Talking to SMTP Server in C with send()

Question

I'm programming an interactive SMTP Client, which can talk to an SMTP Server though the terminal. So far I've established a connection (server response 220 after first recv()), and then try to send a HELO to the Server. The send function gives me a return value of 15, so that should be working. But then I try to read the response (which should be 250 OK), but the program blocks and returns nothing. I'm using fake SMTP as a testing Server.

Here is my code so far:

char IPADDRESS []= "127.0.0.1";

int initConnect(){

   int sock = socket(AF_INET, SOCK_STREAM, 0);

   setsockopt(sock, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT,NULL, 0);

   struct sockaddr_in serv_addr;
   memset(&serv_addr, '0', sizeof(serv_addr));
   serv_addr.sin_port = htons(25);
   serv_addr.sin_family = AF_INET;

   if(inet_pton(AF_INET, IPADDRESS, &serv_addr.sin_addr) > 0){

      connect(sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr));

   }else{

      return -1;

   }

   return sock;

 }


 int main(void){

   char buffer[1024];

   memset(buffer, 0, sizeof(buffer));
   int FLAGS = 0;

   int fd;
   fd = initConnect();

   if(fd == -1){

      printf("Error occured while connecting to the Server");
      exit(1);

   } else {

     printf("  ->   Connected\n");

   }

   // get response from Server after connection
   int recBytes =   recv(fd, buffer, sizeof(buffer), FLAGS);
   printf("Server: %s", buffer);

   // send HELO cmd to Sever (if < 0 error)
   int ret = send(fd, "HELO 127.0.0.1\n", strlen("HELO 127.0.0.1\n"), FLAGS);
   printf("\nSend bytes: %i\n", ret);

   // get response from Server after HELO (program blocks here)
   memset(buffer, 0, sizeof(buffer));
   recBytes = recv(fd, buffer, sizeof(buffer), FLAGS);
   printf("\nServer: %s", buffer);
}

Answer 1

The SMTP RFC says:

Lines consist of zero or more data characters terminated by the sequence ASCII character "CR" (hex value 0D) followed immediately by ASCII character "LF" (hex value 0A).

Your code only sends <LF> (\n) so needs to be changed to \r\n.