C posix套接字，无法从客户端向服务器发送数据

Question

我想制作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启动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，服务器将在屏幕上打印它们。我从代码中删除了所有错误检测以使其更短，我知道它们必须存在。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;
}

客户端

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，但是如果您设置了警告标志（gcc 中的 -Wall），您就会收到此警告

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) {

靠着它，我变了，这个..

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

至 ..（注意额外的括号）

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

我没有再收到其他警告，服务器收到了客户端的消息。

这是我调试时运行的服务器（这基本上是您的代码，略有改动）

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));
}

C posix套接字，无法从客户端向服务器发送数据

C posix sockets, can't send data from client to server

c

sockets

posix