Swift Toys

BinaryDataScanner.swift

//
//  BinaryDataScanner.swift
//
//  Created by Dave Peck on 7/20/14.
//  Copyright (c) 2014 Dave Peck. All rights reserved.
// 
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

import Foundation

/* 
    Toying with tools to help read binary formats.

    I've seen lots of approaches in swift that create
    an intermediate object per-read (usually another NSData)
    but even if these are lightweight under the hood,
    it seems like overkill. Plus this taught me about <()> aka <Void>
 
    And it would be nice to have an extension to
    NSFileHandle too that does much the same.
*/

protocol BinaryReadable {
    var littleEndian: Self { get }
    var bigEndian: Self { get }
}

extension UInt8: BinaryReadable {
    var littleEndian: UInt8 { return self }
    var bigEndian: UInt8 { return self }
}

extension UInt16: BinaryReadable {}

extension UInt32: BinaryReadable {}

extension UInt64: BinaryReadable {}

class BinaryDataScanner {
    let data: NSData
    let littleEndian: Bool
    let encoding: NSStringEncoding

    var current: UnsafePointer<Void>
    var remaining: Int
    
    init(data: NSData, littleEndian: Bool, encoding: NSStringEncoding) {
        self.data = data
        self.littleEndian = littleEndian
        self.encoding = encoding

        self.current = self.data.bytes
        self.remaining = self.data.length
    }
    
    func read<T: BinaryReadable>() -> T? {
        if remaining < sizeof(T) {
            return nil
        }
        
        let tCurrent = UnsafePointer<T>(current)
        let v = tCurrent.memory
        current = UnsafePointer<Void>(tCurrent.successor())
        remaining -= sizeof(T)
        return littleEndian ? v.littleEndian : v.bigEndian
    }
    
    /* convenience read funcs */
    
    func readByte() -> UInt8? {
        return read()
    }
    
    func read16() -> UInt16? {
        return read()
    }
    
    func read32() -> UInt32? {
        return read()
    }
    
    func read64() -> UInt64? {
        return read()
    }
    
    func readNullTerminatedString() -> String? {
        var string:String? = nil
        var tCurrent = UnsafePointer<UInt8>(current)
        var count: Int = 0
        
        // scan
        while (remaining > 0 && tCurrent.memory != 0) {
            remaining -= 1
            count += 1
            tCurrent = tCurrent.successor()
        }
        
        // create string if available
        if (remaining > 0 && tCurrent.memory == 0) {
            string = NSString(bytes: current, length: count, encoding: encoding) as String
            current = UnsafePointer<()>(tCurrent.successor())
            remaining -= 1
        }
        
        return string
    }
}

Would be really nice to have a func readEndian<T>(byteCount: Int) -> T? that calls underlying read<T>() and then uses the scanner's littleEndian property to return the correct final value... doesn't seem possible since there's no common protocol?

Thanks to @natecook1000 -- have an answer for that.

Updated for swiftb6

Is there anything special I need todo in order to read a float? I tried to do it the way you did Int but i'm not getting the correct value.

@arunvenkate Just noticed your question. I haven't actually updated this for Swift 1.0 (or 1.1 betas) but in theory I think it should work?