Re: [libmicrohttpd] [GSoC Update] Week 2

[Evgeny Grin]

On 17.06.2017 11:36, Tim Rühsen wrote:
> On Samstag, 17. Juni 2017 13:53:06 CEST Didik Setiawan wrote:
>> On Tue, Jun 13, 2017 at 06:37:27PM +0200, Darshit Shah wrote:
>>>>   - http_server_port still hardcoded.
>>>
>>> This is important. The port should be a random number. Usually, passing 0
>>> in the port number makes the kernel choose an open one for you.
>>>
>>> Having a randomised port is important to ensure that multiple runs don't
>>> step on each other.
>>
>> I still don't know how to accomplish this. Maybe, it just my understanding
>> that when I pass 0 in MHD port number, the result is still 0.
>> Another approach, when I look into the old code, it generate port number by
>> calling wget_tcp_get_local_port(). But, I need to call wget_tcp_init() and
>> wget_tcp_listen() respectively in order to get proper result.
>> Conclusion, do I need to use existing wget_tcp_get_local_port() to get the
>> port, or maybe there is a function in MHD to do that?
> 
> All you need is the socket descriptor. How to call getsockname() + 
> getnameinfo() to retrieve the port number you see in libwget/net.c/
> wget_tcp_get_local_port().
> 
> If MHD doesn't have such a function, either try to get the socket descriptor 
> or extend MHD with a small function (similar code as in  
> wget_tcp_get_local_port).

There are several ways to implement it.
First one:
Initialise socket externally and start listen() on it. You can use any
bind and port detection function.
Pass socket FD to MHD_start_daemon() by MHD_OPTION_LISTEN_SOCKET.

Second one:
Use MHD_start_daemon() with "0" as port number then use
MHD_get_daemon_info() with MHD_DAEMON_INFO_LISTEN_FD to get listen
socket FD. Use any port detection.

Third one:
Implemented two day ago, works with MHD_VERSION >= 0x00095501 and on
platforms that support getsockname().
Use MHD_start_daemon() with "0" as port number then use
MHD_get_daemon_info() with MHD_DAEMON_INFO_BIND_PORT to get port number.


You can combine second and third methods:

-----------------------------------------------
  int port_num;

  if(0) {}
#if MHD_VERSION >= 0x00095501
  else if (MHD_NO !=
     MHD_is_feature_supported (MHD_FEATURE_AUTODETECT_BIND_PORT))
  {
    const union MHD_DaemonInfo *dinfo;
    dinfo = MHD_get_daemon_info (d, MHD_DAEMON_INFO_BIND_PORT);
    if (NULL == dinfo || 0 == dinfo->port)
    {
      /* Insert code to handle error. */
      return -1;
    }
    port_num = (int)dinfo->port;
  }
#endif /* MHD_VERSION >= 0x00095501 */
  else
  {
    const union MHD_DaemonInfo *dinfo;
    MHD_socket sock_fd;
    dinfo = MHD_get_daemon_info (d, MHD_OPTION_LISTEN_SOCKET);
    if (NULL == dinfo)
    {
      /* Insert code to handle error. */
      return -1;
    }
    sock_fd = dinfo->listen_fd;
    /* Insert code to use port detection on provided socket. */
  }
-----------------------------------------------

Note that socket type used by MHD functions is 'MHD_socket'.
MHD_socket is 'int' on POSIX platforms (Linux, *BSD, Unix, Darwin) and
'SOCKET' on Windows platform (excluding Cygwin, where MHD_socket is 'int').

-- 
Best Wishes,
Evgeny Grin

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