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------------------------------------------------------------------------------

--                                                                          --

--                         GNAT COMPILER COMPONENTS                         --

--                                                                          --

--     G N A T . S O C K E T S . T H I N . S I G N A L L I N G _ F D S      --

--                                                                          --

--                                 B o d y                                  --

--                                                                          --

--                     Copyright (C) 2001-2008, AdaCore                     --

--                                                                          --

-- GNAT is free software;  you can  redistribute it  and/or modify it under --

-- terms of the  GNU General Public License as published  by the Free Soft- --

-- ware  Foundation;  either version 2,  or (at your option) any later ver- --

-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --

-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --

-- or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License --

-- for  more details.  You should have  received  a copy of the GNU General --

-- Public License  distributed with GNAT;  see file COPYING.  If not, write --

-- to  the  Free Software Foundation,  51  Franklin  Street,  Fifth  Floor, --

-- Boston, MA 02110-1301, USA.                                              --

--                                                                          --

-- As a special exception,  if other files  instantiate  generics from this --

-- unit, or you link  this unit with other files  to produce an executable, --

-- this  unit  does not  by itself cause  the resulting  executable  to  be --

-- covered  by the  GNU  General  Public  License.  This exception does not --

-- however invalidate  any other reasons why  the executable file  might be --

-- covered by the  GNU Public License.                                      --

--                                                                          --

-- GNAT was originally developed  by the GNAT team at  New York University. --

-- Extensive contributions were provided by Ada Core Technologies Inc.      --

--                                                                          --

------------------------------------------------------------------------------

--  Portable sockets-based implementation of GNAT.Sockets.Thin.Signalling_Fds

--  used for platforms that do not support UNIX pipes.

--  Note: this code used to be in GNAT.Sockets, but has been moved to a

--  platform-specific file. It is now used only for non-UNIX platforms.

separate (GNAT.Sockets.Thin)

package body Signalling_Fds is

   -----------

   -- Close --

   -----------

   procedure Close (Sig : C.int) is

      Res : C.int;

      pragma Unreferenced (Res);

      --  Res is assigned but never read, because we purposefully ignore

      --  any error returned by the C_Close system call, as per the spec

      --  of this procedure.

   begin

      Res := C_Close (Sig);

   end Close;

   ------------

   -- Create --

   ------------

   function Create (Fds : not null access Fd_Pair) return C.int is

      L_Sock, R_Sock, W_Sock : C.int := Failure;

      --  Listening socket, read socket and write socket

      Sin : aliased Sockaddr_In;

      Len : aliased C.int;

      --  Address of listening socket

      Res : C.int;

      pragma Warnings (Off, Res);

      --  Return status of system calls (usually ignored, hence warnings off)

   begin

      Fds.all := (Read_End | Write_End => Failure);

      --  We open two signalling sockets. One of them is used to send data

      --  to the other, which is included in a C_Select socket set. The

      --  communication is used to force the call to C_Select to complete,

      --  and the waiting task to resume its execution.

      loop

         --  Retry loop, in case the C_Connect below fails

         --  Create a listening socket

         L_Sock := C_Socket (SOSC.AF_INET, SOSC.SOCK_STREAM, 0);

         if L_Sock = Failure then

            goto Fail;

         end if;

         --  Bind the socket to an available port on localhost

         Set_Family (Sin.Sin_Family, Family_Inet);

         Sin.Sin_Addr.S_B1 := 127;

         Sin.Sin_Addr.S_B2 := 0;

         Sin.Sin_Addr.S_B3 := 0;

         Sin.Sin_Addr.S_B4 := 1;

         Sin.Sin_Port      := 0;

         Len := C.int (Lengths (Family_Inet));

         Res := C_Bind (L_Sock, Sin'Address, Len);

         if Res = Failure then

            goto Fail;

         end if;

         --  Get assigned port

         Res := C_Getsockname (L_Sock, Sin'Address, Len'Access);

         if Res = Failure then

            goto Fail;

         end if;

         --  Set socket to listen mode, with a backlog of 1 to guarantee that

         --  exactly one call to connect(2) succeeds.

         Res := C_Listen (L_Sock, 1);

         if Res = Failure then

            goto Fail;

         end if;

         --  Create read end (client) socket

         R_Sock := C_Socket (SOSC.AF_INET, SOSC.SOCK_STREAM, 0);

         if R_Sock = Failure then

            goto Fail;

         end if;

         --  Connect listening socket

         Res := C_Connect (R_Sock, Sin'Address, Len);

         exit when Res /= Failure;

         if Socket_Errno /= SOSC.EADDRINUSE then

            goto Fail;

         end if;

         --  In rare cases, the above C_Bind chooses a port that is still

         --  marked "in use", even though it has been closed (perhaps by some

         --  other process that has already exited). This causes the above

         --  C_Connect to fail with EADDRINUSE. In this case, we close the

         --  ports, and loop back to try again. This mysterious Windows

         --  behavior is documented. See, for example:

         --    http://msdn2.microsoft.com/en-us/library/ms737625.aspx

         --  In an experiment with 2000 calls, 21 required exactly one retry, 7

         --  required two, and none required three or more. Note that no delay

         --  is needed between retries; retrying C_Bind will typically produce

         --  a different port.

         pragma Assert (Res = Failure

                          and then

                        Socket_Errno = SOSC.EADDRINUSE);

         Res := C_Close (W_Sock);

         W_Sock := Failure;

         Res := C_Close (R_Sock);

         R_Sock := Failure;

      end loop;

      --  Since the call to connect(2) has succeeded and the backlog limit on

      --  the listening socket is 1, we know that there is now exactly one

      --  pending connection on L_Sock, which is the one from R_Sock.

      W_Sock := C_Accept (L_Sock, Sin'Address, Len'Access);

      if W_Sock = Failure then

         goto Fail;

      end if;

      --  Set TCP_NODELAY on W_Sock, since we always want to send the data out

      --  immediately.

      Set_Socket_Option

        (Socket => Socket_Type (W_Sock),

         Level  => IP_Protocol_For_TCP_Level,

         Option => (Name => No_Delay, Enabled => True));

      --  Close listening socket (ignore exit status)

      Res := C_Close (L_Sock);

      Fds.all := (Read_End => R_Sock, Write_End => W_Sock);

      return Thin_Common.Success;

   <<Fail>>

      declare

         Saved_Errno : constant Integer := Socket_Errno;

      begin

         if W_Sock /= Failure then

            Res := C_Close (W_Sock);

         end if;

         if R_Sock /= Failure then

            Res := C_Close (R_Sock);

         end if;

         if L_Sock /= Failure then

            Res := C_Close (L_Sock);

         end if;

         Set_Socket_Errno (Saved_Errno);

      end;

      return Failure;

   end Create;

   ----------

   -- Read --

   ----------

   function Read (Rsig : C.int) return C.int is

      Buf : aliased Character;

   begin

      return C_Recv (Rsig, Buf'Address, 1, SOSC.MSG_Forced_Flags);

   end Read;

   -----------

   -- Write --

   -----------

   function Write (Wsig : C.int) return C.int is

      Buf : aliased Character := ASCII.NUL;

   begin

      return C_Sendto

        (Wsig, Buf'Address, 1,

         Flags => SOSC.MSG_Forced_Flags,

         To    => System.Null_Address,

         Tolen => 0);

   end Write;

end Signalling_Fds;