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{
This file is part of the Free Component Library.
Copyright (c) 1999-2000 by the Free Pascal development team
Implement a buffered stream.
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.
**********************************************************************}
{$mode objfpc}
{$H+}
unit bufstream;
interface
uses
Classes, SysUtils;
Const
DefaultBufferCapacity : Integer = 16; // Default buffer capacity in Kb.
Type
{ TBufStream }
TBufStream = Class(TOwnerStream)
Private
FTotalPos : Int64;
Fbuffer: Pointer;
FBufPos: Integer;
FBufSize: Integer;
FCapacity: Integer;
procedure SetCapacity(const AValue: Integer);
Protected
function GetPosition: Int64; override;
function GetSize: Int64; override;
procedure BufferError(const Msg : String);
Procedure FillBuffer; Virtual;
Procedure FlushBuffer; Virtual;
Public
Constructor Create(ASource : TStream; ACapacity: Integer);
Constructor Create(ASource : TStream);
Destructor Destroy; override;
Property Buffer : Pointer Read Fbuffer;
Property Capacity : Integer Read FCapacity Write SetCapacity;
Property BufferPos : Integer Read FBufPos; // 0 based.
Property BufferSize : Integer Read FBufSize; // Number of bytes in buffer.
end;
{ TReadBufStream }
TReadBufStream = Class(TBufStream)
Public
function Seek(const Offset: Int64; Origin: TSeekOrigin): Int64; override;
Function Read(var ABuffer; ACount : LongInt) : Integer; override;
end;
{ TWriteBufStream }
TWriteBufStream = Class(TBufStream)
Public
Destructor Destroy; override;
function Seek(const Offset: Int64; Origin: TSeekOrigin): Int64; override;
Function Write(Const ABuffer; ACount : LongInt) : Integer; override;
end;
implementation
Resourcestring
SErrCapacityTooSmall = 'Capacity is less than actual buffer size.';
SErrCouldNotFLushBuffer = 'Could not flush buffer';
SErrInvalidSeek = 'Invalid buffer seek operation';
{ TBufStream }
procedure TBufStream.SetCapacity(const AValue: Integer);
begin
if (FCapacity<>AValue) then
begin
If (AValue<FBufSize) then
BufferError(SErrCapacityTooSmall);
ReallocMem(FBuffer,AValue);
FCapacity:=AValue;
end;
end;
function TBufStream.GetPosition: Int64;
begin
Result:=FTotalPos;
end;
function TBufStream.GetSize: Int64;
begin
Result:=Source.Size;
end;
procedure TBufStream.BufferError(const Msg: String);
begin
Raise EStreamError.Create(Msg);
end;
procedure TBufStream.FillBuffer;
Var
RCount : Integer;
P : PChar;
begin
P:=Pchar(FBuffer);
// Reset at beginning if empty.
If (FBufSize-FBufPos)<=0 then
begin
FBufSize:=0;
FBufPos:=0;
end;
Inc(P,FBufSize);
RCount:=1;
while (RCount<>0) and (FBufSize<FCapacity) do
begin
RCount:=FSource.Read(P^,FCapacity-FBufSize);
Inc(P,RCount);
Inc(FBufSize,RCount);
end;
end;
procedure TBufStream.FlushBuffer;
Var
WCount : Integer;
P : PChar;
begin
P:=Pchar(FBuffer);
Inc(P,FBufPos);
WCount:=1;
While (WCount<>0) and ((FBufSize-FBufPos)>0) do
begin
WCount:=FSource.Write(P^,FBufSize-FBufPos);
Inc(P,WCount);
Inc(FBufPos,WCount);
end;
If ((FBufSize-FBufPos)<=0) then
begin
FBufPos:=0;
FBufSize:=0;
end
else
BufferError(SErrCouldNotFLushBuffer);
end;
constructor TBufStream.Create(ASource: TStream; ACapacity: Integer);
begin
Inherited Create(ASource);
SetCapacity(ACapacity);
end;
constructor TBufStream.Create(ASource: TStream);
begin
Create(ASource,DefaultBufferCapacity*1024);
end;
destructor TBufStream.Destroy;
begin
FBufSize:=0;
SetCapacity(0);
inherited Destroy;
end;
{ TReadBufStream }
function TReadBufStream.Seek(const Offset: Int64; Origin: TSeekOrigin): Int64;
begin
FakeSeekForward(Offset,Origin,FTotalPos);
Result:=FTotalPos; // Pos updated by fake read
end;
function TReadBufStream.Read(var ABuffer; ACount: LongInt): Integer;
Var
P,PB : PChar;
Avail,MSize,RCount : Integer;
begin
Result:=0;
P:=PChar(@ABuffer);
Avail:=1;
While (Result<ACount) and (Avail>0) do
begin
If (FBufSize-FBufPos<=0) then
FillBuffer;
Avail:=FBufSize-FBufPos;
If (Avail>0) then
begin
MSize:=ACount-Result;
If (MSize>Avail) then
MSize:=Avail;
PB:=PChar(FBuffer);
Inc(PB,FBufPos);
Move(PB^,P^,MSIze);
Inc(FBufPos,MSize);
Inc(P,MSize);
Inc(Result,MSize);
end;
end;
Inc(FTotalPos,Result);
end;
{ TWriteBufStream }
destructor TWriteBufStream.Destroy;
begin
FlushBuffer;
inherited Destroy;
end;
function TWriteBufStream.Seek(const Offset: Int64; Origin: TSeekOrigin): Int64;
begin
if (Offset=0) and (Origin=soCurrent) then
Result := FTotalPos
else
BufferError(SErrInvalidSeek);
end;
function TWriteBufStream.Write(const ABuffer; ACount: LongInt): Integer;
Var
P,PB : PChar;
Avail,MSize,RCount : Integer;
begin
Result:=0;
P:=PChar(@ABuffer);
While (Result<ACount) do
begin
If (FBufSize=FCapacity) then
FlushBuffer;
Avail:=FCapacity-FBufSize;
MSize:=ACount-Result;
If (MSize>Avail) then
MSize:=Avail;
PB:=PChar(FBuffer);
Inc(PB,FBufSize);
Move(P^,PB^,MSIze);
Inc(FBufSize,MSize);
Inc(P,MSize);
Inc(Result,MSize);
end;
Inc(FTotalPos,Result);
end;
end.
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