如何发送传输时间戳和数据有效载荷？

Question

我正在尝试发送数据包的传输时间戳来计算延迟。感谢Linux, UDP datagrams, and kernel timestamps: Lots of examples and stackoversflow entries later, and still cannot get timestamps at all，我可以在发送和接收数据报时获得时间戳。但是，本条目中的demo只能在sender中获取发送时间戳，在receiver中获取接收时间戳。我想知道如何发送数据报和传输时间戳，以便在接收器中同时获得传输和接收时间戳？我已经阅读了https://www.kernel.org/doc/Documentation/networking/timestamping.txt 文档，但我没有找到可能有帮助的东西。任何人都可以对此有想法吗？

谢谢！

Answer 1

您必须将时间戳的字节存储在您的消息中（开头是最好的，最好是在您自己的标头中，以及其他重要信息）。请参见下面的示例：

客户

#include <stdio.h>      // Default System Calls
#include <stdlib.h>     // Needed for OS X
#include <string.h>     // Needed for Strlen
#include <sys/socket.h> // Needed for socket creating and binding
#include <netinet/in.h> // Needed to use struct sockaddr_in
#include <time.h>       // To control the timeout mechanism

int main( void )
{
    int fd;
    if ( (fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
        perror("socket failed");
        return 1;
    }

    struct sockaddr_in serveraddr;
    memset( &serveraddr, 0, sizeof(serveraddr) );
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_port = htons( 50037 );
    serveraddr.sin_addr.s_addr = htonl( 0x7f000001 );


    int n = (int)time(NULL);
    unsigned char timestamp[4];
    timestamp[0] = (n >> 24) & 0xFF;
    timestamp[1] = (n >> 16) & 0xFF;
    timestamp[2] = (n >> 8) & 0xFF;
    timestamp[3] = n & 0xFF;

    unsigned char buffer[256];
    memset(buffer, 0, sizeof(buffer));
    unsigned char s[6] = "hello\0";
    memcpy(&buffer, &timestamp, 4);
    memcpy(&buffer[4], &s, strlen(s));


    for ( int i = 0; i < 2; i++ ) {
        if (sendto( fd, buffer, strlen(buffer), 0, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) < 0 ) {
            perror( "sendto failed" );
            break;
        }
        printf("message sent\n" );
    }

    close( fd );
}

---

服务器

#include <stdio.h>      // Default System Calls
#include <stdlib.h>     // Needed for OS X
#include <string.h>     // Needed for Strlen
#include <sys/socket.h> // Needed for socket creating and binding
#include <netinet/in.h> // Needed to use struct sockaddr_in
#include <time.h>       // To control the timeout mechanism

int main( void )
{
    int fd;
    if ( (fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0 ) {
        perror( "socket failed" );
        return 1;
    }

    struct sockaddr_in serveraddr;
    memset( &serveraddr, 0, sizeof(serveraddr) );
    serveraddr.sin_family = AF_INET;
    serveraddr.sin_port = htons( 50037 );
    serveraddr.sin_addr.s_addr = htonl( INADDR_ANY );

    if ( bind(fd, (struct sockaddr *)&serveraddr, sizeof(serveraddr)) < 0 ) {
        perror( "bind failed" );
        return 1;
    }

    char buffer[200];
    for ( int i = 0; i < 100; i++ ) {
        int length = recvfrom( fd, buffer, sizeof(buffer) - 1, 0, NULL, 0 );
        if ( length < 0 ) {
            perror( "recvfrom failed" );
            break;
        }
        buffer[length] = '\0';
        int n = (int)time(NULL);
        int timestamp = buffer[0] << 24 | buffer[1] << 16 | buffer[2] << 8 | buffer[3]; // get the timestamp from the message

        printf( "%dsd ago - %d bytes (4 bytes for timestamp): '%s'\n", n - timestamp, length, buffer+4 );
    }

    close( fd );
}

注意：信用：https://stackoverflow.com/a/35570418/3161139 用于 UDP 服务器/客户端“hello world”

NB2：请注意，您应该在发送消息之前计算时间戳并将其 memcpy 到缓冲区，而不是在循环之前，但希望您了解总体思路

NB3：正如 chux 建议的那样，您可以避免截断：

time_t n = time(NULL); 
int len = sizeof(n);
unsigned char timestamp[len];
// fill timestamp with n

...

memcpy(&buffer, &timestamp, len);
memcpy(&buffer[len], &s, strlen(s));