Hi Christian,

I attach the first attempt on SO_REUSEPORT. The patch is available
either at https://github.com/foxik/libmicrohttpd/commit/9ce9422742e10458f87275ea202a982e00c2b88c
or attached. (It is against the version with
MHD_DAEMON_OPTION_CURRENT_CONNECTIONS, but I can rebase it to current
SVN HEAD if you want.)

It seems that a reasonably multiplatform way of detecting SO_REUSEPORT is
  #ifdef SO_REPOSEPORT
which is used for example by Perl. For SO_EXCLUSIVEADDRUSE, the same
strategy seems to work too, according to Windows SDK headers and MinGW
WinAPI headers.

The current patch adds an option to allowing/disallowing address:port
reuse. One remark:
- currently both nonexisting SO_xxx and setsockopt failure are fatal and
  MHD_start_daemon fails. That may be too harsh -- maybe the
  MHD_OPTION_LISTENING_ADDRESS_REUSE should be only a hint.

  Nevertheless, as one can freely not use
  MHD_OPTION_LISTENING_ADDRESS_REUSE option, I chose the "fail on error"
  behaviour.

Thanks,
cheers,
Milan Straka

Original patch modified to get rid of some redundant USE_DEBUG
checks, fix indentation, and #ifndef SO_REUSEPORT on Linux,
we try be #defining it to 15 ourselves.

1 files changed, 14 insertions, 0 deletions

diff --git a/doc/libmicrohttpd.texi b/doc/libmicrohttpd.texi
index dcfbfc9d..91579c62 100644
--- a/doc/libmicrohttpd.texi
+++ b/doc/libmicrohttpd.texi
@@ -856,6 +856,20 @@ by the HTTPS daemon for key exchange.  This option must be followed by
 a @code{const char *} argument.  The argument would be a zero-terminated
 string with a PEM encoded PKCS3 DH parameters structure suitable
 for passing to @code{gnutls_dh_parms_import_pkcs3}.
+
+@item MHD_OPTION_LISTENING_ADDRESS_REUSE
+@cindex bind, restricting bind
+@cindex reusing listening address
+This option must be followed by a @code{unsigned int} argument.
+If this option is present and true (nonzero) parameter is given, allow reusing
+the address:port of the listening socket (using @code{SO_REUSEPORT} on most
+platforms, and @code{SO_REUSEADDR} on Windows).  If a false (zero) parameter is
+given, disallow reusing the the address:port of the listening socket (this
+usually requires no special action, but @code{SO_EXCLUSIVEADDRUSE} is needed on
+Windows).  If this option is not present, default behaviour is undefined
+(currently, @code{SO_REUSEADDR} is used on all platforms, which disallows
+address:port reusing with the exception of Windows).
+
 @end table
 @end deftp