read_write.c

#include "common.h"

/* Read from the keyboard and write to the server
   Read from the server and write to the keyboard

   we use select() to multiplex
*/
void read_write(SSL *ssl,int sock)
{
    int width;
    int r,c2sl=0,c2s_offset=0;
    int read_blocked_on_write=0,write_blocked_on_read=0,read_blocked=0;
    fd_set readfds,writefds;
    int shutdown_wait=0;
    char c2s[BUFSIZZ],s2c[BUFSIZZ];
    int ofcmode;
    
    /*First we make the socket nonblocking*/
    ofcmode=fcntl(sock,F_GETFL,0);
    ofcmode|=O_NDELAY;
    if(fcntl(sock,F_SETFL,ofcmode))
      err_exit("Couldn't make socket nonblocking");
    

    width=sock+1;
    
    while(1){
      FD_ZERO(&readfds);
      FD_ZERO(&writefds);

      FD_SET(sock,&readfds);

      /* If we're waiting for a read on the socket don't
         try to write to the server */
      if(!write_blocked_on_read){
        /* If we have data in the write queue don't try to
           read from stdin */
        if(c2sl || read_blocked_on_write)
          FD_SET(sock,&writefds);
        else
          FD_SET(fileno(stdin),&readfds);
      }
      
      r=select(width,&readfds,&writefds,0,0);
      if(r==0)
        continue;

      /* Now check if there's data to read */
      if((FD_ISSET(sock,&readfds) && !write_blocked_on_read) ||
        (read_blocked_on_write && FD_ISSET(sock,&writefds))){
        do {
          read_blocked_on_write=0;
          read_blocked=0;
          
          r=SSL_read(ssl,s2c,BUFSIZZ);
          
          switch(SSL_get_error(ssl,r)){
            case SSL_ERROR_NONE:
              /* Note: this call could block, which blocks the
                 entire application. It's arguable this is the
                 right behavior since this is essentially a terminal
                 client. However, in some other applications you
                 would have to prevent this condition */
              fwrite(s2c,1,r,stdout);
              break;
            case SSL_ERROR_ZERO_RETURN:
              /* End of data */
              if(!shutdown_wait)
                SSL_shutdown(ssl);
              goto end;
              break;
            case SSL_ERROR_WANT_READ:
              read_blocked=1;
              break;
              
              /* We get a WANT_WRITE if we're
                 trying to rehandshake and we block on
                 a write during that rehandshake.

                 We need to wait on the socket to be 
                 writeable but reinitiate the read
                 when it is */
            case SSL_ERROR_WANT_WRITE:
              read_blocked_on_write=1;
              break;
            default:
              berr_exit("SSL read problem");
          }

          /* We need a check for read_blocked here because
             SSL_pending() doesn't work properly during the
             handshake. This check prevents a busy-wait
             loop around SSL_read() */
        } while (SSL_pending(ssl) && !read_blocked);
      }
      
      /* Check for input on the console*/
      if(FD_ISSET(fileno(stdin),&readfds)){
        c2sl=read(fileno(stdin),c2s,BUFSIZZ);
        if(c2sl==0){
          shutdown_wait=1;
          if(SSL_shutdown(ssl))
            return;
        }
        c2s_offset=0;
      }

      /* If the socket is writeable... */
      if((FD_ISSET(sock,&writefds) && c2sl) ||
        (write_blocked_on_read && FD_ISSET(sock,&readfds))) {
        write_blocked_on_read=0;

        /* Try to write */
        r=SSL_write(ssl,c2s+c2s_offset,c2sl);
          
        switch(SSL_get_error(ssl,r)){
          /* We wrote something*/
          case SSL_ERROR_NONE:
            c2sl-=r;
            c2s_offset+=r;
            break;
              
            /* We would have blocked */
          case SSL_ERROR_WANT_WRITE:
            break;

            /* We get a WANT_READ if we're
               trying to rehandshake and we block on
               write during the current connection.
               
               We need to wait on the socket to be readable
               but reinitiate our write when it is */
          case SSL_ERROR_WANT_READ:
            write_blocked_on_read=1;
            break;
              
              /* Some other error */
          default:	      
            berr_exit("SSL write problem");
        }
      }
    }
      
  end:
    SSL_free(ssl);
    close(sock);
    return;
  }