通过AVMetadataMachineReadableCodeObject从Aztec条形码读取原始字节会产生意外结果

Question

我一直在研究iOS阅读器应用程序,用于德国铁路(德国铁路)使用的特殊条形码.它是Aztec条形码的变体,用于连接DSA签名字符串和zlib缩减的有效负载.

我被困住了,当我得知AVMetadataMachineReadableCodeObject没有公共方法来读取条形码中包含的原始字节时,字符串方法总是使zlib压缩数据乱码.

幸运的是,这个答案让我朝着正确的方向前进.可以使用KVO访问(私有)字节,因为我目前不希望在App Store上分发应用程序,这是完美的.

尽管我几乎不存在Swift和Objective-C知识,我设法让这个工作,你可以在示例代码中看到.但是条形码中存储的字节NSData与预期结果不符!我怀疑我使用的zlib库(DeflateSwift)无法正常工作,所以我构建了一个测试用例,工作正常.

我的问题是:我做错了什么？我是否需要进一步处理原始字节以获得预期结果(见下文)？如何生究竟是存储在字节AVMetadataMachineReadableCodeObject？谁能指出我正确的方向？任何帮助表示赞赏.

这是我的代码(这是一个悲伤的mashup Swift和Objective-C)

if let metadataObject = metadataObjects.first {
    let readableObject = metadataObject as! AVMetadataMachineReadableCodeObject;
    let rawReadableObject = readableObject.valueForKeyPath("_internal.basicDescriptor")!["BarcodeRawData"] as? NSData;

    if let rawBytes = rawReadableObject {
       let barcodeData = rawBytes; // or use testData instead

        let barcodeSplit:Int = 68;
        let barcodeLength:Int = barcodeData.length;
        let barcodeHeader:NSData = barcodeData.subdataWithRange(NSRange(location: 0, length: barcodeSplit))
        let barcodeZlibContent:NSData = barcodeData.subdataWithRange(NSRange(location: barcodeSplit, length: (barcodeLength-barcodeSplit)))

        let count = barcodeZlibContent.length / sizeof(UInt8)
        var array = [UInt8](count: count, repeatedValue: 0)
        barcodeZlibContent.getBytes(&array, length:count * sizeof(UInt8))

        print("\(barcodeLength)kb")
        print(barcodeHeader)
        print(barcodeZlibContent)

        var inflater = InflateStream()
        var (inflated, err) = inflater.write(array, flush: true)
        if err != nil{
            fatalError("\(err!)")
        }

        if let ticketString = String(bytes: inflated, encoding: NSUTF8StringEncoding) {
            print(ticketString)
        } else {
            print("not a valid UTF-8 sequence")
        }
    }
}

这就是我得到的

返回的字节AVMetadataMachineReadableCodeObject是

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

这是我用于测试的Deutsche Bahn票的示例条形码.

这就是我需要的

使用正确的条形码阅读器(我使用bcTester 5)进行扫描时,会产生以下字节:

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

如您所见,在偏移量68(78 9C)处开始有效的zlib流.如果您在此处拆分数据并为zlib数据充气,它将返回如下字符串:

U_HEAD01005300802P9QAN-40501201514560DEDE0080ID0200180104840080BL020357031204GW3HEMP906012015060120151021193517S0010018Fernweh-Ticket natS00200012S0030001AS00900051-0-0S01200010S0140002S2S0150006BerlinS0160011NeumünsterS0210038B-Hbf 8:16 ICE794/HH-Hbf 10:16 IC2224S0230013Krull AndreaS026000213S0270019***************0484S0280013Andrea#Krull S031001006.01.2015S032001006.01.2015S035000511160S0360003271

测试NSData

如果我使用从bcTester返回的字节手动构建字节数组,一切都按预期工作,并且zlib数据正确膨胀.这是我测试的方式:

let testArray = [UInt8](arrayLiteral: 0x23, 0x55, 0x54, 0x30, 0x31, 0x30, 0x30, 0x38, 0x30, 0x30, 0x30, 0x30, 0x30, 0x31, 0x30, 0x2C, 0x02, 0x14, 0x1C, 0x3D, 0xE9, 0x2D, 0xCD, 0x5E, 0xC4, 0xC0, 0x56, 0xBD, 0xAE, 0x61, 0x3E, 0x54, 0xAD, 0xA1, 0xB3, 0x26, 0x33, 0xD2, 0x02, 0x14, 0x40, 0x75, 0x03, 0xD0, 0xCF, 0x9C, 0xC1, 0xF5, 0x70, 0x58, 0xBD, 0x59, 0x50, 0xA7, 0xAF, 0xC5, 0xEB, 0x0A, 0xF4, 0x74, 0x00, 0x00, 0x00, 0x00, 0x30, 0x32, 0x37, 0x31, 0x78, 0x9C, 0x65, 0x50, 0xCB, 0x4E, 0xC3, 0x30, 0x10, 0xE4, 0x53, 0x2C, 0x71, 0x43, 0x4A, 0xD9, 0xF5, 0x2B, 0x36, 0xB7, 0x84, 0x04, 0x52, 0x01, 0x55, 0x51, 0x40, 0x1C, 0x51, 0x01, 0x23, 0x2A, 0x42, 0x0E, 0x21, 0x15, 0x3F, 0xC7, 0x8D, 0x1F, 0x63, 0x36, 0x11, 0x52, 0x2B, 0x7C, 0xF1, 0x78, 0x76, 0x76, 0x66, 0xBD, 0xF7, 0x8F, 0x4D, 0x5D, 0x54, 0xC4, 0x44, 0xCE, 0x10, 0x05, 0xD2, 0xEB, 0x78, 0x5B, 0xAC, 0x32, 0x7B, 0xB4, 0x77, 0xC8, 0x11, 0x6B, 0x62, 0xC7, 0xD6, 0x79, 0xAA, 0xEA, 0xAA, 0x16, 0xE1, 0xB2, 0x22, 0x4D, 0xC4, 0x01, 0xAD, 0x36, 0x58, 0x61, 0xCA, 0x6B, 0x30, 0xC6, 0xE5, 0x64, 0xA0, 0xB6, 0x97, 0x0F, 0xA6, 0xA9, 0x6F, 0xD6, 0x71, 0xDF, 0xC7, 0xCF, 0x3E, 0x7F, 0x37, 0x93, 0x66, 0x8E, 0xC6, 0x71, 0xDE, 0x92, 0x4C, 0xC0, 0xE1, 0x22, 0x0D, 0xFD, 0x57, 0x7A, 0xCB, 0xEE, 0xB6, 0xCF, 0xEF, 0x69, 0x54, 0xFD, 0x66, 0x44, 0x05, 0x31, 0xD0, 0x03, 0x18, 0x01, 0x05, 0x40, 0x04, 0x70, 0x9C, 0x51, 0x46, 0xAD, 0x38, 0x49, 0x33, 0x00, 0x86, 0x20, 0xDD, 0x42, 0x88, 0x04, 0x22, 0x5F, 0xA6, 0xA1, 0xDB, 0xF6, 0x78, 0x79, 0xD4, 0x79, 0x95, 0x76, 0x1F, 0x3F, 0xDF, 0xFD, 0xE7, 0x98, 0x86, 0x16, 0xB1, 0x30, 0x0B, 0x65, 0xD6, 0x3C, 0xBD, 0x2A, 0x15, 0xCE, 0xD8, 0xAB, 0xE5, 0x79, 0x9D, 0x47, 0x7B, 0xDA, 0x34, 0x13, 0xC7, 0x34, 0x73, 0x5A, 0x6B, 0x0B, 0x35, 0x72, 0xD9, 0x5C, 0x0D, 0xBB, 0xAE, 0x53, 0xAA, 0xE8, 0x5F, 0x86, 0xB4, 0x01, 0xE9, 0x25, 0x8D, 0x0D, 0x50, 0x8E, 0x72, 0x3C, 0x39, 0x3C, 0xB2, 0x13, 0x94, 0x82, 0x74, 0xCE, 0x2D, 0xC7, 0xB3, 0x41, 0x8B, 0xED, 0x4C, 0x9F, 0xF5, 0x0B, 0xE2, 0x85, 0x6C, 0x01, 0x8C, 0xFE, 0xC7, 0xB8, 0xE9, 0x87, 0x8C, 0xD9, 0xF1, 0x90, 0x28, 0xA3, 0x73, 0xFE, 0x05, 0x6D, 0xDE, 0x5F, 0xF1)
let testData = NSData(bytes: testArray, length: testArray.count)

Answer 1

我前段时间在 Xamarin/C# 中解决了这个问题，但这个想法对于 Swift 来说也是一样的。和encodedData方法ReadCode取自 ZXing lib。希望能帮助到你。

它对于读取和解码“小”和“大”票证代码都很有效，但 iOS SDK 中默认的 Aztec 阅读器不够好，所以最后我们继续使用 Manateeworks 的阅读器。我现在可以看到，使用 iOS 10 SDK 并没有得到任何改善。

    public override void DidOutputMetadataObjects (AVCaptureMetadataOutput captureOutput, AVMetadataObject[] metadataObjects, AVCaptureConnection connection)
    {
        foreach (AVMetadataMachineReadableCodeObject metadata in metadataObjects) {
            var d1 = (metadata.ValueForKey ((NSString)"_internal"));
            var d2 = (d1.ValueForKey ((NSString)"basicDescriptor"));
            var data = (d2.ValueForKey ((NSString)"BarcodeRawData"));
            var str = data.ToString ().Trim ().Trim (new [] { '<', '>' }).Replace (" ", "");


            var bitarray = new bool[str.Length * 4];
            for (var i = 0; i < str.Length / 2; i++) {
                int value = Convert.ToInt32 (str.Substring (i * 2, 2), 16);
                bitarray [i * 8 + 0] = (value & 1) > 0;
                bitarray [i * 8 + 1] = (value & 2) > 0;
                bitarray [i * 8 + 2] = (value & 4) > 0;
                bitarray [i * 8 + 3] = (value & 8) > 0;
                bitarray [i * 8 + 4] = (value & 16) > 0;
                bitarray [i * 8 + 5] = (value & 32) > 0;
                bitarray [i * 8 + 6] = (value & 64) > 0;
                bitarray [i * 8 + 7] = (value & 128) > 0;
            }
            var pabData = encodedData (bitarray);

            parent.scanFinished (true, pabData);
        }
    }


    enum ZXAztecTable
    {
        ZXAztecTableUpper,
        ZXAztecTableBinary,
        ZXAztecTableDigit
    };

    public byte[] encodedData (bool[] bitArray)
    {
        var result = new List<byte> ();
        int endIndex = bitArray.Length;
        ZXAztecTable latchTable = ZXAztecTable.ZXAztecTableUpper; // table most recently latched to
        ZXAztecTable shiftTable = ZXAztecTable.ZXAztecTableUpper; // table to use for the next read
        int index = 0;
        while (index < endIndex) {
            if (shiftTable == ZXAztecTable.ZXAztecTableBinary) {
                if (endIndex - index < 5) {
                    break;
                }
                int length = ReadCode (bitArray, index, 5);
                index += 5;
                if (length == 0) {
                    if (endIndex - index < 11) {
                        break;
                    }

                    length = ReadCode (bitArray, index, 11) + 31;
                    index += 11;
                }
                for (int charCount = 0; charCount < length; charCount++) {
                    if (endIndex - index < 8) {
                        index = endIndex;  // Force outer loop to exit
                        break;
                    }

                    byte code = (byte)ReadCode (bitArray, index, 8);
                    result.Add (code);
                    index += 8;
                }
                // Go back to whatever mode we had been in
                shiftTable = latchTable;
            } else {
                int size = shiftTable == ZXAztecTable.ZXAztecTableDigit ? 4 : 5;
                if (endIndex - index < size) {
                    break;
                }
                ReadCode (bitArray, index, size);
                index += size;
                latchTable = shiftTable;
                shiftTable = ZXAztecTable.ZXAztecTableBinary;
            }
        }
        return result.ToArray ();
    }

    public int ReadCode (bool[] bitArray, int startIndex, int length)
    {
        int res = 0;
        for (int i = startIndex; i < startIndex + length; i++) {
            res <<= 1;
            if (bitArray [i]) {
                res |= 0x01;
            }
        }
        return res;
    }