C UDP 客户端服务器不工作

Question

所以我有一个 UDP 服务器，它使用以下代码将小时或日期返回给客户端:

#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>
#include <time.h>

void main(int argc, char *argv[]) {
    struct addrinfo hints;
    struct addrinfo *res;
    struct sockaddr_storage cli;
    time_t rawtime;
    struct tm* timeinfo;
    char tbuffer[9];
    char buf[81], host[NI_MAXHOST], serv[NI_MAXSERV];

    hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
    hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
    hints.ai_flags = AI_PASSIVE;    /* For wildcard IP address */
    hints.ai_protocol = 0;          /* Any protocol */

    getaddrinfo(argv[1], argv[2], &hints, &res);
    int sd = socket(res->ai_family, res->ai_socktype, 0);
    bind(sd, (struct sockaddr *)res->ai_addr, res->ai_addrlen);
    freeaddrinfo(res);

    while(1) {
        socklen_t clen = sizeof(cli);
        int c = recvfrom(sd, buf, 80, 0, (struct sockaddr*) &cli, &clen);
        buf[c] = '\0';
        getnameinfo((struct sockaddr*) &cli, clen, host, NI_MAXHOST, serv, NI_MAXSERV, NI_NUMERICHOST);
        time(&rawtime);
        timeinfo = localtime(&rawtime);
        if(buf[0] == 't') {
                printf("%ld bytes de %s:%s\n", c, host, serv);
                ssize_t chars = strftime(tbuffer, sizeof(tbuffer), "%T", timeinfo);
                sendto(sd, tbuffer, chars, 0, (struct sockaddr *)&cli, clen);
        } else if(buf[0] == 'd') {
                printf("%ld bytes de %s:%s\n", c, host, serv);
                ssize_t chars = strftime(tbuffer, sizeof(tbuffer), "%D", timeinfo);
                sendto(sd, tbuffer, chars, 0, (struct sockaddr *)&cli, clen);
        } else if(buf[0] == 'q') {
                printf("Saliendo...\n");
                exit(EXIT_SUCCESS);
        } else {
                printf("Comando no soportado %s", buf);
        }
    }
}

为了测试我使用的代码 ./server <IPServerAddres> <PortAddress>在服务器端和nc -u <IpServerAddress> <PortServer>在客户端(另一台机器)。

现在我想创建 UDP 客户端 UDP 并在不使用 nc 的情况下执行相同操作, 只写 ./client <IPServerAddres> <PortAddress> <command>其中 command可以是t时间d日期和 q退出，就像在服务器中一样。

客户端程序代码如下:

#include <sys/types.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/socket.h>
#include <netdb.h>
#include <time.h>

int main(int argc, char *argv[]) {
    struct addrinfo hints;
    struct addrinfo *res, *resp;
    int sd, j, s;
    size_t len;
    ssize_t nread, nwrite;
    char buf[500];

    if (argc < 3) {
        fprintf(stderr, "Usage: %s host port command...\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    memset(&hints, 0, sizeof(struct addrinfo));
    hints.ai_family = AF_UNSPEC;    /* Allow IPv4 or IPv6 */
    hints.ai_socktype = SOCK_DGRAM; /* Datagram socket */
    hints.ai_flags = 0;
    hints.ai_protocol = 0;          /* Any protocol */

    getaddrinfo(argv[1], argv[2], &hints, &res);

    for(resp = res; resp != NULL; resp = resp->ai_next) {
        sd = socket(resp->ai_family, resp->ai_socktype, resp->ai_protocol);
        if(sd == -1) {
            perror("socket()");
            continue;
        }

        if(connect(sd, resp->ai_addr, resp->ai_addrlen) == -1) {
            perror("socket()");
        } else {
            break;
        }

        close(sd);
    }

    freeaddrinfo(res);

    for(j = 3; j < argc; j++) {
        len = strlen(argv[j]) + 1;
        nwrite = write(sd, argv[j], len);
        if(nwrite == -1) perror("write()");
        nread = read(sd, buf, 500);
        buf[nread] = 0;
        if(nread == -1) perror("read()");
        printf("Recibidos %ld bytes: %s\n", (long) nread, buf);
    }

    exit(EXIT_SUCCESS);
}

问题是，当我尝试运行我的客户端程序时，我没有得到任何响应，所以我猜是在无限循环或类似的情况下。

如有任何帮助，我将不胜感激，我正在学习 C，所以对于错误，我深表歉意，谢谢。

已编辑:更正了 break在for以防循环 connect()返回不同于 -1 的内容。

Answer 1

问题在于您计算要发送的消息的长度:

len = strlen(argv[j] + 1);

这会获取字符串的长度从第二个字符开始。你想要:

len = strlen(argv[j]) + 1;

这将为您提供字符串长度加 1 的空终止符。

此外，在阅读响应后，您需要对返回的内容进行空终止:

buf[nread] = 0;