Currently tail recursion is not guaranteed in Swift

[jazzbox]

This is especially problematic in Debug mode, where no tail recursion exists! I found this when some JPEGs crashed my App. This could also easily be used as an attack vector with specially crafted data.

My Solution for parsing JPEGs is to translate the parse function into a looped version:

private typealias JPEGParseTuple = (data: NSData, offset: Int, segment: JPEGHeaderSegment)

private enum JPEGParseResult {
    case Size(CGSize)
    case Tuple(JPEGParseTuple)
}

private static func parseJPEG(tuple: JPEGParseTuple) -> JPEGParseResult {
    let data = tuple.data
    let offset = tuple.offset
    let segment = tuple.segment

    if segment == .EOISegment
        || (data.length <= offset + 1)
        || (data.length <= offset + 2) && segment == .SkipSegment
        || (data.length <= offset + 7) && segment == .ParseSegment {
            return .Size(CGSizeZero)
    }
    switch segment {
    case .NextSegment:
        let newOffset = offset + 1
        var byte = 0x0; data.getBytes(&byte, range: NSRange(location: newOffset, length: 1))

        if byte == 0xFF {
            return .Tuple(JPEGParseTuple(data, offset: newOffset, segment: .SOFSegment))
        } else {
            return .Tuple(JPEGParseTuple(data, offset: newOffset, segment: .NextSegment))
        }
    case .SOFSegment:
        let newOffset = offset + 1
        var byte = 0x0; data.getBytes(&byte, range: NSRange(location: newOffset, length: 1))

        switch byte {
        case 0xE0...0xEF:
            return .Tuple(JPEGParseTuple(data, offset: newOffset, segment: .SkipSegment))
        case 0xC0...0xC3, 0xC5...0xC7, 0xC9...0xCB, 0xCD...0xCF:
            return .Tuple(JPEGParseTuple(data, offset: newOffset, segment: .ParseSegment))
        case 0xFF:
            return .Tuple(JPEGParseTuple(data, offset: newOffset, segment: .SOFSegment))
        case 0xD9:
            return .Tuple(JPEGParseTuple(data, offset: newOffset, segment: .EOISegment))
        default:
            return .Tuple(JPEGParseTuple(data, offset: newOffset, segment: .SkipSegment))
        }

    case .SkipSegment:
        var length = UInt16(0)
        data.getBytes(&length, range: NSRange(location: offset + 1, length: 2))

        let newOffset = offset + Int(CFSwapInt16(length)) - 1
        return .Tuple(JPEGParseTuple(data, offset: Int(newOffset), segment: .NextSegment))

    case .ParseSegment:
        var size = JPEGSize(); data.getBytes(&size, range: NSRange(location: offset + 4, length: 4))
        return .Size(CGSize(width: Int(CFSwapInt16(size.width)), height: Int(CFSwapInt16(size.height))))
    default:
        return .Size(CGSizeZero)
    }

}

private static func parseJPEGData(data: NSData, offset: Int, segment: JPEGHeaderSegment) -> CGSize {
    var tuple: JPEGParseResult = .Tuple(JPEGParseTuple(data, offset: offset, segment: segment))
    while true {
        switch tuple {
        case .Size(let size):
            return size
        case .Tuple(let newTuple):
            tuple = parseJPEG(newTuple)
        }
    }
}

[bananita]

hello @kaishin ! are you going to fix it?

[kaishin]

@bananita It might take me a while, so I'd be happy to review a PR instead to speed things up.