如何用字符串解析Hex，Float

Question

我有二进制文件，其中包含地点和坐标（纬度，经度）的名称，每当我使用编码String将其解析为.ascii时，它都不会很好地解析它。我假设从Float值（坐标）解析失败。

阅读InputStream

extension Data {
    init(reading input: InputStream) {
        self.init()
        input.open()

        let bufferSize = 1024
        let buffer = UnsafeMutablePointer<UInt8>.allocate(capacity: bufferSize)
        while input.hasBytesAvailable {
            let read = input.read(buffer, maxLength: bufferSize)
            self.append(buffer, count: read)
        }
        buffer.deallocate()

        input.close()
    }
}

File to parse

let filepath = Bundle.main.path(forResource: "MN", ofType: "dat")
let data = Data.init(reading: InputStream(fileAtPath: filepath)!)
let parsedData = String.init(data: data, encoding: .ascii)

任何想法我怎么能以正确的方式解析它？

例如，Java ObjectInputStream具有名为：

的方法

inputStreamObj.readUTF()
inputStreamObj.readFloat()

爪哇

Answer 1

正如我在评论中所写，您需要阅读规范Object Serialization Stream Protocol。

因此，前4个字节表示STREAM_MAGIC，STREAM_VERSION，预计始终为相同的值。 5字节序列0x7A 0xhh 0xhh 0xhh 0xhh表示TC_BLOCKDATALONG（0xhhhhhhhh）。

在解析字符串和浮点数之前，需要连接所有块。

所以，准备DataReader：

（与Sulthan's几乎相同，但这正确地对待了修改后的UTF-8。）

struct DataReader {
    enum DataReaderError: Error {
        case invalidFirstByte(byte: UInt16, offset: Int)
        case invalidFollowingByte
        case missingFollowingByte
        case insufficientData
    }
    var data: Data
    var currentPosition: Int

    init(data: Data) {
        self.data = data
        self.currentPosition = 0
    }

    mutating func skipBytes(_ n: Int) {
        currentPosition += n
    }

    private mutating func readBigEndian<T: FixedWidthInteger>() throws -> T {
        guard currentPosition + MemoryLayout<T>.size <= data.count else {
            throw DataReaderError.insufficientData
        }
        var fixedWithInteger: T = 0
        let range: Range<Int> = currentPosition ..< currentPosition + MemoryLayout<T>.size
        withUnsafeMutableBytes(of: &fixedWithInteger) {ptrT in
            let uint8Ptr = ptrT.baseAddress!.assumingMemoryBound(to: UInt8.self)
            data.copyBytes(to: uint8Ptr, from: range)
        }
        currentPosition += MemoryLayout<T>.size
        return fixedWithInteger.bigEndian
    }

    mutating func readFloat() throws -> Float {
        let floatBits: UInt32 = try readBigEndian()
        return Float(bitPattern: floatBits)
    }

    mutating func readUnsignedShort() throws -> Int {
        let ushortValue: UInt16 = try readBigEndian()
        return Int(ushortValue)
    }

    mutating func readInt() throws -> Int {
        let intValue: Int32 = try readBigEndian()
        return Int(intValue)
    }

    mutating func readUnsignedByte() throws -> Int {
        guard currentPosition < data.count else {
            throw DataReaderError.insufficientData
        }
        let byte = data[currentPosition]
        currentPosition += 1
        return Int(byte)
    }

    mutating func readBytes(_ n: Int) throws -> Data {
        guard currentPosition + n <= data.count else {
            throw DataReaderError.insufficientData
        }
        let subdata = data[currentPosition ..< currentPosition+n]
        currentPosition += n
        return subdata
    }

    mutating func readUTF() throws -> String {
        //Get byte size of the string
        let count = try readUnsignedShort()
        //Decoding Modified UTF-8
        var utf16: [UInt16] = []
        var offset = 0
        while offset < count {
            let firstByte = UInt16(data[currentPosition + offset])
            if firstByte & 0b1_0000000 == 0b0_0000000 {
                utf16.append(firstByte)
                offset += 1
            } else if firstByte & 0b111_00000 == 0b110_00000 {
                guard offset + 1 < count else {throw DataReaderError.missingFollowingByte}
                let secondByte = UInt16(data[currentPosition + offset + 1])
                guard secondByte & 0b11_000000 == 0b10_000000 else {throw DataReaderError.invalidFollowingByte}
                let codeUnit = ((firstByte & 0b000_11111) << 6) | (secondByte & 0b00_111111)
                utf16.append(codeUnit)
                offset += 2
            } else if firstByte & 0b1111_0000 == 0b1110_0000 {
                guard offset + 2 < count else {throw DataReaderError.missingFollowingByte}
                let secondByte = UInt16(data[currentPosition + offset + 1])
                guard secondByte & 0b11_000000 == 0b10_000000 else {throw DataReaderError.invalidFollowingByte}
                let thirdByte = UInt16(data[currentPosition + offset + 2])
                guard thirdByte & 0b11_000000 == 0b10_000000 else {throw DataReaderError.invalidFollowingByte}
                let codeUnit = ((firstByte & 0b0000_1111) << 12) | ((secondByte & 0b00_111111) << 6) | (thirdByte & 0b00_111111)
                utf16.append(codeUnit)
                offset += 3
            } else {
                throw DataReaderError.invalidFirstByte(byte: firstByte, offset: currentPosition+offset)
            }
        }
        currentPosition += offset
        return String(utf16CodeUnits: &utf16, count: utf16.count)

    }

    var isAtEnd: Bool {
        return currentPosition == data.count
    }
}

我们可以按如下方式解析您的MN.dat：

let mnUrl = Bundle.main.url(forResource: "MN", withExtension: "dat")!
do {
    let data = try Data(contentsOf: mnUrl)
    var reader = DataReader(data: data)
    reader.skipBytes(4)

    //First collect all blocks
    var blockData = Data()
    while !reader.isAtEnd {
        let contentType = try reader.readUnsignedByte()
        if contentType == 0x7A {//TC_BLOCKDATALONG
            let size = try reader.readInt()
            let block = try reader.readBytes(size)
            blockData.append(block)
        } else if contentType == 0x77 {//TC_BLOCKDATA
            let size = try reader.readUnsignedByte()
            let block = try reader.readBytes(size)
            blockData.append(block)
        } else {
            print("Unsupported content type")
            break
        }
    }
    //Then read the contents of blockData
    var blockReader = DataReader(data: blockData)
    while !blockReader.isAtEnd {
        let string = try blockReader.readUTF()
        print(string)
        let float1 = try blockReader.readFloat()
        print(float1)
        let float2 = try blockReader.readFloat()
        print(float2)
        //Use string, float1, float2 as you like
    }
} catch {
    print(error)
}

输出：

Albert Lea
43.648
-93.3683
Albertville
45.2377
-93.6544
Alexandria
45.8852
-95.3775
(... no errors...)
Woodbury
44.9239
-92.9594
Worthington
43.62
-95.5964
Wyoming
45.3364
-92.9972
Zimmerman
45.4433
-93.59

如果您的二进制数据可能包含其他内容类型，则可能需要修改上述代码。

Answer 2

我将向您展示如何解析Java编码的数据。但是，由于我无法理解文件的格式，因此响应将不完整：

首先，加载文件：

// load the file
let fileUrl = URL(fileURLWithPath: "/Users/sulthan/Downloads/MN.dat")
let data = try! Data(contentsOf: fileUrl)

其次，创建一个简单的Java数据读取器：

// create a simple data reader
class Reader {
    let data: Data
    private var offset = 0

    init(data: Data) {
        self.data = data
    }

    var hasMoreData: Bool {
        return offset < data.count
    }

    func skip(length: Int) {
        offset += length
    }

    func readByte() -> UInt8 {
        defer { offset += 1}
        return data[offset]
    }

    // java bytes are unsigned
    func readJavaByte() -> Int8 {
        return Int8(bitPattern: readByte())
    }

    func readBytes(length: Int) -> Data {
        defer { offset += length }
        return data.subdata(in: offset ..< offset + length)
    }

    private func readJavaUShort() -> UInt16 {
        let byte1 = UInt16(exactly: readByte())!
        let byte2 = UInt16(exactly: readByte())!

        return (byte1 << 8) | byte2
    }

    func readJavaShort() -> Int16 {
        return Int16(bitPattern: readJavaUShort())
    }

    // Java UTF-8 encodes the length as first two bytes (unsigned java short)
    func readJavaUtf() -> String? {
        let length = readJavaUShort()
        let data = readBytes(length: Int(length))
        return String(data: data, encoding: .utf8)
    }

    private func readUInt32() -> UInt32 {
        let short1 = UInt32(exactly: readJavaUShort())!
        let short2 = UInt32(exactly: readJavaUShort())!

        return (short1 << 16) | short2
    }

    func readJavaInt() -> Int32 {
        let short1 = Int32(exactly: readJavaShort())!
        let short2 = Int32(exactly: readJavaShort())!

        return (short1 << 16) | short2
    }

    // interpret the 4 bytes as a floating point number
    func readJavaFloat() -> Float {
        let bits = readUInt32()
        return Float(bitPattern: bits)
    }
}

第三，解析数据。由于数据格式未知，我不能完全做到这一点：

// create a reader from our data
let reader = Reader(data: data)

// some data I don't understand
reader.skip(length: 4)

var offset = 0
while reader.hasMoreData {
    // some data I don't understand in the beginning and after every 52 items
    if offset % 53 == 0 {
        reader.skip(length: 5)
    }

    print(reader.readJavaUtf())
    print(reader.readJavaFloat())
    print(reader.readJavaFloat())

    offset += 1
}

在解析某些项目后，数据解析将与提供的数据一起崩溃。我假设您知道如何处理，因为您知道格式。