test

client.cpp

@@ -1,4 +1,180 @@
-int main (int argc, char* argv[])
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+///////////////////////////////////////////////////////////////////////////////
+
+#define BUF 1024
+#define PORT 6543
+
+///////////////////////////////////////////////////////////////////////////////
+
+int main(int argc, char **argv)
 {
+   int create_socket;
+   char buffer[BUF];
+   struct sockaddr_in address;
+   int size;
+   int isQuit;
+
+   ////////////////////////////////////////////////////////////////////////////
+   // CREATE A SOCKET
+   // https://man7.org/linux/man-pages/man2/socket.2.html
+   // https://man7.org/linux/man-pages/man7/ip.7.html
+   // https://man7.org/linux/man-pages/man7/tcp.7.html
+   // IPv4, TCP (connection oriented), IP (same as server)
+   if ((create_socket = socket(AF_INET, SOCK_STREAM, 0)) == -1)
+   {
+      perror("Socket error");
+      return EXIT_FAILURE;
+   }
+
+   ////////////////////////////////////////////////////////////////////////////
+   // INIT ADDRESS
+   // Attention: network byte order => big endian
+   memset(&address, 0, sizeof(address)); // init storage with 0
+   address.sin_family = AF_INET;         // IPv4
+   // https://man7.org/linux/man-pages/man3/htons.3.html
+   address.sin_port = htons(PORT);
+   // https://man7.org/linux/man-pages/man3/inet_aton.3.html
+   if (argc < 2)
+   {
+      inet_aton("127.0.0.1", &address.sin_addr);
+   }
+   else
+   {
+      inet_aton(argv[1], &address.sin_addr);
+   }
+
+   ////////////////////////////////////////////////////////////////////////////
+   // CREATE A CONNECTION
+   // https://man7.org/linux/man-pages/man2/connect.2.html
+   if (connect(create_socket,
+               (struct sockaddr *)&address,
+               sizeof(address)) == -1)
+   {
+      // https://man7.org/linux/man-pages/man3/perror.3.html
+      perror("Connect error - no server available");
+      return EXIT_FAILURE;
+   }
+
+   // ignore return value of printf
+   printf("Connection with server (%s) established\n",
+          inet_ntoa(address.sin_addr));
+
+   ////////////////////////////////////////////////////////////////////////////
+   // RECEIVE DATA
+   // https://man7.org/linux/man-pages/man2/recv.2.html
+   size = recv(create_socket, buffer, BUF - 1, 0);
+   if (size == -1)
+   {
+      perror("recv error");
+   }
+   else if (size == 0)
+   {
+      printf("Server closed remote socket\n"); // ignore error
+   }
+   else
+   {
+      buffer[size] = '\0';
+      printf("%s", buffer); // ignore error
+   }
+
+   do
+   {
+      printf(">> ");
+      if (fgets(buffer, BUF - 1, stdin) != NULL)
+      {
+         int size = strlen(buffer);
+         // remove new-line signs from string at the end
+         if (buffer[size - 2] == '\r' && buffer[size - 1] == '\n')
+         {
+            size -= 2;
+            buffer[size] = 0;
+         }
+         else if (buffer[size - 1] == '\n')
+         {
+            --size;
+            buffer[size] = 0;
+         }
+         isQuit = strcmp(buffer, "quit") == 0;
+
+         //////////////////////////////////////////////////////////////////////
+         // SEND DATA
+         // https://man7.org/linux/man-pages/man2/send.2.html
+         // send will fail if connection is closed, but does not set
+         // the error of send, but still the count of bytes sent
+         if ((send(create_socket, buffer, size + 1, 0)) == -1) 
+         {
+            // in case the server is gone offline we will still not enter
+            // this part of code: see docs: https://linux.die.net/man/3/send
+            // >> Successful completion of a call to send() does not guarantee 
+            // >> delivery of the message. A return value of -1 indicates only 
+            // >> locally-detected errors.
+            // ... but
+            // to check the connection before send is sense-less because
+            // after checking the communication can fail (so we would need
+            // to have 1 atomic operation to check...)
+            perror("send error");
+            break;
+         }
+
+         //////////////////////////////////////////////////////////////////////
+         // RECEIVE FEEDBACK
+         // consider: reconnect handling might be appropriate in somes cases
+         //           How can we determine that the command sent was received 
+         //           or not? 
+         //           - Resend, might change state too often. 
+         //           - Else a command might have been lost.
          //
+         // solution 1: adding meta-data (unique command id) and check on the
+         //             server if already processed.
+         // solution 2: add an infrastructure component for messaging (broker)
+         //
+         size = recv(create_socket, buffer, BUF - 1, 0);
+         if (size == -1)
+         {
+            perror("recv error");
+            break;
+         }
+         else if (size == 0)
+         {
+            printf("Server closed remote socket\n"); // ignore error
+            break;
+         }
+         else
+         {
+            buffer[size] = '\0';
+            printf("<< %s\n", buffer); // ignore error
+            if (strcmp("OK", buffer) != 0)
+            {
+               fprintf(stderr, "<< Server error occured, abort\n");
+               break;
+            }
+         }
+      }
+   } while (!isQuit);
+
+   ////////////////////////////////////////////////////////////////////////////
+   // CLOSES THE DESCRIPTOR
+   if (create_socket != -1)
+   {
+      if (shutdown(create_socket, SHUT_RDWR) == -1)
+      {
+         // invalid in case the server is gone already
+         perror("shutdown create_socket"); 
+      }
+      if (close(create_socket) == -1)
+      {
+         perror("close create_socket");
+      }
+      create_socket = -1;
+   }
+
+   return EXIT_SUCCESS;
 }