A.1.6   Programmation réseau

• Montrer les appels systèmes avec :

  $ strace nc -l -p 4000
  ...
  socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
  setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
  bind(3, {sin_family=AF_INET, sin_port=htons(4000),
           sin_addr=inet_addr("0.0.0.0")}}, 16) = 0
  listen(3, 1)                            = 0
  rt_sigaction(SIGALRM, {SIG_IGN}, {SIG_DFL}, 8) = 0
  alarm(0)                                = 0
  accept(3, 
  

• Montrer le fonctionnement d'un serveur TCP :

  # strace -f /usr/sbin/ftpd -s -p 2121
  # strace ftp localhost 2121
  

• Montrer le fonctionnement d'un serveur UDP :

  # strace -f nc -u -l -p 4000
  ...
  socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 3
  setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
  bind(3, {sin_family=AF_INET, sin_port=htons(4000), sin_addr=inet_addr("0.0.0.0")}}, 16) = 0
  rt_sigaction(SIGALRM, {SIG_IGN}, {SIG_DFL}, 8) = 0
  alarm(0)                                = 0
  recvfrom(3, ...
              ... {sin_family=AF_INET, sin_port=htons(4000),
                   sin_addr=inet_addr("127.0.0.1")}}, [16]) = 0
  select(16, [0 3], NULL, NULL, NULL)     = 1 (in [3])
  read(3, "\n", 8192)                     = 1
  write(1, "\n", 1)                       = 1
  ...
  # strace nc -u localhost 4000
  socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP) = 3
  setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
  rt_sigaction(SIGALRM, {SIG_IGN}, {SIG_DFL}, 8) = 0
  alarm(0)                                = 0
  connect(3, {sin_family=AF_INET, sin_port=htons(4000),
              sin_addr=inet_addr("127.0.0.1")}}, 16) = 0
  rt_sigaction(SIGALRM, {SIG_IGN}, {SIG_IGN}, 8) = 0
  alarm(0)                                = 0
  select(16, [0 3], NULL, NULL, NULL)     = 1 (in [0])
  read(0, "\n", 8192)                     = 1
  write(3, "\n", 1)                       = 1 
  ...
  

• Exemple de fichier /etc/inetd.conf.

  #
  # <service_name> <sock_type> <proto> <flags> <user> <server_path> <args>
  #
  #:INTERNAL: Internal services
  #
  echo     stream tcp nowait root            internal
  echo     dgram  udp wait   root            internal
  chargen  stream tcp nowait root            internal
  chargen  dgram  udp wait   root            internal
  discard  stream tcp nowait root            internal
  discard  dgram  udp wait   root            internal
  daytime  stream tcp nowait root            internal
  daytime  dgram  udp wait   root            internal
  time     stream tcp nowait root            internal
  time     dgram  udp wait   root            internal
  
  #:STANDARD: These are standard services.
  #
  telnet   stream tcp nowait telnetd.telnetd /usr/sbin/tcpd /usr/sbin/in.telnetd
  ftp      stream tcp nowait root            /usr/sbin/tcpd /usr/sbin/wu-ftpd -l
  telnet   stream tcp nowait telnetd.telnetd /usr/sbin/tcpd /usr/sbin/in.telnetd
  
  #:BSD: Shell, login, exec and talk are BSD protocols.
  #
  shell    stream tcp nowait root           /usr/sbin/tcpd  /usr/sbin/in.rshd
  login    stream tcp nowait root           /usr/sbin/tcpd  /usr/sbin/in.rlogind
  exec     stream tcp nowait root           /usr/sbin/tcpd  /usr/sbin/in.rexecd
  talk     dgram  udp wait   root.tty       /usr/sbin/tcpd  /usr/sbin/kotalkd
  ntalk    dgram  udp wait   root.tty       /usr/sbin/tcpd  /usr/sbin/ktalkd