写一个结构文件的最佳方法是什么?

我有这两个结构：

struct pcap_hdr_s {
    UInt32 magic_number;
    UInt16 version_major;
    UInt16 version_minor;
    int32_t thiszone;
    UInt32 sigfigs;
    UInt32 snaplen;
    UInt32 network;
};
//packet header
struct pcaprec_hdr_s {
    UInt32 ts_sec;
    UInt32 ts_usec;
    UInt32 incl_len;
    UInt32 orig_len;
};

初始化如下(例如(：

    let pcapHeader : pcap_hdr_s = pcap_hdr_s(magic_number: 0xa1b2c3d4,
                                            version_major: 2, 
                                            version_minor: 4, 
                                            thiszone: 0, 
                                            sigfigs: 0,
                                            snaplen: 
                                            pcap_record_size, 
                                            network: LINKTYPE_ETHERNET)
    let pcapRecHeader : pcaprec_hdr_s = pcaprec_hdr_s(ts_sec: UInt32(ts.tv_sec),
                                        ts_usec: UInt32(ts.tv_nsec), 
                                        incl_len: plen, 
                                        orig_len: length)

我尝试创建类似结构的数据/nsdata对象：

            //write pcap header
            let pcapHeaderData : NSData = NSData(bytes: pcapHeader, length: sizeofValue(pcapHeader))
            //write pcaprec header
            let pcapRecHeaderData : NSData = NSData(bytes: pcapRecHeader, length: sizeofValue(pcapRecHeader))

，但我总是为每行的错误遇到此错误：

"Connot convert value if type 'pcap_hdr_s' to expected arguemnt type 'UsafeRawPointer?'"

我在Swift中查看了Unsaferawpointers的文档，但是我现在还没有得到足够的收益，可以从结构中创建NSDATA对象。我是正确的方式还是更好的方法可以完成我的意图？

如果此数据初始化起作用，我的下一步将是

将pcaprecheaderdata附加到pcapheaderdata
用数据/nsdata的提供功能

编辑：

//packet ethernet header
struct ethernet_hdr_s {
    let dhost : [UInt8]
    let shost : [UInt8]
    let type : UInt16
};
let src_mac : [UInt8] = [0x66, 0x77, 0x88, 0x99, 0xAA, 0xBB]
let dest_mac : [UInt8] = [0x00, 0x11, 0x22, 0x33, 0x44, 0x55]
let ethernetHeader : ethernet_hdr_s = ethernet_hdr_s(dhost: dest_mac, shost: src_mac, type: 0x0800)

编辑2：

let payloadSize = packet.payload.count
            let plen = (payloadSize < Int(pcap_record_size) ? payloadSize : Int(pcap_record_size));
            bytesWritten = withUnsafePointer(to: &(packet.payload)) {
                $0.withMemoryRebound(to: UInt8.self, capacity: Int(plen)) {
                    ostream.write($0, maxLength: Int(plen))
                }
            }
            if bytesWritten != (Int(plen)) {
                // Could not write all bytes, report error ...
                NSLog("error in Writting packet payload, not all Bytes written: bytesWritten: %d|plen: %d", bytesWritten, Int(plen))
            }

您可以将任意数据写入InputStream而不创建一个 (NS)Data对象首先。"挑战"是如何将指针转换为write方法所预期的UInt8指针的结构：

let ostream = OutputStream(url: url, append: false)! // Add error checking here!
ostream.open()
var pcapHeader = pcap_hdr_s(...)
let headerSize = MemoryLayout.size(ofValue: pcapHeader)
let bytesWritten = withUnsafePointer(to: &pcapHeader) {
        $0.withMemoryRebound(to: UInt8.self, capacity: headerSize) {
        ostream.write($0, maxLength: headerSize)
    }
}
if bytesWritten != headerSize {
    // Could not write all bytes, report error ...
}

以相同的方式可以从InputStream中读取数据：

let istream = InputStream(url: url)! // Add error checking here!
istream.open()
let bytesRead = withUnsafeMutablePointer(to: &pcapHeader) {
    $0.withMemoryRebound(to: UInt8.self, capacity: headerSize) {
        istream.read($0, maxLength: headerSize)
    }
}
if bytesRead != headerSize {
    // Could not read all bytes, report error ...
}

如果文件可能是在其他平台上创建的，则不同的字节顺序，您可以检查"魔术"并交换字节如有必要(如https://wiki.wireshark.org/development/libpcapfileformat上所述(：

switch pcapHeader.magic_number {
case 0xa1b2c3d4:
    break // Already in host byte order
case 0xd4c3b2a1:
    pcapHeader.version_major = pcapHeader.version_major.byteSwapped
    pcapHeader.version_minor = pcapHeader.version_minor.byteSwapped
    // ...
default:
    // Unknown magic, report error ...
}

简化编写和阅读结构的任务，一个人可以定义自定义扩展方法，例如

extension OutputStream {
    enum ValueWriteError: Error {
        case incompleteWrite
        case unknownError
    }
    func write<T>(value: T) throws {
        var value = value
        let size = MemoryLayout.size(ofValue: value)
        let bytesWritten = withUnsafePointer(to: &value) {
            $0.withMemoryRebound(to: UInt8.self, capacity: size) {
                write($0, maxLength: size)
            }
        }
        if bytesWritten == -1 {
            throw streamError ?? ValueWriteError.unknownError
        } else if bytesWritten != size {
            throw ValueWriteError.incompleteWrite
        }
    }
} 
extension InputStream {
    enum ValueReadError: Error {
        case incompleteRead
        case unknownError
    }
    func read<T>(value: inout T) throws {
        let size = MemoryLayout.size(ofValue: value)
        let bytesRead = withUnsafeMutablePointer(to: &value) {
            $0.withMemoryRebound(to: UInt8.self, capacity: size) {
                read($0, maxLength: size)
            }
        }
        if bytesRead == -1 {
            throw streamError ?? ValueReadError.unknownError
        } else if bytesRead != size {
            throw ValueReadError.incompleteRead
        }
    }
}

现在您可以简单地写和阅读

try ostream.write(value: pcapHeader)
try istream.read(value: &pcapHeader)

当然，这仅与像您一样的"独立"结构作用 pcap_hdr_s和pcaprec_hdr_s。

您可以将pcap_hdr_s转换为Data，反之亦然，在Swift 3中使用

pcap_hdr_s-> Data

var pcapHeader : pcap_hdr_s = pcap_hdr_s(magic_number ...
let data = withUnsafePointer(to: &pcapHeader) {
     Data(bytes: UnsafePointer($0), count: MemoryLayout.size(ofValue: pcapHeader))
}

Data-> pcap_hdr_s

let header: pcap_hdr_s = data.withUnsafeBytes { $0.pointee }

参考：往返数据类型访问/来自数据

相关内容

最新更新

热门标签：