C 回显服务器，回显一个句子后不能正常工作

Question

在测试这段代码时，我发现这个回显服务器对一个词工作得很好。如果尝试回显一个句子，服务器也会回显它，但在那之后它会回显输入与前一个回显句子的最后一个词。我使用 memset 清除了缓冲区，但仍然遇到同样的问题。无法理解问题出在哪里。

服务器代码

#include<stdio.h>
#include<string.h>  //strlen
#include<sys/socket.h>
#include<arpa/inet.h>   //inet_addr
#include<unistd.h>  //write

int main(int argc , char *argv[])
{
    int socket_desc , client_sock , c , read_size;
    struct sockaddr_in server , client;
    char client_message[2000];

    //Create socket
    socket_desc = socket(AF_INET , SOCK_STREAM , 0);
    if (socket_desc == -1)
    {
        printf("Could not create socket");
    }
    puts("Socket created");

    //Prepare the sockaddr_in structure
    server.sin_family = AF_INET;
    server.sin_addr.s_addr = INADDR_ANY;
    server.sin_port = htons( 8888 );

    //Bind
    if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
    {
        //print the error message
        perror("bind failed. Error");
        return 1;
    }
    puts("bind done");

    //Listen
    listen(socket_desc , 3);

    //Accept and incoming connection
    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);

    //accept connection from an incoming client
    client_sock = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c);
    if (client_sock < 0)
    {
        perror("accept failed");
        return 1;
    }
    puts("Connection accepted");

    //Receive a message from client
    memset(client_message, 0, sizeof(client_message));
    while( (read_size = recv(client_sock , client_message , 2000 , 0)) > 0 )
    {


        //Send the message back to client
        write(client_sock , client_message , strlen(client_message));
        memset(client_message, 0, sizeof(client_message));
    }

    if(read_size == 0)
    {
        puts("Client disconnected");
        fflush(stdout);
    }
    else if(read_size == -1)
    {
        perror("recv failed");
    }

    return 0;
}

客户端代码:

#include<stdio.h>   
#include<string.h>  
#include<sys/socket.h>  
#include<arpa/inet.h>   

int main(int argc , char *argv[])
{
    int sock;
    struct sockaddr_in server;
    char message[1000] , server_reply[2000];

    //Create socket
    sock = socket(AF_INET , SOCK_STREAM , 0);
    if (sock == -1)
    {
        printf("Could not create socket");
    }
    puts("Socket created");

    server.sin_addr.s_addr = inet_addr("127.0.0.1");
    server.sin_family = AF_INET;
    server.sin_port = htons( 8888 );

    //Connect to remote server
    if (connect(sock , (struct sockaddr *)&server , sizeof(server)) < 0)
    {
        perror("connect failed. Error");
        return 1;
    }

    puts("Connected\n");

    //keep communicating with server
    while(1)
    {
        printf("Enter message : ");
        //scanf("%s" , message);
    fgets(message, sizeof(message), stdin);

        //Send some data
        if( send(sock , message , strlen(message) , 0) < 0)
        {
            puts("Send failed");
            return 1;
        }

        //Receive a reply from the server
        if( recv(sock , server_reply , 2000 , 0) < 0)
        {
            puts("recv failed");
            break;
        }

        puts("Server reply :");
        puts(server_reply);

    memset(message, 0, sizeof(message));
    memset(server_reply, 0, sizeof(server_reply));
    }

    close(sock);
    return 0;
}

示例输出

Enter message : sample
Server reply :
sample

Enter message : sample test
Server reply :
sample test

Enter message : gamer
Server reply :
gamer
 test

Enter message : pro       
Server reply :
pro
r
 test

Answer 1

你的问题是这一行:

write(client_sock , client_message , strlen(client_message));

您的客户端不发送 \0 终止符。因此，如果您首先发送一个长字符串，然后发送一个短字符串，那么短字符串将只覆盖开头。将其更改为:

write(client_sock , client_message , read_size); // send exactly as much as you got

并且在客户端只打印收到的数量:

ssize_t answer_size;
if((answer_size = recv(sock , server_reply , sizeof(server_reply) , 0)) < 0)
{
    puts("recv failed");
    break;
}

printf("Server reply :\n%.*s\n", answer_size, server_reply);

另外请记住，由于具体实现原因，您可能会或不会收到第一个 recv 发送的所有内容，建议在 while 中运行它循环(必要时使用非阻塞模式)。 send 也是如此。