* Null stream implementation

git-svn-id: trunk@25495 -

.gitattributes

@@ -1947,6 +1947,7 @@ packages/fcl-base/src/iostream.pp svneol=native#text/plain
 packages/fcl-base/src/maskutils.pp svneol=native#text/plain
 packages/fcl-base/src/netware/custapp.inc svneol=native#text/plain
 packages/fcl-base/src/netwlibc/custapp.inc svneol=native#text/plain
+packages/fcl-base/src/nullstream.pp svneol=native#text/plain
 packages/fcl-base/src/os2/custapp.inc svneol=native#text/plain
 packages/fcl-base/src/os2/eventlog.inc svneol=native#text/plain
 packages/fcl-base/src/pooledmm.pp svneol=native#text/plain

packages/fcl-base/src/nullstream.pp

@@ -0,0 +1,122 @@
+{
+    This file is part of the Free Component Library (FCL)
+    Copyright (c) 1999-2000 by Michael Van Canneyt and Florian Klaempfl
+
+    See the file COPYING.FPC, included in this distribution,
+    for details about the copyright.
+
+    This program 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.
+
+ **********************************************************************}
+{$mode objfpc}
+{ Fake stream that always returns empty data. Can be written to and will discard
+all data.
+Emulates a memorystream as far as needed: by writing past the end you can
+increase its size; reading past the end gives an error}
+
+unit nullstream;
+
+interface
+
+uses Classes;
+
+type
+  ENullStreamError = class(EStreamError);
+
+  { TNullStream }
+
+  TNullStream = class(THandleStream)
+  private
+    FPos : Int64;
+    FSize: Int64;
+  protected
+    Function GetSize : int64; override;
+    procedure SetSize(Const AValue: Int64); override;
+    function  GetPosition: Int64; override;
+    procedure InvalidSeek; override;
+  public
+    function Read(var Buffer; Count : LongInt) : Longint; override;
+    function Write(const Buffer; Count : LongInt) : LongInt; override;
+    function Seek(const Offset: int64; Origin: TSeekOrigin): int64; override;
+    constructor Create;
+  end;
+
+implementation
+
+const
+  SInvalidOperation = 'Cannot perform this operation on a NullStream.';
+
+Function TNullStream.GetSize : int64;
+
+begin
+  Result:=FSize;
+end;
+
+procedure TNullStream.SetSize(const AValue: Int64);
+begin
+  FSize:=AValue;
+  if FPos>FSize then
+    FPos:=FSize;
+end;
+
+function TNullStream.GetPosition: Int64;
+begin
+  Result:=FPos;
+end;
+
+procedure TNullStream.InvalidSeek;
+begin
+  raise ENullStreamError.Create(SInvalidOperation);
+end;
+
+function TNullStream.Read(var Buffer; Count : LongInt) : Longint;
+var
+  RealCount: longint;
+begin
+  if (FPos+Count)>FSize then
+    RealCount:=FSize-FPos
+  else
+    RealCount:=Count;
+  FillChar(Buffer,RealCount,0);
+  Result:=RealCount;
+  Inc(FPos,RealCount);
+end;
+
+function TNullStream.Write(const Buffer; Count : LongInt) : LongInt;
+begin
+  Inc(FPos,Count);
+  // Emulate a memorystream: increase size if needed
+  If FPos>Fsize then
+    FSize:=FPos;
+end;
+
+
+function TNullStream.Seek(const Offset: int64; Origin: TSeekOrigin): int64;
+var
+  DesiredPos: int64;
+begin
+  if (Origin=soCurrent) and (Offset=0) then
+    Result:=FPos
+  else
+    begin
+    case Origin of
+      soCurrent: DesiredPos:=FPos+Offset;
+      soBeginning: DesiredPos:=Offset;
+      soEnd: DesiredPos:=FSize-Offset;
+    end;
+    if (DesiredPos<0) or (DesiredPos>FSize) then
+      InvalidSeek;
+    FPos:=DesiredPos;
+    end;
+end;
+
+constructor TNullStream.Create;
+begin
+  inherited create(0);
+  FPos:=0;
+  FSize:=0;
+end;
+
+end.