Question

我有一个60字节Data流，如下所示

let myDataStream = Data(bytes: [24, 163, 209, 194, 255, 1, 184, 230, 37, 208, 140, 201, 6, 0, 64, 0, 7, 98, 108, 117, ...])

字节＃1（索引0）表示第一个对象的长度，因此在这种情况下，第一个对象由前24个对象组成，包括字节＃1

我尝试了很多方法，但我一直无法弄清楚

如何将前24个字节提取到新的数据对象
如果＃1完成后，如何从myDataStream删除前24个字节。字节＃25将再次具有下一个对象的大小

我最接近解决＃1是

let streamLength = Int(myDataStream[0])
let newStream = Data(bytes: myDataStream[0...streamLength])

但是我收到一条错误，指出cannot invoke initializer for Data with Data.subsequence

Answer 1

您可以结合使用subdata和removeSubRange方法来达到理想的效果。

subData(in:)是Data结构上的实例方法。

removeSubRange()也是Data结构上的实例方法。

您可以在此处详细了解这些方法：https://developer.apple.com/reference/foundation/data

示例方法：

func extract(from data: inout Data) -> Data? {
    guard data.count > 0 else {
        return nil
    }

    // Define the length of data to return
    let length = Int.init(data[0])

    // Create a range based on the length of data to return
    let range = Range(0..<length)

    // Get a new copy of data
    let subData = data.subdata(in: range)

    // Mutate data
    data.removeSubrange(range)

    // Return the new copy of data
    return subData
}

<强>用法：

// Data (27 bytes)
var data = Data(bytes: [24, 163, 209, 194, 255, 1, 184, 230, 37, 208, 140, 201, 6, 0, 64, 0, 7, 98, 108, 117, 42, 63, 78, 200, 3, 34, 36])

// First extraction
let first = extract(from: &data)
print(first!) // Prints 24 bytes
print(data) // Prints 3 bytes

// Second extraction
let second = extract(from: &data)
print(second!) // Prints 3 bytes
print(data) // Prints 0 bytes

// Third extraction
let third = extract(from: &data)
print(third ?? "No Data") // Prints "No Data"

进行推广

您还可以将extract方法包含在Data的扩展名中，如下所示：

extension Data {
    mutating func extract() -> Data? {
        guard self.count > 0 else {
            return nil
        }

        // Define the length of data to return
        let length = Int.init(self[0])

        // Create a range based on the length of data to return
        let range = Range(0..<length)

        // Get a new copy of data
        let subData = self.subdata(in: range)

        // Mutate data
        self.removeSubrange(range)

        // Return the new copy of data
        return subData
    }
}

然后你可以使用这样的方法：

// Data (27 bytes)
var data = Data(bytes: [24, 163, 209, 194, 255, 1, 184, 230, 37, 208, 140, 201, 6, 0, 64, 0, 7, 98, 108, 117, 42, 63, 78, 200, 3, 34, 36])

// First extraction
let first = data.extract()
print(first!) // Prints 24 bytes
print(data) // Prints 3 bytes

// Second extraction
let second = data.extract()
print(second!) // Prints 3 bytes
print(data) // Prints 0 bytes

// Third extraction
let third = data.extract()
print(third ?? "No Data") // Prints "No Data"

Answer 2

Data具有处理subdata的专用函数：

let streamLength = Int(myDataStream[0])
let newStream = myDataStream.subdata(in: 1..<streamLength + 1)
let nextStream = myDataStream.subdata(in: streamLength + 1..<myDataStream.count)

Answer 3

您可能正在寻找InputStream.

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3 个答案: