ios - swift : LZ4 decoding with block mode

Question

我在以 block 模式解码 LZ4 编码数据时遇到了困难，并且苹果文档无法帮助我获得结果，

这是我在 iOS 12、Swift 4.1 上的代码:

let intArray: [Int8] =  [-16, 1, 1, 39, 0, 19, 11, -30, 7, 10, 29, 14, 0, 0, 0, 0, 96, 9, 6, 0, 1, 2, 0, 17, 14, 6, 0, 2, 2, 0, 18, 14, 7, 0, 65, 0, 0, 0, -51, 6, 0, 0, 2, 0, 0, 43, 0, 16, 2, 9, 0, -1, 13, 0, 0, 0, 1, 0, 0, 0, 3, 0, 0, 0, 5, 0, 0, 0, 6, 0, 0, 0, 7, 0, 0, 0, 8, 0, 0, 0, 10, 4, 0, 64, 33, -105, 58, 115, 0, 12, 2, 0, 80, 0, 0, 0, 0, 0]

            let uintArray = intArray.map { UInt8(bitPattern: $0) }

// For Visibility the uintArray unsigned is [240, 1, 1, 39, 0, 19, 11, 226, 7, 10, 29, 14, 0, 0, 0, 0, 96, 9, 6, 0, 1, 2, 0, 17, 14, 6, 0, 2, 2, 0, 18, 14, 7, 0, 65, 0, 0, 0, 205, 6, 0, 0, 2, 0, 0, 43, 0, 16, 2, 9, 0, 255, 13, 0, 0, 0, 1, 0, 0, 0, 3, 0, 0, 0, 5, 0, 0, 0, 6, 0, 0, 0, 7, 0, 0, 0, 8, 0, 0, 0, 10, 4, 0, 64, 33, 151, 58, 115, 0, 12, 2, 0, 80, 0, 0, 0, 0, 0]

            var encodedData = Data.init(bytes:uintArray)

            let decodedCapacity = 205
            let decodedDestinationBuffer = UnsafeMutablePointer<UInt8>.allocate(capacity: decodedCapacity)

            let decodedData = encodedData.withUnsafeBytes {
                (encodedSourceBuffer: UnsafePointer<UInt8>) -> Data? in

                let decodedCharCount = compression_decode_buffer(decodedDestinationBuffer,
                                                                 decodedCapacity,
                                                                 encodedSourceBuffer,
                                                                 encodedData.count,
                                                                 nil,
                                                                 COMPRESSION_LZ4)

                if decodedCharCount == 0 {
                    fatalError("Decoding failed.")
                }

                print("Before: \(encodedSourceBuffer) | After: \(decodedCharCount)")

                return Data(bytesNoCopy: decodedDestinationBuffer, count: decodedCharCount, deallocator: .free)

            }

引用来源:https://developer.apple.com/documentation/compression/compressing_and_decompressing_data_with_buffer_compression

提前致谢，这将是一个很大的帮助!

当前输出:解码失败

预期输出(以有符号字节为单位):

[1, 39, 0, 19, 11, -30, 7, 10, 29, 14, 0, 0, 0, 0, 96, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, -51, 0, 0, 0, 0, 0, 0, 0, 0, 0, 96, 9, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 3, 0, 0, 0, 5, 0, 0, 0, 6, 0, 0, 0, 7, 0, 0, 0, 8, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, -105, 58, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

预期输出(以无符号字节为单位):

[1, 39, 0, 19, 11, 226, 7, 10, 29, 14, 0, 0, 0, 0, 96, 9, 0, 0, 0, 0, 0, 0, 0, 0, 0, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 14, 0, 0, 0, 0, 0, 0, 0, 0, 0, 205, 0, 0, 0, 0, 0, 0, 0, 0, 0, 96, 9, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 3, 0, 0, 0, 5, 0, 0, 0, 6, 0, 0, 0, 7, 0, 0, 0, 8, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 10, 0, 0, 0, 151, 58, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]

Answer 1

好的，我再次对提示 Apple 文档表示歉意，

他们明确提到，

压缩 block 头由八位位组 0x62、0x76、0x34 和 0x31 组成，后跟 block 表示的解码(明文)数据的大小(以字节为单位)以及存储在中的编码数据的大小(以字节为单位) block 。 header 将两个大小字段存储为(可能未对齐)32 位小端值。实际的 LZ4 编码数据流紧跟在压缩 block 头之后。

就我而言，我不需要标题，

所以最好的常量是 COMPRESSION_LZ4_RAW ，LZ4 压缩算法，没有帧头。

将算法类型 COMPRESSION_LZ4 更改为 COMPRESSION_LZ4_RAW 解决了该问题