        var encodedBytes = [UInt8](repeating: 0, count: base64Data.count)
        base64Data._nsObject.getBytes(&encodedBytes, length: encodedBytes.count)
        guard let decodedBytes = NSData.base64DecodeBytes(encodedBytes, options: options) else {
            return nil
        }
        self.init(bytes: decodedBytes, length: decodedBytes.count)
    }
    
    deinit {
        if let allocatedBytes = _bytes {
            _deallocHandler?.handler(allocatedBytes, _length)
        }
        if type(of: self) === NSData.self || type(of: self) === NSMutableData.self {
            _CFDeinit(self._cfObject)
        }
    }
    
    // MARK: - Funnel methods
    open var length: Int {
        return CFDataGetLength(_cfObject)
    }
    
    open var bytes: UnsafeRawPointer {
        return UnsafeRawPointer(CFDataGetBytePtr(_cfObject))
    }

    

    // MARK: - NSObject methods
    open override var hash: Int {
        return Int(bitPattern: CFHash(_cfObject))
    }
    
    open override func isEqual(_ object: AnyObject?) -> Bool {
        if let data = object as? NSData {
            return self.isEqual(to: data._swiftObject)
        } else {
            return false
        }
    }
    open func isEqual(to other: Data) -> Bool {
        if length != other.count {
            return false
        }
        
        return other.withUnsafeBytes { (bytes2: UnsafePointer<UInt8>) -> Bool in
            let bytes1 = bytes
            return memcmp(bytes1, bytes2, length) == 0
        }
    }
    
    open override func copy() -> Any {
        return copy(with: nil)
    }
    
    open func copy(with zone: NSZone? = nil) -> Any {
        return self
    }
    
    open override func mutableCopy() -> Any {
        return mutableCopy(with: nil)
    }
    
    open func mutableCopy(with zone: NSZone? = nil) -> Any {
        return NSMutableData(bytes: UnsafeMutableRawPointer(mutating: bytes), length: length, copy: true, deallocator: nil)
    }
    
    private func byteDescription(limit: Int? = nil) -> String {
        var s = ""
        var i = 0
        while i < self.length {
            if i > 0 && i % 4 == 0 {
                // if there's a limit, and we're at the barrier where we'd add the ellipses, don't add a space.
                if let limit = limit, self.length > limit && i == self.length - (limit / 2) { /* do nothing */ }
                else { s += " " }
            }
            let byte = bytes.load(fromByteOffset: i, as: UInt8.self)
            var byteStr = String(byte, radix: 16, uppercase: false)
            if byte <= 0xf { byteStr = "0\(byteStr)" }
            s += byteStr
            // if we've hit the midpoint of the limit, skip to the last (limit / 2) bytes.
            if let limit = limit, self.length > limit && i == (limit / 2) - 1 {
                s += " ... "
                i = self.length - (limit / 2)
            } else {
                i += 1
            }
        }
        return s
    }
    
    override open var debugDescription: String {
        return "<\(byteDescription(limit: 1024))>"
    }
    
    override open var description: String {
        return "<\(byteDescription())>"
    }
    
    
    // MARK: - NSCoding methods
    open func encode(with aCoder: NSCoder) {
        if let aKeyedCoder = aCoder as? NSKeyedArchiver {
            aKeyedCoder._encodePropertyList(self, forKey: "NS.data")
        } else {
            let bytePtr = self.bytes.bindMemory(to: UInt8.self, capacity: self.length)
            aCoder.encodeBytes(bytePtr, length: self.length)
        }
    }
    
    public required convenience init?(coder aDecoder: NSCoder) {
        if !aDecoder.allowsKeyedCoding {
            if let data = aDecoder.decodeData() {
                self.init(data: data)
            } else {
                return nil
            }
        } else if type(of: aDecoder) == NSKeyedUnarchiver.self || aDecoder.containsValue(forKey: "NS.data") {
            guard let data = aDecoder._decodePropertyListForKey("NS.data") as? NSData else {
                return nil
            }
            self.init(data: data._swiftObject)
        } else {
            let result : Data? = aDecoder.withDecodedUnsafeBufferPointer(forKey: "NS.bytes") {
                guard let buffer = $0 else { return nil }
                return Data(buffer: buffer)
            }
            
            guard let r = result else { return nil }
            self.init(data: r)
        }
    }
    
    public static var supportsSecureCoding: Bool {
        return true
    }

    // MARK: - IO
    internal struct NSDataReadResult {
        var bytes: UnsafeMutableRawPointer
        var length: Int
        var deallocator: ((_ buffer: UnsafeMutableRawPointer, _ length: Int) -> Void)?
    }
    
    internal static func readBytesFromFileWithExtendedAttributes(_ path: String, options: ReadingOptions) throws -> NSDataReadResult {
        let fd = _CFOpenFile(path, O_RDONLY)
        if fd < 0 {
            throw NSError(domain: NSPOSIXErrorDomain, code: Int(errno), userInfo: nil)
        }
        defer {
            close(fd)
        }

        var info = stat()
        let ret = withUnsafeMutablePointer(to: &info) { infoPointer -> Bool in
            if fstat(fd, infoPointer) < 0 {
                return false
            }
            return true
        }
        
        if !ret {
            throw NSError(domain: NSPOSIXErrorDomain, code: Int(errno), userInfo: nil)
        }
        
        let length = Int(info.st_size)
        
        if options.contains(.alwaysMapped) {
            let data = mmap(nil, length, PROT_READ, MAP_PRIVATE, fd, 0)
            
            // Swift does not currently expose MAP_FAILURE
            if data != UnsafeMutableRawPointer(bitPattern: -1) {
                return NSDataReadResult(bytes: data!, length: length) { buffer, length in
                    munmap(buffer, length)
                }
            }
            
        }
        
        let data = malloc(length)!
        var remaining = Int(info.st_size)
        var total = 0
        while remaining > 0 {
            let amt = read(fd, data.advanced(by: total), remaining)
            if amt < 0 {
                break
            }
            remaining -= amt
            total += amt
        }

        if remaining != 0 {
            throw NSError(domain: NSPOSIXErrorDomain, code: Int(errno), userInfo: nil)
        }
        
        return NSDataReadResult(bytes: data, length: length) { buffer, length in
            free(buffer)
        }
    }
    
    internal func makeTemporaryFile(inDirectory dirPath: String) throws -> (Int32, String) {
        let template = dirPath._nsObject.appendingPathComponent("tmp.XXXXXX")
        let maxLength = Int(PATH_MAX) + 1
        var buf = [Int8](repeating: 0, count: maxLength)
        let _ = template._nsObject.getFileSystemRepresentation(&buf, maxLength: maxLength)
        let fd = mkstemp(&buf)
        if fd == -1 {
            throw _NSErrorWithErrno(errno, reading: false, path: dirPath)
        }
        let pathResult = FileManager.default.string(withFileSystemRepresentation:buf, length: Int(strlen(buf)))
        return (fd, pathResult)
    }

    internal class func write(toFileDescriptor fd: Int32, path: String? = nil, buf: UnsafeRawPointer, length: Int) throws {
        var bytesRemaining = length
        while bytesRemaining > 0 {
            var bytesWritten : Int
            repeat {
                #if os(OSX) || os(iOS)
                    bytesWritten = Darwin.write(fd, buf.advanced(by: length - bytesRemaining), bytesRemaining)
                #elseif os(Linux)
                    bytesWritten = Glibc.write(fd, buf.advanced(by: length - bytesRemaining), bytesRemaining)
                #endif
            } while (bytesWritten < 0 && errno == EINTR)
            if bytesWritten <= 0 {
                throw _NSErrorWithErrno(errno, reading: false, path: path)
            } else {
                bytesRemaining -= bytesWritten
            }
        }
    }
    
    open func write(toFile path: String, options writeOptionsMask: WritingOptions = []) throws {
        var fd : Int32
        var mode : mode_t? = nil
        let useAuxiliaryFile = writeOptionsMask.contains(.atomic)
        var auxFilePath : String? = nil
        if useAuxiliaryFile {
            // Preserve permissions.
            var info = stat()
            if lstat(path, &info) == 0 {
                mode = info.st_mode
            } else if errno != ENOENT && errno != ENAMETOOLONG {
                throw _NSErrorWithErrno(errno, reading: false, path: path)
            }
            let (newFD, path) = try self.makeTemporaryFile(inDirectory: path._nsObject.deletingLastPathComponent)
            fd = newFD
            auxFilePath = path
            fchmod(fd, 0o666)
        } else {
            var flags = O_WRONLY | O_CREAT | O_TRUNC
            if writeOptionsMask.contains(.withoutOverwriting) {
                flags |= O_EXCL
            }
            fd = _CFOpenFileWithMode(path, flags, 0o666)
        }
        if fd == -1 {
            throw _NSErrorWithErrno(errno, reading: false, path: path)
        }
        defer {
            close(fd)
        }

        try self.enumerateByteRangesUsingBlockRethrows { (buf, range, stop) in
            if range.length > 0 {
                do {
                    try NSData.write(toFileDescriptor: fd, path: path, buf: buf, length: range.length)
                    if fsync(fd) < 0 {
                        throw _NSErrorWithErrno(errno, reading: false, path: path)
                    }
                } catch let err {
                    if let auxFilePath = auxFilePath {
                        do {
                            try FileManager.default.removeItem(atPath: auxFilePath)
                        } catch _ {}
                    }
                    throw err
                }
            }
        }
        if let auxFilePath = auxFilePath {
            if rename(auxFilePath, path) != 0 {
                do {
                    try FileManager.default.removeItem(atPath: auxFilePath)
                } catch _ {}
                throw _NSErrorWithErrno(errno, reading: false, path: path)
            }
            if let mode = mode {
                chmod(path, mode)
            }
        }
    }
    
    /// NOTE: the 'atomically' flag is ignored if the url is not of a type the supports atomic writes
    open func write(toFile path: String, atomically useAuxiliaryFile: Bool) -> Bool {
        do {
            try write(toFile: path, options: useAuxiliaryFile ? .atomic : [])
        } catch {
            return false
        }
        return true
    }
    
    /// NOTE: the 'atomically' flag is ignored if the url is not of a type the supports atomic writes
    open func write(to url: URL, atomically: Bool) -> Bool {
        if url.isFileURL {
            return write(toFile: url.path, atomically: atomically)
        }
        return false
    }

    ///    Write the contents of the receiver to a location specified by the given file URL.
    ///
    ///    - parameter url:              The location to which the receiver’s contents will be written.
    ///    - parameter writeOptionsMask: An option set specifying file writing options.
    ///
    ///    - throws: This method returns Void and is marked with the `throws` keyword to indicate that it throws an error in the event of failure.
    ///
    ///      This method is invoked in a `try` expression and the caller is responsible for handling any errors in the `catch` clauses of a `do` statement, as described in [Error Handling](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/ErrorHandling.html#//apple_ref/doc/uid/TP40014097-CH42) in [The Swift Programming Language](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/Swift_Programming_Language/index.html#//apple_ref/doc/uid/TP40014097) and [Error Handling](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/AdoptingCocoaDesignPatterns.html#//apple_ref/doc/uid/TP40014216-CH7-ID10) in [Using Swift with Cocoa and Objective-C](https://developer.apple.com/library/prerelease/ios/documentation/Swift/Conceptual/BuildingCocoaApps/index.html#//apple_ref/doc/uid/TP40014216).
    open func write(to url: URL, options writeOptionsMask: WritingOptions = []) throws {
        guard url.isFileURL else {
            let userInfo = [NSLocalizedDescriptionKey : "The folder at “\(url)” does not exist or is not a file URL.", // NSLocalizedString() not yet available
                            NSURLErrorKey             : url.absoluteString] as Dictionary<String, Any>
            throw NSError(domain: NSCocoaErrorDomain, code: 4, userInfo: userInfo)
        }
        try write(toFile: url.path, options: writeOptionsMask)
    }
    
    
    // MARK: - Bytes
    open func getBytes(_ buffer: UnsafeMutableRawPointer, length: Int) {
        let bytePtr = buffer.bindMemory(to: UInt8.self, capacity: length)
        CFDataGetBytes(_cfObject, CFRangeMake(0, length), bytePtr)
    }
    
    open func getBytes(_ buffer: UnsafeMutableRawPointer, range: NSRange) {
        let bytePtr = buffer.bindMemory(to: UInt8.self, capacity: range.length)
        CFDataGetBytes(_cfObject, CFRangeMake(range.location, range.length), bytePtr)
    }
    
    open func subdata(with range: NSRange) -> Data {
        if range.length == 0 {
            return Data()
        }
        if range.location == 0 && range.length == self.length {
            return Data(referencing: self)
        }
        let p = self.bytes.advanced(by: range.location).bindMemory(to: UInt8.self, capacity: range.length)
        return Data(bytes: p, count: range.length)
    }
    
    open func range(of dataToFind: Data, options mask: SearchOptions = [], in searchRange: NSRange) -> NSRange {
        let dataToFind = dataToFind._nsObject
        guard dataToFind.length > 0 else {return NSRange(location: NSNotFound, length: 0)}
        guard let searchRange = searchRange.toRange() else {fatalError("invalid range")}
        
        precondition(searchRange.upperBound <= self.length, "range outside the bounds of data")

        let basePtr = self.bytes.bindMemory(to: UInt8.self, capacity: self.length)
        let baseData = UnsafeBufferPointer<UInt8>(start: basePtr, count: self.length)[searchRange]
        let searchPtr = dataToFind.bytes.bindMemory(to: UInt8.self, capacity: dataToFind.length)
        let search = UnsafeBufferPointer<UInt8>(start: searchPtr, count: dataToFind.length)
        
        let location : Int?
        let anchored = mask.contains(.anchored)
        if mask.contains(.backwards) {
            location = NSData.searchSubSequence(search.reversed(), inSequence: baseData.reversed(),anchored : anchored).map {$0.base-search.count}
        } else {
            location = NSData.searchSubSequence(search, inSequence: baseData,anchored : anchored)
        }
        return location.map {NSRange(location: $0, length: search.count)} ?? NSRange(location: NSNotFound, length: 0)
    }
    private static func searchSubSequence<T : Collection, T2 : Sequence>(_ subSequence : T2, inSequence seq: T,anchored : Bool) -> T.Index? where T.Iterator.Element : Equatable, T.Iterator.Element == T2.Iterator.Element, T.SubSequence.Iterator.Element == T.Iterator.Element, T.Indices.Iterator.Element == T.Index {
        for index in seq.indices {
            if seq.suffix(from: index).starts(with: subSequence) {
                return index
            }
            if anchored {return nil}
        }
        return nil
    }
    
    internal func enumerateByteRangesUsingBlockRethrows(_ block: (UnsafeRawPointer, NSRange, UnsafeMutablePointer<Bool>) throws -> Void) throws {
        var err : Swift.Error? = nil
        self.enumerateBytes() { (buf, range, stop) -> Void in
            do {
                try block(buf, range, stop)
            } catch let e {
                err = e
            }
        }
        if let err = err {
            throw err
        }
    }

    /// 'block' is called once for each contiguous region of memory in the receiver (once total for contiguous NSDatas), until either all bytes have been enumerated, or the 'stop' parameter is set to true.
    open func enumerateBytes(_ block: (UnsafeRawPointer, NSRange, UnsafeMutablePointer<Bool>) -> Void) {
        var stop = false
        withUnsafeMutablePointer(to: &stop) { stopPointer in
            if (stopPointer.pointee) {
                return
            }
            block(bytes, NSMakeRange(0, length), stopPointer)
        }
    }
    
    // MARK: - Base64 Methods

    /// Create a Base-64 encoded String from the receiver's contents using the given options.
    open func base64EncodedString(options: Base64EncodingOptions = []) -> String {
        var decodedBytes = [UInt8](repeating: 0, count: self.length)
        getBytes(&decodedBytes, length: decodedBytes.count)
        let encodedBytes = NSData.base64EncodeBytes(decodedBytes, options: options)
        let characters = encodedBytes.map { Character(UnicodeScalar($0)) }
        return String(characters)
    }

    /// Create a Base-64, UTF-8 encoded Data from the receiver's contents using the given options.
    open func base64EncodedData(options: Base64EncodingOptions = []) -> Data {
        var decodedBytes = [UInt8](repeating: 0, count: self.length)
        getBytes(&decodedBytes, length: decodedBytes.count)
        let encodedBytes = NSData.base64EncodeBytes(decodedBytes, options: options)
        return Data(bytes: encodedBytes, count: encodedBytes.count)
    }

    /// The ranges of ASCII characters that are used to encode data in Base64.
    private static let base64ByteMappings: [Range<UInt8>] = [
        65 ..< 91,      // A-Z
        97 ..< 123,     // a-z
        48 ..< 58,      // 0-9
        43 ..< 44,      // +
        47 ..< 48,      // /
    ]
    /**
     Padding character used when the number of bytes to encode is not divisible by 3
     */
    private static let base64Padding : UInt8 = 61 // =
    
    /**
     This method takes a byte with a character from Base64-encoded string
     and gets the binary value that the character corresponds to.
     
     - parameter byte:       The byte with the Base64 character.
     - returns:              Base64DecodedByte value containing the result (Valid , Invalid, Padding)
     */
    private enum Base64DecodedByte {
        case valid(UInt8)
        case invalid
        case padding
    }
    private static func base64DecodeByte(_ byte: UInt8) -> Base64DecodedByte {
        guard byte != base64Padding else {return .padding}
        var decodedStart: UInt8 = 0
        for range in base64ByteMappings {
            if range.contains(byte) {
                let result = decodedStart + (byte - range.lowerBound)
                return .valid(result)
            }
            decodedStart += range.upperBound - range.lowerBound
        }
        return .invalid
    }
    
    /**
     This method takes six bits of binary data and encodes it as a character
     in Base64.
     
     The value in the byte must be less than 64, because a Base64 character
     can only represent 6 bits.
     
     - parameter byte:       The byte to encode
     - returns:              The ASCII value for the encoded character.
     */
    private static func base64EncodeByte(_ byte: UInt8) -> UInt8 {
        assert(byte < 64)
        var decodedStart: UInt8 = 0
        for range in base64ByteMappings {
            let decodedRange = decodedStart ..< decodedStart + (range.upperBound - range.lowerBound)
            if decodedRange.contains(byte) {
                return range.lowerBound + (byte - decodedStart)
            }
            decodedStart += range.upperBound - range.lowerBound
        }
        return 0
    }
    
    
    /**
     This method decodes Base64-encoded data.
     
     If the input contains any bytes that are not valid Base64 characters,
     this will return nil.
     
     - parameter bytes:      The Base64 bytes
     - parameter options:    Options for handling invalid input
     - returns:              The decoded bytes.
     */
    private static func base64DecodeBytes(_ bytes: [UInt8], options: Base64DecodingOptions = []) -> [UInt8]? {
        var decodedBytes = [UInt8]()
        decodedBytes.reserveCapacity((bytes.count/3)*2)
        
        var currentByte : UInt8 = 0
        var validCharacterCount = 0
        var paddingCount = 0
        var index = 0
        
        
        for base64Char in bytes {
            
            let value : UInt8
            
            switch base64DecodeByte(base64Char) {
            case .valid(let v):
                value = v
                validCharacterCount += 1
            case .invalid:
                if options.contains(.ignoreUnknownCharacters) {
                    continue
                } else {
                    return nil
                }
            case .padding:
                paddingCount += 1
                continue
            }
            
            //padding found in the middle of the sequence is invalid
            if paddingCount > 0 {
                return nil
            }
            
            switch index%4 {
            case 0:
                currentByte = (value << 2)
            case 1:
                currentByte |= (value >> 4)
                decodedBytes.append(currentByte)
                currentByte = (value << 4)
            case 2:
                currentByte |= (value >> 2)
                decodedBytes.append(currentByte)
                currentByte = (value << 6)
            case 3:
                currentByte |= value
                decodedBytes.append(currentByte)
            default:
                fatalError()
            }
            
            index += 1
        }
        
        guard (validCharacterCount + paddingCount)%4 == 0 else {
            //invalid character count
            return nil
        }
        return decodedBytes
    }
    
    
    /**
     This method encodes data in Base64.
     
     - parameter bytes:      The bytes you want to encode
     - parameter options:    Options for formatting the result
     - returns:              The Base64-encoding for those bytes.
     */
    private static func base64EncodeBytes(_ bytes: [UInt8], options: Base64EncodingOptions = []) -> [UInt8] {
        var result = [UInt8]()
        result.reserveCapacity((bytes.count/3)*4)
        
        let lineOptions : (lineLength : Int, separator : [UInt8])? = {
            let lineLength: Int
            
            if options.contains(.lineLength64Characters) { lineLength = 64 }
            else if options.contains(.lineLength76Characters) { lineLength = 76 }
            else {
                return nil
            }
            
            var separator = [UInt8]()
            if options.contains(.endLineWithCarriageReturn) { separator.append(13) }
            if options.contains(.endLineWithLineFeed) { separator.append(10) }
            
            //if the kind of line ending to insert is not specified, the default line ending is Carriage Return + Line Feed.
            if separator.count == 0 {separator = [13,10]}
            
            return (lineLength,separator)
        }()
        
        var currentLineCount = 0
        let appendByteToResult : (UInt8) -> () = {
            result.append($0)
            currentLineCount += 1
            if let options = lineOptions, currentLineCount == options.lineLength {
                result.append(contentsOf: options.separator)
                currentLineCount = 0
            }
        }
        
        var currentByte : UInt8 = 0
        
        for (index,value) in bytes.enumerated() {
            switch index%3 {
            case 0:
                currentByte = (value >> 2)
                appendByteToResult(NSData.base64EncodeByte(currentByte))
                currentByte = ((value << 6) >> 2)
            case 1:
                currentByte |= (value >> 4)
                appendByteToResult(NSData.base64EncodeByte(currentByte))
                currentByte = ((value << 4) >> 2)
            case 2:
                currentByte |= (value >> 6)
                appendByteToResult(NSData.base64EncodeByte(currentByte))
                currentByte = ((value << 2) >> 2)
                appendByteToResult(NSData.base64EncodeByte(currentByte))
            default:
                fatalError()
            }
        }
        //add padding
        switch bytes.count%3 {
        case 0: break //no padding needed
        case 1:
            appendByteToResult(NSData.base64EncodeByte(currentByte))
            appendByteToResult(self.base64Padding)
            appendByteToResult(self.base64Padding)
        case 2:
            appendByteToResult(NSData.base64EncodeByte(currentByte))
            appendByteToResult(self.base64Padding)
        default:
            fatalError()
        }
        return result
    }
    
}

// MARK: -
extension NSData : _CFBridgable, _SwiftBridgable {
    typealias SwiftType = Data
    internal var _swiftObject: SwiftType { return Data(referencing: self) }
    
    public func bridge() -> Data {
        return _swiftObject
    }
}

extension Data : _NSBridgable, _CFBridgable {
    typealias CFType = CFData
    typealias NSType = NSData
    internal var _cfObject: CFType { return _nsObject._cfObject }
    internal var _nsObject: NSType { return _bridgeToObjectiveC() }
    
    public func bridge() -> NSData {
        return _nsObject
    }
}

extension CFData : _NSBridgable, _SwiftBridgable {
    typealias NSType = NSData
    typealias SwiftType = Data
    internal var _nsObject: NSType { return unsafeBitCast(self, to: NSType.self) }
    internal var _swiftObject: SwiftType { return Data(referencing: self._nsObject) }
}

// MARK: -
open class NSMutableData : NSData {
    internal var _cfMutableObject: CFMutableData { return unsafeBitCast(self, to: CFMutableData.self) }
    
    // NOTE: the deallocator block here is implicitly @escaping by virtue of it being optional
    public override init(bytes: UnsafeMutableRawPointer?, length: Int, copy: Bool = false, deallocator: (/*@escaping*/ (UnsafeMutableRawPointer, Int) -> Void)? = nil) {
        super.init(bytes: bytes, length: length, copy: copy, deallocator: deallocator)
    }
    public init() {
        self.init(bytes: nil, length: 0)
    }
        
    public convenience init?(capacity: Int) {
        self.init(bytes: nil, length: 0)
    }
    
    public convenience init?(length: Int) {
        self.init(bytes: nil, length: 0)
        self.length = length
    }
    
    // MARK: - Funnel Methods
    open var mutableBytes: UnsafeMutableRawPointer {
        return UnsafeMutableRawPointer(CFDataGetMutableBytePtr(_cfMutableObject))
    }
    
    open override var length: Int {
        get {
            return CFDataGetLength(_cfObject)
        }
        set {
            CFDataSetLength(_cfMutableObject, newValue)
        }
    }
    
    // MARK: - NSObject
    open override func copy(with zone: NSZone? = nil) -> Any {
        return NSData(bytes: bytes, length: length)
    }

    // MARK: - Mutability
    open func append(_ bytes: UnsafeRawPointer, length: Int) {
        let bytePtr = bytes.bindMemory(to: UInt8.self, capacity: length)
        CFDataAppendBytes(_cfMutableObject, bytePtr, length)
    }
    
    open func append(_ other: Data) {
        let otherLength = other.count
        other.withUnsafeBytes {
            append($0, length: otherLength)
        }
        
    }
    
    open func increaseLength(by extraLength: Int) {
        CFDataSetLength(_cfMutableObject, CFDataGetLength(_cfObject) + extraLength)
    }
    
    open func replaceBytes(in range: NSRange, withBytes bytes: UnsafeRawPointer) {
        let bytePtr = bytes.bindMemory(to: UInt8.self, capacity: length)
        CFDataReplaceBytes(_cfMutableObject, CFRangeMake(range.location, range.length), bytePtr, length)
    }
    
    open func resetBytes(in range: NSRange) {
        bzero(mutableBytes.advanced(by: range.location), range.length)
    }
    
    open func setData(_ data: Data) {
        length = data.count
        data.withUnsafeBytes {
            replaceBytes(in: NSMakeRange(0, length), withBytes: $0)
        }
        
    }
    
    open func replaceBytes(in range: NSRange, withBytes replacementBytes: UnsafeRawPointer?, length replacementLength: Int) {
        if let replacementBytes = replacementBytes {
            let bytePtr = replacementBytes.bindMemory(to: UInt8.self, capacity: replacementLength)
            CFDataReplaceBytes(_cfMutableObject, CFRangeMake(range.location, range.length), bytePtr, replacementLength)
        }
    }
}

extension NSData : _StructTypeBridgeable {
    public typealias _StructType = Data
    public func _bridgeToSwift() -> Data {
        return Data._unconditionallyBridgeFromObjectiveC(self)
    }
}