1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT COMPILER COMPONENTS                         --
4--                                                                          --
5--     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      --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--                     Copyright (C) 2001-2018, AdaCore                     --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32--  Portable sockets-based implementation of GNAT.Sockets.Thin.Signalling_Fds
33--  used for platforms that do not support UNIX pipes.
34
35--  Note: this code used to be in GNAT.Sockets, but has been moved to a
36--  platform-specific file. It is now used only for non-UNIX platforms.
37
38separate (GNAT.Sockets.Thin)
39package body Signalling_Fds is
40
41   -----------
42   -- Close --
43   -----------
44
45   procedure Close (Sig : C.int) is
46      Res : C.int;
47      pragma Unreferenced (Res);
48      --  Res is assigned but never read, because we purposefully ignore
49      --  any error returned by the C_Close system call, as per the spec
50      --  of this procedure.
51   begin
52      Res := C_Close (Sig);
53   end Close;
54
55   ------------
56   -- Create --
57   ------------
58
59   function Create (Fds : not null access Fd_Pair) return C.int is
60      L_Sock, R_Sock, W_Sock : C.int := Failure;
61      --  Listening socket, read socket and write socket
62
63      Sin : aliased Sockaddr_In;
64      Len : aliased C.int;
65      --  Address of listening socket
66
67      Res : C.int;
68      pragma Warnings (Off, Res);
69      --  Return status of system calls (usually ignored, hence warnings off)
70
71   begin
72      Fds.all := (Read_End | Write_End => Failure);
73
74      --  We open two signalling sockets. One of them is used to send data
75      --  to the other, which is included in a C_Select socket set. The
76      --  communication is used to force the call to C_Select to complete,
77      --  and the waiting task to resume its execution.
78
79      loop
80         --  Retry loop, in case the C_Connect below fails
81
82         --  Create a listening socket
83
84         L_Sock := C_Socket (SOSC.AF_INET, SOSC.SOCK_STREAM, 0);
85
86         if L_Sock = Failure then
87            goto Fail;
88         end if;
89
90         --  Bind the socket to an available port on localhost
91
92         Set_Family (Sin.Sin_Family, Family_Inet);
93         Sin.Sin_Addr.S_B1 := 127;
94         Sin.Sin_Addr.S_B2 := 0;
95         Sin.Sin_Addr.S_B3 := 0;
96         Sin.Sin_Addr.S_B4 := 1;
97         Sin.Sin_Port      := 0;
98
99         Len := C.int (Lengths (Family_Inet));
100         Res := C_Bind (L_Sock, Sin'Address, Len);
101
102         if Res = Failure then
103            goto Fail;
104         end if;
105
106         --  Get assigned port
107
108         Res := C_Getsockname (L_Sock, Sin'Address, Len'Access);
109         if Res = Failure then
110            goto Fail;
111         end if;
112
113         --  Set socket to listen mode, with a backlog of 1 to guarantee that
114         --  exactly one call to connect(2) succeeds.
115
116         Res := C_Listen (L_Sock, 1);
117
118         if Res = Failure then
119            goto Fail;
120         end if;
121
122         --  Create read end (client) socket
123
124         R_Sock := C_Socket (SOSC.AF_INET, SOSC.SOCK_STREAM, 0);
125
126         if R_Sock = Failure then
127            goto Fail;
128         end if;
129
130         --  Connect listening socket
131
132         Res := C_Connect (R_Sock, Sin'Address, Len);
133
134         exit when Res /= Failure;
135
136         if Socket_Errno /= SOSC.EADDRINUSE then
137            goto Fail;
138         end if;
139
140         --  In rare cases, the above C_Bind chooses a port that is still
141         --  marked "in use", even though it has been closed (perhaps by some
142         --  other process that has already exited). This causes the above
143         --  C_Connect to fail with EADDRINUSE. In this case, we close the
144         --  ports, and loop back to try again. This mysterious Windows
145         --  behavior is documented. See, for example:
146         --    http://msdn2.microsoft.com/en-us/library/ms737625.aspx
147         --  In an experiment with 2000 calls, 21 required exactly one retry, 7
148         --  required two, and none required three or more. Note that no delay
149         --  is needed between retries; retrying C_Bind will typically produce
150         --  a different port.
151
152         pragma Assert (Res = Failure
153                          and then
154                        Socket_Errno = SOSC.EADDRINUSE);
155         Res := C_Close (W_Sock);
156         W_Sock := Failure;
157         Res := C_Close (R_Sock);
158         R_Sock := Failure;
159      end loop;
160
161      --  Since the call to connect(2) has succeeded and the backlog limit on
162      --  the listening socket is 1, we know that there is now exactly one
163      --  pending connection on L_Sock, which is the one from R_Sock.
164
165      W_Sock := C_Accept (L_Sock, Sin'Address, Len'Access);
166
167      if W_Sock = Failure then
168         goto Fail;
169      end if;
170
171      --  Set TCP_NODELAY on W_Sock, since we always want to send the data out
172      --  immediately.
173
174      Set_Socket_Option
175        (Socket => Socket_Type (W_Sock),
176         Level  => IP_Protocol_For_TCP_Level,
177         Option => (Name => No_Delay, Enabled => True));
178
179      --  Close listening socket (ignore exit status)
180
181      Res := C_Close (L_Sock);
182
183      Fds.all := (Read_End => R_Sock, Write_End => W_Sock);
184
185      return Thin_Common.Success;
186
187   <<Fail>>
188      declare
189         Saved_Errno : constant Integer := Socket_Errno;
190
191      begin
192         if W_Sock /= Failure then
193            Res := C_Close (W_Sock);
194         end if;
195
196         if R_Sock /= Failure then
197            Res := C_Close (R_Sock);
198         end if;
199
200         if L_Sock /= Failure then
201            Res := C_Close (L_Sock);
202         end if;
203
204         Set_Socket_Errno (Saved_Errno);
205      end;
206
207      return Failure;
208   end Create;
209
210   ----------
211   -- Read --
212   ----------
213
214   function Read (Rsig : C.int) return C.int is
215      Buf : aliased Character;
216   begin
217      return C_Recv (Rsig, Buf'Address, 1, SOSC.MSG_Forced_Flags);
218   end Read;
219
220   -----------
221   -- Write --
222   -----------
223
224   function Write (Wsig : C.int) return C.int is
225      Buf : aliased Character := ASCII.NUL;
226   begin
227      return C_Sendto
228        (Wsig, Buf'Address, 1,
229         Flags => SOSC.MSG_Forced_Flags,
230         To    => System.Null_Address,
231         Tolen => 0);
232   end Write;
233
234end Signalling_Fds;
235