c - 无法显示或recv()客户端缓冲区中的数据

Question

我正在尝试从服务器端的文件/tmp/k 读取数据并将数据复制到消息并发送到客户端。在这里，我可以将数据发送到客户端，但我的客户端无法 recv() 或显示数据。任何人都可以帮我解决这个问题，或者可以提出更好的解决方案来在客户端显示数据。

谢谢

客户端.c

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h> 
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <sys/syscall.h>

#define MAX_SIZE 100000
#define NUM_CLIENT 5
void *connection_handler(void *);

int main(int argc , char *argv[])
{
   int sockfd;
   long i;
   pthread_t sniffer_thread;
   printf("memory allocated for the creation of socket \n");
   for (i=1; i<=NUM_CLIENT; i++) {
        if( pthread_create( &sniffer_thread , NULL ,  connection_handler , (void *) i) < 0)
    {
        perror("could not create thread");
        return 1;
    } 
    printf("Thread created \n");
    sleep(2); 
} 
pthread_exit(NULL);
return 0;
}
void *connection_handler(void *threadid)
{   
    long etid; /*each thread id */
    etid = (long)threadid;
    pthread_t tid;
    tid = pthread_self();
    int sockfd;
    struct sockaddr_in serv_addr;
    char sbuff[MAX_SIZE] , rbuff[MAX_SIZE];                             
    if((sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0){
    printf("Failed creating socket\n");
    perror("could not create thread");
    return 0;
    }
    memset(&serv_addr, 0 , sizeof (serv_addr));
    printf("the bytes of memory area pointed by serv_addr is filled with constant '0' \n");
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = inet_addr("127.0.0.1");
    serv_addr.sin_port = htons(8888);

    if (connect(sockfd, (struct sockaddr *)&serv_addr, sizeof (serv_addr)) < 0) {
         perror("Failed to connect to server. Error");
         return 0;
         }
    printf("Connected successfully client:%ld \n", tid);
    printf("before calling pthread_create getpid: %d getpthread_self: %lu tid:%lu\n",getpid(), pthread_self(), syscall(SYS_gettid)); 
    while(1)
    {
       printf("For thread : %ld\n", etid);
       printf("thread id given by kernel: %ld\n", tid);
       fgets(sbuff, MAX_SIZE , stdin);
       send(sockfd,sbuff,strlen(sbuff),0);

        if(recv(sockfd,rbuff,MAX_SIZE,0)==0)
           printf("Error");
       else
          fputs(rbuff,stdout);
       bzero(rbuff,MAX_SIZE);
       sleep(2);
       } 
       close(sockfd);
       return 0;
}

服务器.c

 #include <stdio.h>
 #include <string.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <arpa/inet.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <pthread.h>
 #include <sys/syscall.h>
 #include<pthread.h> //for threading , link with lpthread
 #include <fcntl.h>

 #define PROCESSLIST "/tmp/k"
 void *connection_handler(void *);
 int main(int argc , char *argv[])
 {
     int sockfd , new_socket , c , *new_sock;
     struct sockaddr_in server , client;
     char *message;

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

     //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(sockfd,(struct sockaddr *)&server , sizeof(server)) < 0)
    {
       puts("bind failed");
       return 1;
     }
     puts("bind done");

     //Listen
     listen(sockfd , 3);

    //Accept and incoming connection
    puts("Waiting for incoming connections...");
    c = sizeof(struct sockaddr_in);
    while( (new_socket = accept(sockfd, (struct sockaddr *)&client, (socklen_t*)&c)) )
    {
        puts("Connection accepted");

        pthread_t sniffer_thread;
        new_sock = malloc(1);
       *new_sock = new_socket;

      if( pthread_create( &sniffer_thread , NULL ,  connection_handler , (void*) new_sock) < 0)
      {
        perror("could not create thread");
        return 1;
       }
    puts("Handler assigned");
   }

   if (new_socket<0)
   {
    perror("accept failed");
    return 1;
    }

    return 0;
}

  /* This will handle connection for each client */
void *connection_handler(void *sockfd)
{
       //Get the socket descriptor
      int sock = *(int*)sockfd;
      int read_size;
      char message[100000], client_message[2000];
      int fd;
      void *buff;
      //Receive a message from client
     while( (read_size = recv(sock , client_message , 2000 , 0)) > 0 )
     {
        system ("ps -ef > /tmp/k");
        puts("temp file getting created");
        fd = open (PROCESSLIST, O_RDONLY);
        puts("file open has taken place");
        read(fd, buff, sizeof(*buff));
        puts("reading the file");
        write(sock, buff, 1);
        puts("writing to the buffer");
        puts("copied data from buffer to message");
        //Send the message back to client
        send(sock,message,strlen(message),0);
        puts("data has been sent");
        }

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

//Free the socket pointer
free(sockfd);

return 0;
}

Answer 1

几个问题:

在您的服务器中，您可以执行以下操作:

new_sock = malloc(1);

您只分配 1 个字节来保存 int 这空间不够。由于 newsock 指向 int，因此您应该为它分配足够的空间:

new_sock = malloc(sizeof(int));

同样在服务器中，您在读取来自客户端的消息后执行此操作:

    fd = open (PROCESSLIST, O_RDONLY);
    puts("file open has taken place");
    read(fd, buff, sizeof(*buff));
    puts("reading the file");
    write(sock, buff, 1);
    puts("writing to the buffer");
    puts("copied data from buffer to message");
    //Send the message back to client
    send(sock,message,strlen(message),0);

buff 是未初始化的 void *，因此尝试写入它会导致未定义的行为。 write 正在通过套接字从未初始化的 buff 发送单个字节，这可能不是您想要的。然后，您通过套接字从 message 发送数据，而不向其中放入任何内容。

这里您真正需要做的就是直接从文件读取到消息，然后发送。您首先需要清除 message 中的内存，以便在从文件读取后，它将以 NULL 终止。

因此您可以将上面的内容替换为:

    fd = open (PROCESSLIST, O_RDONLY);
    puts("file open has taken place");
    memset(message, 0, sizeof(message));
    read(fd, message, sizeof(message));
    puts("reading the file");
    //Send the message back to client
    send(sock,message,strlen(message),0);

在客户端中，您有 5 个线程尝试同时读取用户的消息。只有他们中的一个人能够做到。由于服务器忽略客户端发送的数据，因此最好让每个客户端线程发送一些虚拟数据而不提示用户，然后在从服务器获取消息后退出。