Rework AWS client's API to avoid stressing too much the stack.

When sending large payload over a socket with AWS.Client.Post we
ensure that no copy of the data is made on the stack to avoid a
stack overflow. This is especially important when a call is made
from a task where the stack may be limited.

Add corresponding regression test.

Fixes T527-014.

Author: TurboGit

regtests/0326_big_post/big_post.adb

@@ -0,0 +1,73 @@
+------------------------------------------------------------------------------
+--                              Ada Web Server                              --
+--                                                                          --
+--                       Copyright (C) 2020, AdaCore                        --
+--                                                                          --
+--  This is free software;  you can redistribute it  and/or modify it       --
+--  under terms of the  GNU General Public License as published  by the     --
+--  Free Software  Foundation;  either version 3,  or (at your option) any  --
+--  later version.  This software is distributed in the hope  that it will  --
+--  be useful, but WITHOUT 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  this  software;   see  file COPYING3.  If not, go    --
+--  to http://www.gnu.org/licenses for a complete copy of the license.      --
+------------------------------------------------------------------------------
+
+with Ada.Streams;
+with Ada.Text_IO;
+
+with AWS.Client;
+with AWS.Messages;
+with AWS.MIME;
+with AWS.Net.Log;
+with AWS.Parameters;
+with AWS.Response;
+with AWS.Server.Status;
+with AWS.Status;
+with AWS.Translator;
+with AWS.Utils;
+
+procedure Big_Post is
+
+   use Ada;
+   use Ada.Streams;
+   use AWS;
+
+   type String_Access is access String;
+
+   --------
+   -- CB --
+   --------
+
+   function CB (Request : Status.Data) return Response.Data is
+   begin
+      Text_IO.Put_Line
+        ("Length payload: " & Status.Content_Length (Request)'Img);
+      return Response.Build (MIME.Text_HTML, "ok");
+   end CB;
+
+   WS     : Server.HTTP;
+   M_Body : String_Access;
+   R      : Response.Data;
+
+begin
+   Server.Start (WS, "Big Post", CB'Unrestricted_Access, Port => 0);
+
+   Text_IO.Put_Line ("started");
+   Text_IO.Flush;
+
+   M_Body := new String'(1 .. 16_000_000 => 'a');
+
+   R := Client.Post
+          (Server.Status.Local_URL (WS) & "/big_post",
+           M_Body.all,
+           Content_Type => MIME.Text_HTML);
+
+   Text_IO.Put_Line (Response.Message_Body (R));
+
+   Server.Shutdown (WS);
+   Text_IO.Put_Line ("shutdown");
+end Big_Post;

regtests/0326_big_post/big_post.gpr

@@ -0,0 +1,23 @@
+------------------------------------------------------------------------------
+--                              Ada Web Server                              --
+--                                                                          --
+--                       Copyright (C) 2020, AdaCore                        --
+--                                                                          --
+--  This is free software;  you can redistribute it  and/or modify it       --
+--  under terms of the  GNU General Public License as published  by the     --
+--  Free Software  Foundation;  either version 3,  or (at your option) any  --
+--  later version.  This software is distributed in the hope  that it will  --
+--  be useful, but WITHOUT 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  this  software;   see  file COPYING3.  If not, go    --
+--  to http://www.gnu.org/licenses for a complete copy of the license.      --
+------------------------------------------------------------------------------
+
+with "aws";
+
+project Big_Post is
+   for Main use ("big_post.adb");
+end Big_Post;

regtests/0326_big_post/test.out

@@ -0,0 +1,4 @@
+started
+Length payload:  16000000
+ok
+shutdown

regtests/0326_big_post/test.py

@@ -0,0 +1,3 @@
+from test_support import *
+
+build_and_run('big_post');

src/core/aws-client.adb

@@ -678,17 +678,47 @@ package body AWS.Client is
       Attachments  : Attachment_List := Empty_Attachment_List;
       Headers      : Header_List     := Empty_Header_List) is
    begin
-      Internal_Post
-        (Connection,
-         Result,
-         Translator.To_Stream_Element_Array (Data),
-         URI,
-         SOAPAction   => No_Data,
-         Content_Type => (if Content_Type = No_Data
-                          then MIME.Application_Form_Data
-                          else Content_Type),
-         Attachments  => Attachments,
-         Headers      => Headers);
+      --  For message larger than 20kb the conversion to Stream_Element_Array
+      --  may create a stack overflow.
+
+      if Data'Length > 20 * 1024 then
+         declare
+            SEA : Utils.Stream_Element_Array_Access :=
+                    Translator.To_Stream_Element_Array (Data);
+         begin
+            Internal_Post
+              (Connection,
+               Result,
+               SEA.all,
+               URI,
+               SOAPAction   => No_Data,
+               Content_Type => (if Content_Type = No_Data
+                                then MIME.Application_Form_Data
+                                else Content_Type),
+               Attachments  => Attachments,
+               Headers      => Headers);
+
+            Utils.Unchecked_Free (SEA);
+
+         exception
+            when others =>
+               Utils.Unchecked_Free (SEA);
+               raise;
+         end;
+
+      else
+         Internal_Post
+           (Connection,
+            Result,
+            Translator.To_Stream_Element_Array (Data),
+            URI,
+            SOAPAction   => No_Data,
+            Content_Type => (if Content_Type = No_Data
+                             then MIME.Application_Form_Data
+                             else Content_Type),
+            Attachments  => Attachments,
+            Headers      => Headers);
+      end if;
    end Post;
 
    ---------

src/core/aws-net.adb

@@ -1,7 +1,7 @@
 ------------------------------------------------------------------------------
 --                              Ada Web Server                              --
 --                                                                          --
---                     Copyright (C) 2000-2019, AdaCore                     --
+--                     Copyright (C) 2000-2020, AdaCore                     --
 --                                                                          --
 --  This library is free software;  you can redistribute it and/or modify   --
 --  it under terms of the  GNU General Public License  as published by the  --
@@ -442,10 +442,12 @@ package body AWS.Net is
      (Socket : Socket_Type'Class; Data : Stream_Element_Array)
    is
       use Ada.Real_Time;
-      Save  : constant Boolean := Socket.C.Can_Wait;
-      First : Stream_Element_Offset := Data'First;
-      Last  : Stream_Element_Offset;
-      Stamp : Time;
+      Chunk_Size : constant := 100 * 1_024;
+      Save       : constant Boolean := Socket.C.Can_Wait;
+      First      : Stream_Element_Offset := Data'First;
+      Chunk_Last : Stream_Element_Offset := Data'Last;
+      Last       : Stream_Element_Offset;
+      Stamp      : Time;
    begin
       Socket.C.Can_Wait := True;
 
@@ -466,7 +468,10 @@ package body AWS.Net is
       end if;
 
       loop
-         Send (Socket, Data (First .. Data'Last), Last);
+         Chunk_Last :=
+           Stream_Element_Offset'Min (Data'Last, First + Chunk_Size - 1);
+
+         Send (Socket, Data (First .. Chunk_Last), Last);
 
          exit when Last = Data'Last;