如何在 linux 中使用 UDP 数据报发送变量？

Question

我有一个使用 UDP 的客户端和服务器： client.c:

#include<stdio.h> //printf
#include<string.h> //memset
#include<stdlib.h> //exit(0);
#include<arpa/inet.h>
#include<sys/socket.h>

#define SERVER "127.0.0.1"
#define BUFLEN 512  //Max length of buffer
#define PORT 8888   //The port on which to send data

void die(char *s)
{
    perror(s);
    exit(1);
}

int main(void)
{
    struct sockaddr_in si_other;
    int s, i, slen=sizeof(si_other);
    char buf[BUFLEN];
    char message[BUFLEN];

    if ( (s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
    {
        die("socket");
    }

    memset((char *) &si_other, 0, sizeof(si_other));
    si_other.sin_family = AF_INET;
    si_other.sin_port = htons(PORT);

    if (inet_aton(SERVER , &si_other.sin_addr) == 0) 
    {
        fprintf(stderr, "inet_aton() failed\n");
        exit(1);
    }

    while(1)
    {
        printf("Enter message : ");
        gets(message);

        //send the message
        if (sendto(s, message, strlen(message) , 0 , (struct sockaddr *) &si_other, slen)==-1)
        {
            die("sendto()");
        }

        //receive a reply and print it
        //clear the buffer by filling null, it might have previously received data
        memset(buf,'[=11=]', BUFLEN);
        //try to receive some data, this is a blocking call
        if (recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *) &si_other, &slen) == -1)
        {
            die("recvfrom()");
        }

        puts(buf);
    }

    close(s);
    return 0;
}

当然还有我的服务器：

#include<stdio.h> //printf
#include<string.h> //memset
#include<stdlib.h> //exit(0);
#include<arpa/inet.h>
#include<sys/socket.h>

#define BUFLEN 512  //Max length of buffer
#define PORT 8888   //The port on which to listen for incoming data

void die(char *s)
{
    perror(s);
    exit(1);
}

int main(void)
{
    struct sockaddr_in si_me, si_other;

    int s, i, slen = sizeof(si_other) , recv_len;
    char buf[BUFLEN];

    //create a UDP socket
    if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
    {
        die("socket");
    }

    // zero out the structure
    memset((char *) &si_me, 0, sizeof(si_me));

    si_me.sin_family = AF_INET;
    si_me.sin_port = htons(PORT);
    si_me.sin_addr.s_addr = htonl(INADDR_ANY);

    //bind socket to port
    if( bind(s , (struct sockaddr*)&si_me, sizeof(si_me) ) == -1)
    {
        die("bind");
    }

    //keep listening for data
    while(1)
    {
        printf("Waiting for data...");
        fflush(stdout);
    memset(buf,'[=12=]',BUFLEN);         
        //try to receive some data, this is a blocking call
        if ((recv_len = recvfrom(s, buf, BUFLEN, 0, (struct sockaddr *) &si_other, &slen)) == -1)
        {
            die("recvfrom()");
        }

        //print details of the client/peer and the data received
        printf("Received packet from %s:%d\n", inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port));
        printf("Data: %s\n" , buf);

        //now reply the client with the same data
        if (sendto(s, buf, recv_len, 0, (struct sockaddr*) &si_other, slen) == -1)
        {
            die("sendto()");
        }
    }

    close(s);
    return 0;
}

此代码运行良好。但是，我只想使用 UDP 发送一条消息。如果有一些变量，例如：int、int、string、int。如何隐藏到 buf 以及更重要的事情 - 如何在服务器中接收变量？

Answer 1

因为系统在二进制类型的细节上可能不同（例如，小端与大端、int 的大小、结构的填充、空指针值等）a应该使用在传输过程中保留类型语义的协议。这可以通过使用一种众所周知的语义保留协议（例如，XDR https://en.wikipedia.org/wiki/External_Data_Representation, Google's protobuf https://en.wikipedia.org/wiki/Protocol_Buffers）或通过手动将类型编码为可移植格式（例如，将所有类型在发送方和在接收方将它们解析回二进制值）。

如何在 linux 中使用 UDP 数据报发送变量？

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