C posix套接字，无法将数据从客户端发送到服务器

Question

我想创建一个客户端并将其连接到服务器。我知道客户端进程在服务器之前开始运行，所以我在无限循环中进行连接，直到它被接受。然后我想向客户端输入消息并将它们发送到服务器，服务器将它们打印在屏幕上。我从代码中删除了所有错误检测以使其更短，我知道它们必须在那里。我正在尝试这样做，但服务器什么也没收到，客户端无法进行第二次连接。

服务器

int main(int argc, char *argv[])
{
    int sockfd, newsockfd;
    socklen_t clilen;
    char buffer[256];
    struct sockaddr_in serv_addr, cli_addr;
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    serv_addr.sin_port = htons(5000);
    bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));
    listen(sockfd, 5);
    clilen = sizeof(cli_addr);
    while (newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr,&clilen) >= 0)
    {
        read(newsockfd, buffer, 255);
        close(newsockfd);
    }
    close(sockfd);
    return 0;
}

客户

int main(int argc, char *argv[])
    {
    int sockfd;
    struct sockaddr_in serv_addr;

    char buffer[256];
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    serv_addr.sin_port = htons(5000);
    while (1) {
        while ((connect(sockfd,(struct sockaddr *)  &serv_addr,sizeof(serv_addr)) < 0)) {
           printf("trying to connect\n");
           sleep(1);
        }
        printf("connected\nplease, enter a message\n");
        scanf("%s", buffer);
        write(sockfd, buffer, strlen(buffer));
    }
    close(sockfd);
    return 0;
}

Answer 1

我不知道您是如何编译代码的，但如果您设置了警告标志（gcc 中的-Wall），您会收到此警告

server.c: In function ‘main’:
server.c:33:44: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
 if (newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr,&clilen) >= 0) {

照着它，我变了，这个..

if (newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr,&clilen) >= 0) {

To ..（注意额外的括号）

if ((newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr,&clilen)) >= 0) {

我没有收到更多警告，服务器捕获了客户端的消息。

这是我在调试时运行的服务器（这基本上是您的代码稍作改动）

int sockfd, newsockfd;
socklen_t clilen;
char buffer[256];
int nbytes = 0;
struct sockaddr_in serv_addr, cli_addr;
sockfd = socket(AF_INET, SOCK_STREAM, 0);
serv_addr.sin_family = AF_INET;
//serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
serv_addr.sin_addr.s_addr = INADDR_ANY;
serv_addr.sin_port = htons(5007);
bind(sockfd, (struct sockaddr *) &serv_addr, sizeof(serv_addr));


if (listen(sockfd, 5) <0) { }

clilen = sizeof(cli_addr);
if ((newsockfd = accept(sockfd, (struct sockaddr *) &cli_addr,&clilen)) >= 0) { 

    while ((nbytes = read(newsockfd, buffer, sizeof(buffer)))<0) {
        sleep(1);
    }

    printf("client sent: %s", buffer);
}
close(newsockfd);
close(sockfd);
return 0;

Answer 2

另一个问题是我们每次在客户端连接时都必须创建套接字，例如：

while (1) {
    sockfd = socket(AF_INET, SOCK_STREAM, 0);
    while ((connect(sockfd,(struct sockaddr *)  &serv_addr,sizeof(serv_addr)) < 0)) {
       printf("trying to connect\n");
       sleep(1);
    }
    printf("connected\nplease, enter a message\n");
    scanf("%s", buffer);
     write(sockfd, buffer, strlen(buffer));
}