sendfile

server.c

/* receive e-mail */
void receive_mail(char *filename, int sock_fd)
{
   /* file descriptor for destination file */
   int destination_fd;
   
   /* byte offset used by sendfile */
   off_t offset = 0;
   
   size_t total_bytes_sent = 0; 
   
   struct stat stat_buf;
   
   /* open destination file */
   destination_fd = open(filename, O_WRONLY | O_CREAT);
   
      /* checking for "open" errors */
      if (destination_fd < 0)
      { exit(EXIT_FAILURE); }
      
   fstat(destination_fd, &stat_buf);   
   
   (void)fprintf(stdout, "File size: %jd\n", (intmax_t)stat_buf.st_size);
   
   /* receive file */
   total_bytes_sent = do_recvfile(1, sock_fd, offset, /* HERE I NEED THE FILE SIZE: ON SERVER-SIDE IT IS UNKNOWN */);
   
   (void)fprintf(stdout, "Total bytes sent: %d\n", total_bytes_sent);
   
   close(destination_fd);
}

/* receive file */
ssize_t do_recvfile(int output_fd, int sock_fd, off_t offset, size_t count)
{
   ssize_t bytes;
   
   ssize_t bytes_sent;
   
   ssize_t bytes_in_pipe;
   
   size_t total_bytes_sent = 0;
   
   /* pipe */
   int pipefd[2];   
           
      /* setup the pipe */
      if (pipe(pipefd) < 0)
      {
         err_num = errno;
      
         (void)fprintf(stderr, "\"pipe\" error:%s\n", strerror(err_num));
         
         exit(EXIT_FAILURE);
      } 
   
      /* splice the data from "sock_fd" into the pipe */
      while (total_bytes_sent < count)
      {
            if ((bytes_sent = splice(sock_fd, NULL, pipefd[1], NULL,
                MIN(count - total_bytes_sent, 16384), 
                SPLICE_F_MORE | SPLICE_F_MOVE)) <= 0) {
                  if (errno == EINTR || errno == EAGAIN)
                  { continue; }
               
               err_num = errno;
                  
               (void)fprintf(stderr, "\"splice\" error (bytes_sent): %s\n", strerror(err_num));
               
               return (-1);
            }
            
         bytes_in_pipe = bytes_sent;
            
            while (bytes_in_pipe > 0)
            {
                  if ((bytes = splice(pipefd[0], NULL, output_fd, &offset, bytes_in_pipe, SPLICE_F_MORE | SPLICE_F_MOVE)) <= 0)
                  {
                        if (errno == EINTR || errno == EAGAIN)
                        { continue; }
                        
                     err_num = errno;   
                     
                     (void)fprintf(stderr, "\"splice\" error (bytes): %s\n", strerror(err_num));
                     
                     return (-1);
                  }
                  
               bytes_in_pipe -= bytes;
            }
            
         total_bytes_sent += bytes_sent;
      }

   return (total_bytes_sent);
}