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Objective-C 实现 SNTP 协议
以下代码将展示如何通过 UDP 套接字与 NTP 服务器通信并获取时间。
#import <Foundation/Foundation.h>
@interface SNTPClient : NSObject
- (instancetype) initWithServerIPAddress:(NSString *)ipAddress;
- (void) fetchTime;
- (NSDate *)getTime;
- (void) dealloc;
@end
#import <sys/socket.h> #import <netinet/in.h> #import <arpa/inet.h> #import <unistd.h>
@interface SNTPClient () { CFSocketRef _socket; CFDataRef _receiveBuffer; CFStringRef _remoteHost; }
@property (nonatomic, strong) NSDate *time;
- (void)socketConfigure;
- (void)sendMessage;
- (void)readData;
- (NSDate *)getTime;
@end
@implementation SNTPClient
-
(void)socketConfigure { _socket = CFsockSocketCreate(kCFHostSocketType, SOCK_STREAM, 0, 0); CFsockSetSockName(_socket, (__bridge CFStringRef *)([self ipAddress] UTF8String)); CFsockSetSockKeepalive(_socket, 1); CFsockSetReceiveTimeout(_socket, 5); CFsockSetSendTimeout(_socket, 5); }
-
(void)sendMessage { const char *message = "SNTP Request"; int len = strlen(message) + 1; char buffer[len]; memcpy(buffer, message, len); buffer[len] = 0;
if (CFsockSendMessage(_socket, (__bridge CFStringRef *)(buffer))) { // Handle error } }
-
(void)readData { int readSize = 0; CFDataRef dataRef; const void *data = CFsockRead(_socket, 0, 1024, (unsigned char **)&dataRef, &readSize); if (data) { CFStringRef host; const char *buffer = (const char *)CFDataGetValues(dataRef)[0]; CFStringRef address; if (CFStringCreateFromCString(kCFStringEncodingASCII, buffer, &address)) { _remoteHost = (__bridge CFStringRef *)(address); } // Process the received time data [self processTimeData]; } }
-
(NSDate *)getTime { return _time; }
-
(void)processTimeData { // Parse the received time data and update the internal time // Example: Assume the time is in seconds since the epoch double seconds = ...; // Parse from the received data _time = [NSDate dateWithTimeIntervalSinceReferenceDate: seconds]; }
-
(void)dealloc { CFRelease(_socket); CFRelease(_receiveBuffer); [super dealloc]; }
@end
在 iOS 应用中，SNTP 协议可以被用来获取远程服务器的时间信息。这可以确保设备时钟与网络时间保持一致，减少时间误差。
通过上述代码示例，可以看到实现 SNTP 协议的基本思路。首先，创建一个 UDP 套接字，然后连接到指定的 NTP 服务器地址。发送一个时间请求包，接收服务器的响应数据，然后解析时间信息并更新本地时间。
这种方法在网络环境中非常有用，尤其是在需要准确时间的应用场景中。
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