编写要文件的结构的最佳方法是什么？
编写要文件的结构的最佳方法是什么？
提问于 2017-06-04 17:15:17
我有两种结构：
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) 我尝试创建如下结构的数据/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))但我总是会得到每一行的错误：
"Connot convert value if type 'pcap_hdr_s' to expected arguemnt type 'UsafeRawPointer?'"我看了一下Swift中的UnsafeRawPointers文档，但目前还不足以从结构中创建NSData对象。我是在正确的道路上，还是有更好的方式来完成我的意愿？
如果这个数据初始化工作，我的下一步将是
- 将pcapRecHeaderData附加到pcapHeaderData
- 用数据/NSData提供的函数将pcapHeaderData原子地写入文件/url
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))
}回答 2
Stack Overflow用户
回答已采纳
发布于 2017-06-04 18:11:05
您可以将任意数据写入InputStream，而无需首先创建(NS)Data对象。“挑战”是如何按照UInt8方法的预期将指向结构的指针转换为write指针：
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 ...
}以同样的方式从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 ...
}如果文件可能是在具有不同字节顺序的不同平台上创建的，那么您可以在必要时检查“魔术”和交换字节(如https://wiki.wireshark.org/Development/LibpcapFileFormat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 ...
}为了简化写入和读取结构的任务，可以定义自定义扩展方法。
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，您可以简单地用
try ostream.write(value: pcapHeader)
try istream.read(value: &pcapHeader) 当然，这只适用于像pcap_hdr_s和pcaprec_hdr_s这样的“独立”结构。
Stack Overflow用户
发布于 2017-06-04 17:36:28
您可以在Swift 3中将pcap_hdr_s转换为Data，反之亦然
pcap_hdr_s->DatapcapHeader : pcap_hdr_s = pcap_hdr_s(magic_number .设data = withUnsafePointer(to：&pcapHeader) {Data(字节: UnsafePointer($0)，count: MemoryLayout.size(ofValue: pcapHeader)) }}Data->pcap_hdr_s让标题: pcap_hdr_s = data.withUnsafeBytes {$0.point}
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/44356770
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