Index: lcl/interfaces/gtk2/gtk2callback.inc
===================================================================
--- lcl/interfaces/gtk2/gtk2callback.inc	(wersja 35868)
+++ lcl/interfaces/gtk2/gtk2callback.inc	(kopia robocza)
@@ -3362,6 +3362,9 @@
             if BufLength>0 then begin
               GetMem(Buffer,BufLength);
               MemStream.Read(Buffer^,BufLength);
+              // LCL attaches trailing zero - remove it.
+              if PByte(Buffer)[BufLength-1] = 0 then
+                Dec(BufLength);
               {SetLength(s,MemStream.Size);
               MemStream.Position:=0;
               MemStream.Read(s[1],MemStream.Size);

From 3ba3d9b44660621e69a6da7d391a37c8db666445 Mon Sep 17 00:00:00 2001
From: Basile Burg <basile.b@gmx.com>
Date: Thu, 17 Nov 2016 00:32:38 +0100
Subject: [PATCH] fix issues 21453 and 30071

Under gtk2, the clipboard content doesn't need a null terminator because
it's added by GTK automatically
---
 lcl/interfaces/gtk2/gtk2callback.inc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lcl/interfaces/gtk2/gtk2callback.inc b/lcl/interfaces/gtk2/gtk2callback.inc
index 51fd155..4ee068b 100644
--- a/lcl/interfaces/gtk2/gtk2callback.inc
+++ b/lcl/interfaces/gtk2/gtk2callback.inc
@@ -3678,6 +3678,10 @@ begin
           {$IFDEF DEBUG_CLIPBOARD}
           DebugLn('[ClipboardSelectionRequestHandler] Len=',dbgs(BufLength));
           {$ENDIF}
+          // workaround for issues 21453 and 30071.
+          // gtk_selection_data_set auto adds the required null term.
+          if PChar(Buffer + BufLength - 1)^ = #0 then
+            dec(BufLength);
           gtk_selection_data_set(SelectionData,SelectionData^.Target,BitCount,
             Buffer,BufLength);
           if Buffer<>nil then
-- 
2.1.4

Index: lcl/interfaces/gtk2/gtk2callback.inc
===================================================================
--- lcl/interfaces/gtk2/gtk2callback.inc	(revision 54167)
+++ lcl/interfaces/gtk2/gtk2callback.inc	(working copy)
@@ -3571,8 +3571,8 @@
   Assert(Assigned(Buffer) and (BufLength>0), 'SetData: GTK2 clipboard Buffer=Nil or empty.');
   MemStream.Read(Buffer^,BufLength);
   // Issue #21453. gtk_selection_data_set adds the required null. Remove it here.
-  if PChar(Buffer+BufLength-1)^ = #0 then
-    dec(BufLength);
+//  if PChar(Buffer+BufLength-1)^ = #0 then  //roger
+//    dec(BufLength);
   gtk_selection_data_set(SelectionData,SelectionData^.Target,8,Buffer,BufLength);
   FreeMem(Buffer);
 end;

Index: lcl/interfaces/gtk2/gtk2callback.inc
===================================================================
--- lcl/interfaces/gtk2/gtk2callback.inc	(revision 54155)
+++ lcl/interfaces/gtk2/gtk2callback.inc	(working copy)
@@ -3564,16 +3564,29 @@
 procedure SetData(SelectionData: PGtkSelectionData; MemStream: TMemoryStream);
 var
   Buffer: Pointer;
-  BufLength: integer;
+  BufLength: gint;
+  ALastByte: Byte;
 begin
-  BufLength:=integer(MemStream.Size);
-  GetMem(Buffer,BufLength);
+  BufLength := gint(MemStream.Size);
+  GetMem(Buffer, BufLength);
   Assert(Assigned(Buffer) and (BufLength>0), 'SetData: GTK2 clipboard Buffer=Nil or empty.');
-  MemStream.Read(Buffer^,BufLength);
   // Issue #21453. gtk_selection_data_set adds the required null. Remove it here.
-  if PChar(Buffer+BufLength-1)^ = #0 then
+  if SelectionData^.length < 0 then
+  begin
+    SelectionData^.format := 8;
+    SelectionData^.length := 0;
+  end;
+  MemStream.Read(Buffer^, BufLength - 1);
+  ALastByte := MemStream.ReadByte;
+  if ALastByte <> 0 then
+  begin
+    FreeMem(Buffer);
+    GetMem(Buffer, BufLength);
+    MemStream.Position := 0;
+    MemStream.Read(Buffer^, BufLength);
+  end else
     dec(BufLength);
-  gtk_selection_data_set(SelectionData,SelectionData^.Target,8,Buffer,BufLength);
+  gtk_selection_data_set(SelectionData,SelectionData^.Target, 8, Buffer, BufLength);
   FreeMem(Buffer);
 end;