title: TCP Client-Server "bad address" error (in C)
body: <p>Although it seems to be correctly implemented, <strong>it keeps on returning me <em>ERROR</em> when I establish a connection using the loopback address</strong>(127.0.0.1).</p>
  
  <p>In addition to a simple TCP Client/Server connection, I have added an additional case:</p>
  
  <p>If the client tries to send data but <strong>finds the connection closed</strong>, it is closed too. I perform it by <strong>checking if received data is equal to 0 (recv)</strong>.</p>
  
  <p><strong>Given error</strong>:</p>
  
  <pre><code>CLIENT:
  Welcome to the Client mode
  Please, enter the Server's IP Address and Port (eg. 192.128.192.0 1320) 
  127.0.0.1 2700
  Connected to the server. Now you can send messages
  Please, enter a message. Enter "FINISH" if you want to finish the connection
  ECHO 
  client: connection closed -&gt;: Success
   (1 bytes)Closing the connection 
  
  SERVER:
  Hello and welcome to the Server mode
  Please, enter the Server's Port (eg. 1320) 
  2700
  Server socket successfully configured
  Server listening [Clients allowed: 5]
  server: accept error: Bad address
  </code></pre>
  
  <p><strong>Client</strong> implementation:</p>
  
  <pre><code>#include &lt;sys/types.h&gt;
  #include &lt;sys/socket.h&gt;
  #include &lt;netinet/in.h&gt;
  #include &lt;arpa/inet.h&gt;
  #include &lt;netdb.h&gt;
  #include &lt;stdio.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;string.h&gt;
  #include &lt;unistd.h&gt;
  
  #include &lt;netinet/in.h&gt;
  #include &lt;netinet/ip.h&gt;
  
  /**
  
   struct sockaddr{
       uint8_t sa_len; // struct length
       sa_family_t sa_family; //protocol family: AF_XXX
       char sa_data[8]; //socket addr
   }
  
   */
  
  //void notConnected();
  int main(){
  
      struct sockaddr_in  serv_addr;  //port + ip_addr
      int                 my_socket, tcp_port;
      char                serv_host_addr[30];
  
      char                buffer[1024], inbuff[1024];
      int                 io_buffer;
  
      printf("Welcome to the Client mode\n");
  
      //CONFIGURING THE CONNECTION
      my_socket = socket(AF_INET, SOCK_STREAM, 0);//(2)
      if(my_socket &lt; 0){
          perror("client: socket() error -&gt;");
          exit(EXIT_FAILURE);
      }
  
      bzero(&amp;serv_addr, sizeof(serv_addr));//(4)
      printf("Please, enter the Server's IP Address and Port (eg. 192.128.192.0 1320) \n");
      scanf("%s %d", serv_host_addr, &amp;tcp_port);//(1)
  
  
      serv_addr.sin_family = AF_INET ;
      serv_addr.sin_port = htons(tcp_port);
      if(inet_pton(AF_INET,serv_host_addr,&amp;serv_addr.sin_addr) &lt; 1){
          perror("client: inet_pton() error -&gt;");
          exit(EXIT_FAILURE);
      }
  
      if((connect(my_socket, (struct sockaddr *) &amp;serv_addr, sizeof(serv_addr) )) &lt; 0)//(5)
      {
          perror("client: connect() error -&gt;");
          exit(EXIT_FAILURE);
      }
  
  
      //ONCE CONNECTED, START THE SENDING/RECEIVING
      printf("Connected to the server. Now you can send messages\n");
      bzero(&amp;buffer, sizeof(buffer));
  
      while(strcmp(buffer, "OK\n") != 0){
  
          printf("Please, enter a message. Enter \"FINISH\" if you want to finish the connection\n");//(3)
          bzero(&amp;buffer, sizeof(buffer));
          fgets(buffer, sizeof(buffer), stdin);
  
          io_buffer = send(my_socket, buffer, strlen(buffer),0);//(6)
          if(io_buffer &lt; 0){
              perror("client: send() error -&gt;");
              exit(EXIT_FAILURE);
          }
          printf("ECHO %s (%d bytes)", buffer, io_buffer);
  
  
          //RECEIVE AND CHECK IF CONNECTION HAS BEEN CLOSED
          io_buffer = recv(my_socket, buffer, sizeof(buffer),0);
          if(io_buffer &lt; 0){
              perror("client: recv() error -&gt;");
              exit(EXIT_FAILURE);
          }
          else if(io_buffer == 0){    //THIS IS SERVER IS CLOSED
              perror("client: connection closed -&gt;");
              break;
          }
          printf("ECHO %s (%d bytes)", buffer, io_buffer);
  
      }
  
      printf("Closing the connection \n");
      for(int i=0; i &lt; 5; i++){
          printf(". ");
          usleep(500000);
      }
      close(my_socket);
  }
  </code></pre>
  
  <p><strong>Server</strong> implementation:</p>
  
  <pre><code>#include &lt;sys/types.h&gt;
  #include &lt;sys/socket.h&gt;
  #include &lt;netinet/in.h&gt;
  #include &lt;arpa/inet.h&gt;
  #include &lt;netdb.h&gt;
  #include &lt;stdio.h&gt;
  #include &lt;stdlib.h&gt;
  #include &lt;string.h&gt;
  #include &lt;unistd.h&gt;
  
  #define LISTENQ 5
  
  int main()
  {
      struct sockaddr_in  cli_addr, serv_addr;
      char                buffer[1024];
      int                 serv_socket, cli_socket, clilen, io_buffer;
      int                 tcp_port;
  
  printf("Hello and welcome to the Server mode\n");
  
  //  ASKING FOR PORT NUMBER
      if((serv_socket = socket(AF_INET, SOCK_STREAM, 0)) &lt; 0){
          perror("server: can't open stream socket");
          exit(EXIT_FAILURE);
      }
  
  printf("Please, enter the Server's Port (eg. 1320) \n");
      scanf("%d", &amp;tcp_port);
  
  //  CONFIGURING THE CONNECTION
      serv_addr.sin_family        = AF_INET;
      serv_addr.sin_port          = htons(tcp_port);
      serv_addr.sin_addr.s_addr   = htonl(INADDR_ANY);
  
  //  ASSIGNING A NAME TO THE SOCKET
      if(bind(serv_socket,(struct sockaddr *) &amp;serv_addr,sizeof(serv_addr)) &lt; 0){
          perror("server: can't assign a name to the socket");
          exit(EXIT_FAILURE);
      }
  printf("Server socket successfully configured\n");
  
  printf("Server listening [Clients allowed: %d]\n", LISTENQ);
      if(listen(serv_socket, LISTENQ) &lt; 0)
      {
          perror("server: fail to listen network");
          exit(EXIT_FAILURE);
      }
  
  //  READ &amp; WRITE STREAM
      while(1){
          //returns a file descriptor for the client
          cli_socket = accept(serv_socket,(struct sockaddr *) &amp;cli_addr,(socklen_t *) sizeof(cli_addr));
  
          if(cli_socket &lt; 0){
              perror("server: accept error");
              exit(EXIT_FAILURE);
          }
          printf("Server successfully connected to Client\n");
  
          while(1)
          {
  
              if ((io_buffer=recv(cli_socket,buffer,sizeof(buffer),0))&lt;0){
                  perror("ERROR: recv");
                  exit(EXIT_FAILURE);
              }
              printf("\"%s\" received from client", buffer);
  
              if(strcmp(buffer, "FINISH") == 0)
              {
                  break;
              }
  
              if ((io_buffer=send(cli_socket,buffer,strlen(buffer),0))!=strlen(buffer)){
                  perror("ERROR: send");
                  exit(EXIT_FAILURE);
              }
  
              bzero(buffer, sizeof(buffer));
          }
  
          strcpy(buffer, "OK");
          if ((io_buffer=send(cli_socket, buffer, strlen(buffer), 0)) != strlen(buffer)){
              perror("ERROR: send");
              exit(EXIT_FAILURE);
          }
          printf("\"OK\" message sent to the Client.\n");
          printf("Closing the connection \n");
          for(int i=0; i &lt; 5; i++)
          {
              printf(". ");
              usleep(500000);
          }
          close(cli_socket);
      }
  }
  </code></pre>