path: root/packages/fcl-base/src/advancedipc.pp

{
    This file is part of the Free Component Library (FCL)
    Copyright (c) 2015 by Ondrej Pokorny

    Unit implementing two-way (request/response) IPC between 1 server and more
    clients, based on files.
    The order of message processing is not deterministic (if there are more
    pending messages, the server won't process them in the order they have
    been sent to the server.
    SendRequest and PostRequest+PeekResponse sequences from 1 client are
    blocking and processed in correct order.

    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.

 **********************************************************************}

unit AdvancedIPC;

{$mode objfpc}
{$H+}

interface

uses
  {$IFDEF UNIX}
  baseunix,
  {$endif}
  sysutils, Classes, singleinstance;

const
  HEADER_VERSION = 2;

type
  TMessageType = LongInt;
  TMessageHeader = packed record
    HeaderVersion: Byte;
    FileLock: Byte;//0 = unlocked, 1 = locked
    MsgType: TMessageType;
    MsgLen: Integer;
    MsgVersion: Integer;
  end;

  TFileHandle = Classes.THandle;

  TReleaseHandleStream = class(THandleStream)
  public
    destructor Destroy; override;
  end;

  TIPCBase = class(TComponent)
  private
    FGlobal: Boolean;
    FFileName: string;
    FServerID: string;
    FMessageVersion: Integer;
  protected
    class function ServerIDToFileName(const aServerID: string; const aGlobal: Boolean): string;
    function GetResponseFileName(const aRequestID: Integer): string;
    function GetResponseFileName(const aRequestFileName: string): string;
    function GetPeekedRequestFileName(const aRequestID: Integer): string;
    function GetPeekedRequestFileName(const aRequestFileName: string): string;
    function GetRequestPrefix: string;
    function GetRequestFileName(const aRequestID: Integer): string;
    function RequestFileNameToID(const aFileName: string): Integer;
    function RequestExists(const aRequestFileName: string): Boolean;

    procedure SetServerID(const aServerID: string); virtual;
    procedure SetGlobal(const aGlobal: Boolean); virtual;

    function CanReadMessage(const aFileName: string; out outStream: TStream; out outMsgType: TMessageType; out outMsgLen: Integer): Boolean;
    procedure DoPostMessage(const aFileName: string; const aMsgType: TMessageType; const aStream: TStream); overload;
    procedure DoPostMessage(const aFileStream: TFileStream; const aMsgType: TMessageType; const aStream: TStream); overload;
    function DoReadMessage(const aFileName: string; const aStream: TStream; out outMsgType: TMessageType): Boolean;

    property FileName: string read FFileName;
  public
    class procedure FindRunningServers(const aServerIDPrefix: string;
      const outServerIDs: TStrings; const aGlobal: Boolean = False);
    class function ServerRunning(const aServerID: string; const aGlobal: Boolean = False): Boolean; overload;
  public
    //ServerID: name/ID of the server. Use only ['a'..'z', 'A'..'Z', '0'..'9', '_'] characters
    property ServerID: string read FServerID write SetServerID;
    //Global: if true, processes from different users can communicate; false, processes only from current user can communicate
    property Global: Boolean read FGlobal write SetGlobal;
    //MessageVersion: only messages with the same MessageVersion can be delivered between server/client
    property MessageVersion: Integer read FMessageVersion write FMessageVersion;
  end;

  TIPCClient = class(TIPCBase)
  private
    FLastRequestID: Integer;

    function CreateUniqueRequest(out outFileStream: TFileStream): Integer;
    function DoPeekResponse(const aResponseFileName: string; const aStream: TStream; out outMsgType: TMessageType; const aTimeOut: Integer): Boolean;
  public
    constructor Create(aOwner: TComponent); override;
  public
    //post request to server, do not wait until request is peeked; returns request ID
    function PostRequest(const aMsgType: TMessageType; const aStream: TStream): Integer;
    //send request to server, wait until request is peeked; returns True if request was peeked within the aTimeOut limit
    function SendRequest(const aMsgType: TMessageType; const aStream: TStream; const aTimeOut: Integer): Boolean;
    function SendRequest(const aMsgType: TMessageType; const aStream: TStream; const aTimeOut: Integer; out outRequestID: Integer): Boolean;
    //peek a response from last request from this client
    function PeekResponse(const aStream: TStream; out outMsgType: TMessageType): Boolean; overload;
    function PeekResponse(const aStream: TStream; out outMsgType: TMessageType; const aTimeOut: Integer): Boolean; overload;
    //peek a response from request by ID
    function PeekResponse(const aRequestID: Integer; const aStream: TStream; out outMsgType: TMessageType): Boolean; overload;
    function PeekResponse(const aRequestID: Integer; const aStream: TStream; out outMsgType: TMessageType; const aTimeOut: Integer): Boolean; overload;
    //delete last request from this client, returns true if request file existed and was deleted
    function DeleteRequest: Boolean; overload;
    //delete request by ID, returns true if request existed file and was deleted
    function DeleteRequest(const aRequestID: Integer): Boolean; overload;
    //check if server is running
    function ServerRunning: Boolean; overload;
  end;

  TIPCServer = class(TIPCBase)
  private
    FFileHandle: TFileHandle;
    FActive: Boolean;

    function FindFirstRequest(out outFileName: string; out outStream: TStream; out outMsgType: TMessageType; out outMsgLen: Integer): Integer;

  protected
    procedure SetServerID(const aServerID: string); override;
    procedure SetGlobal(const aGlobal: Boolean); override;
  public
    constructor Create(aOwner: TComponent); override;
    destructor Destroy; override;
  public
    //peek request and read the message into a stream
    function PeekRequest(const aStream: TStream; out outMsgType: TMessageType): Boolean; overload;
    function PeekRequest(const aStream: TStream; out outRequestID: Integer; out outMsgType: TMessageType): Boolean; overload;
    function PeekRequest(const aStream: TStream; out outRequestID: Integer; out outMsgType: TMessageType; const aTimeOut: Integer): Boolean; overload;
    //only peek request, you have to read/delete the request manually with ReadRequest/DeleteRequest
    function PeekRequest(out outMsgType: TMessageType): Boolean; overload;
    function PeekRequest(out outRequestID: Integer; out outMsgType: TMessageType): Boolean; overload;
    function PeekRequest(out outRequestID: Integer; out outMsgType: TMessageType; const aTimeOut: Integer): Boolean; overload;
    //read a peeked request (that hasn't been read yet)
    function ReadRequest(const aRequestID: Integer; const aStream: TStream): Boolean;
    //delete a peeked request (that hasn't been read yet), returns true if request file existed and was deleted
    function DeleteRequest(const aRequestID: Integer): Boolean;

    //post response to a request
    procedure PostResponse(const aRequestID: Integer; const aMsgType: TMessageType; const aStream: TStream);

    //find the highest request ID from all pending requests
    function FindHighestPendingRequestId: Integer;
    //get the pending request count
    function GetPendingRequestCount: Integer;

    //start server: returns true if unique and started
    function StartServer(const aDeletePendingRequests: Boolean = True): Boolean;
    //stop server: returns true if stopped
    function StopServer(const aDeletePendingRequests: Boolean = True): Boolean;

    //delete all pending requests and responses
    procedure DeletePendingRequests;
  public
    //true if server runs (was started)
    property Active: Boolean read FActive;
  end;

  EICPException = class(Exception);

resourcestring
  SErrInvalidServerID = 'Invalid server ID "%s". Please use only alphanumerical characters and underlines.';
  SErrSetGlobalActive = 'You cannot change the global property when the server is active.';
  SErrSetServerIDActive = 'You cannot change the server ID when the server is active.';

implementation

type
  TIPCSearchRec = TRawByteSearchRec;

const
  {$IFDEF UNIX}
  GLOBAL_RIGHTS = S_IRUSR or S_IWUSR or S_IRGRP or S_IWGRP or S_IROTH or S_IWOTH;
  {$ELSE}
  GLOBAL_RIGHTS = 0;
  {$ENDIF}

var
  CreateUniqueRequestCritSec: TRTLCriticalSection;

{ TIPCBase }

function TIPCBase.CanReadMessage(const aFileName: string; out
  outStream: TStream; out outMsgType: TMessageType; out outMsgLen: Integer
  ): Boolean;
var
  xFileHandle: TFileHandle;
  xHeader: TMessageHeader;
begin
  outStream := nil;
  outMsgType := -1;
  outMsgLen := 0;
  Result := FileExists(aFileName);
  if not Result then
    Exit;

  xFileHandle := FileOpen(aFileName, fmOpenRead or fmShareExclusive);
  Result := xFileHandle <> feInvalidHandle;
  if not Result then
    Exit;

  outStream := TReleaseHandleStream.Create(xFileHandle);

  Result := (outStream.Size >= SizeOf(xHeader));
  if not Result then
  begin
    FreeAndNil(outStream);
    Exit;
  end;

  outStream.ReadBuffer(xHeader{%H-}, SizeOf(xHeader));
  Result :=
    (xHeader.HeaderVersion = HEADER_VERSION) and (xHeader.FileLock = 0) and
    (xHeader.MsgVersion = MessageVersion) and
    (outStream.Size = Int64(SizeOf(xHeader))+Int64(xHeader.MsgLen));
  if not Result then
  begin
    FreeAndNil(outStream);
    Exit;
  end;
  outMsgType := xHeader.MsgType;
  outMsgLen := xHeader.MsgLen;
end;

function TIPCBase.DoReadMessage(const aFileName: string;
  const aStream: TStream; out outMsgType: TMessageType): Boolean;
var
  xStream: TStream;
  xMsgLen: Integer;
begin
  aStream.Size := 0;
  xStream := nil;
  try
    Result := CanReadMessage(aFileName, xStream, outMsgType, xMsgLen);
    if Result then
    begin
      if xMsgLen > 0 then
        aStream.CopyFrom(xStream, xMsgLen);
      FreeAndNil(xStream);
      aStream.Position := 0;
      DeleteFile(aFileName);
    end;
  finally
    xStream.Free;
  end;
end;

function TIPCBase.RequestExists(const aRequestFileName: string): Boolean;
begin
  Result :=
    (FileExists(aRequestFileName) or
     FileExists(GetResponseFileName(aRequestFileName)) or
     FileExists(GetPeekedRequestFileName(aRequestFileName)));
end;

class function TIPCBase.ServerRunning(const aServerID: string;
  const aGlobal: Boolean): Boolean;
var
  xServerFileHandle: TFileHandle;
  xFileName: String;
begin
  xFileName := ServerIDToFileName(aServerID, aGlobal);
  Result := FileExists(xFileName);
  if Result then
  begin//+ check -> we should not be able to access the file
    xServerFileHandle := FileCreate(xFileName, fmOpenReadWrite or fmShareExclusive, GLOBAL_RIGHTS);
    Result := (xServerFileHandle=feInvalidHandle);
    if not Result then
      FileClose(xServerFileHandle);
  end;
end;

class function TIPCBase.ServerIDToFileName(const aServerID: string;
  const aGlobal: Boolean): string;
begin
  Result := GetTempDir(aGlobal)+aServerID;
end;

procedure TIPCBase.SetGlobal(const aGlobal: Boolean);
begin
  if FGlobal = aGlobal then Exit;

  FGlobal := aGlobal;
  FFileName := ServerIDToFileName(FServerID, FGlobal);
end;

procedure TIPCBase.DoPostMessage(const aFileName: string;
  const aMsgType: TMessageType; const aStream: TStream);
var
  xStream: TFileStream;
begin
  xStream := TFileStream.Create(aFileName, fmCreate or fmShareExclusive, GLOBAL_RIGHTS);
  try
    DoPostMessage(xStream, aMsgType, aStream);
  finally
    xStream.Free;
  end;
end;

procedure TIPCBase.DoPostMessage(const aFileStream: TFileStream;
  const aMsgType: TMessageType; const aStream: TStream);
var
  xHeader: TMessageHeader;
begin
  xHeader.HeaderVersion := HEADER_VERSION;
  xHeader.FileLock := 1;//locking
  xHeader.MsgType := aMsgType;
  if Assigned(aStream) then
    xHeader.MsgLen := aStream.Size-aStream.Position
  else
    xHeader.MsgLen := 0;
  xHeader.MsgVersion := MessageVersion;

  aFileStream.WriteBuffer(xHeader, SizeOf(xHeader));
  if Assigned(aStream) and (aStream.Size-aStream.Position > 0) then
    aFileStream.CopyFrom(aStream, aStream.Size-aStream.Position);

  aFileStream.Position := 0;//unlocking
  xHeader.FileLock := 0;
  aFileStream.WriteBuffer(xHeader, SizeOf(xHeader));
  aFileStream.Seek(0, soEnd);
end;

function TIPCBase.RequestFileNameToID(const aFileName: string): Integer;
begin
  //the function prevents all responses/temp files to be handled
  //only valid response files are returned
  if (Length(aFileName) > 9) and (aFileName[Length(aFileName)-8] = '-') then
    Result := StrToIntDef('$'+Copy(aFileName, Length(aFileName)-7, 8), -1)
  else
    Result := -1;
end;

class procedure TIPCBase.FindRunningServers(const aServerIDPrefix: string;
  const outServerIDs: TStrings; const aGlobal: Boolean);
var
  xRec: TIPCSearchRec;
begin
  if FindFirst(ServerIDToFileName(aServerIDPrefix+AllFilesMask, aGlobal), faAnyFile, xRec) = 0 then
  begin
    repeat
      if (Pos('-', xRec.Name) = 0) and//file that we found is a pending message
         ServerRunning(xRec.Name, aGlobal)
      then
        outServerIDs.Add(xRec.Name);
    until FindNext(xRec) <> 0;
  end;
  FindClose(xRec);
end;

function TIPCBase.GetPeekedRequestFileName(const aRequestID: Integer): string;
begin
  Result := GetPeekedRequestFileName(GetRequestFileName(aRequestID));
end;

function TIPCBase.GetPeekedRequestFileName(const aRequestFileName: string
  ): string;
begin
  Result := aRequestFileName+'-t';
end;

function TIPCBase.GetRequestFileName(const aRequestID: Integer): string;
begin
  Result := GetRequestPrefix+IntToHex(aRequestID, 8);
end;

function TIPCBase.GetRequestPrefix: string;
begin
  Result := FFileName+'-';
end;

function TIPCBase.GetResponseFileName(const aRequestID: Integer): string;
begin
  Result := GetResponseFileName(GetRequestFileName(aRequestID));
end;

function TIPCBase.GetResponseFileName(const aRequestFileName: string): string;
begin
  Result := aRequestFileName+'-r';
end;

procedure TIPCBase.SetServerID(const aServerID: string);
var
  I: Integer;
begin
  if FServerID = aServerID then Exit;

  for I := 1 to Length(aServerID) do
  if not (aServerID[I] in ['a'..'z', 'A'..'Z', '0'..'9', '_']) then
    raise EICPException.CreateFmt(SErrInvalidServerID , [aServerID]);

  FServerID := aServerID;

  FFileName := ServerIDToFileName(FServerID, FGlobal);
end;

{ TIPCClient }

constructor TIPCClient.Create(aOwner: TComponent);
begin
  inherited Create(aOwner);

  FLastRequestID := -1;
end;

function TIPCClient.DeleteRequest(const aRequestID: Integer): Boolean;
var
  xRequestFileName: string;
begin
  xRequestFileName := GetRequestFileName(aRequestID);
  Result := DeleteFile(xRequestFileName);
  if (aRequestID = FLastRequestID) and not FileExists(xRequestFileName) then
    FLastRequestID := -1;
end;

function TIPCClient.DeleteRequest: Boolean;
begin
  if FLastRequestID >= 0 then
    Result := DeleteRequest(FLastRequestID)
  else
    Result := False;
end;

function TIPCClient.DoPeekResponse(const aResponseFileName: string;
  const aStream: TStream; out outMsgType: TMessageType; const aTimeOut: Integer
  ): Boolean;
var
  xStart: QWord;
begin
  aStream.Size := 0;
  Result := False;
  xStart := GetTickCount64;
  repeat
    if DoReadMessage(aResponseFileName, aStream, outMsgType) then
      Exit(True)
    else if aTimeOut > 20 then
      Sleep(10);
  until (GetTickCount64-xStart > aTimeOut);
end;

function TIPCClient.CreateUniqueRequest(out outFileStream: TFileStream): Integer;
var
  xFileName: string;
begin
  outFileStream := nil;
  EnterCriticalsection(CreateUniqueRequestCritSec);
  try
    Randomize;
    repeat
      //if Randomize/Random is started from 2 processes at exactly same moment, it returns the same number! -> prevent duplicates by xor GetProcessId
      //the result must be of range 0..$7FFFFFFF (High(Integer))
      Result := Integer((PtrInt(Random($7FFFFFFF)) xor PtrInt(GetProcessID)) and $7FFFFFFF);
      xFileName := GetRequestFileName(Result);
    until not RequestExists(xFileName);

    outFileStream := TFileStream.Create(xFileName, fmCreate or fmShareExclusive, GLOBAL_RIGHTS);
  finally
    LeaveCriticalsection(CreateUniqueRequestCritSec);
  end;
end;

function TIPCClient.PeekResponse(const aRequestID: Integer;
  const aStream: TStream; out outMsgType: TMessageType): Boolean;
begin
  Result := DoReadMessage(GetResponseFileName(aRequestID), aStream, outMsgType);
end;

function TIPCClient.PeekResponse(const aRequestID: Integer;
  const aStream: TStream; out outMsgType: TMessageType; const aTimeOut: Integer
  ): Boolean;
begin
  Result := DoPeekResponse(GetResponseFileName(aRequestID), aStream, outMsgType, aTimeOut);
end;

function TIPCClient.PeekResponse(const aStream: TStream; out
  outMsgType: TMessageType): Boolean;
begin
  Result := DoReadMessage(GetResponseFileName(FLastRequestID), aStream, outMsgType);
end;

function TIPCClient.PeekResponse(const aStream: TStream; out
  outMsgType: TMessageType; const aTimeOut: Integer): Boolean;
begin
  Result := DoPeekResponse(GetResponseFileName(FLastRequestID), aStream, outMsgType, aTimeOut);
end;

function TIPCClient.PostRequest(const aMsgType: TMessageType;
  const aStream: TStream): Integer;
var
  xRequestFileStream: TFileStream;
begin
  xRequestFileStream := nil;
  try
    Result := CreateUniqueRequest(xRequestFileStream);
    DoPostMessage(xRequestFileStream, aMsgType, aStream);
  finally
    xRequestFileStream.Free;
  end;
  FLastRequestID := Result;
end;

function TIPCClient.SendRequest(const aMsgType: TMessageType;
  const aStream: TStream; const aTimeOut: Integer): Boolean;
var
  xRequestID: Integer;
begin
  Result := SendRequest(aMsgType, aStream, aTimeOut, xRequestID);
end;

function TIPCClient.SendRequest(const aMsgType: TMessageType;
  const aStream: TStream; const aTimeOut: Integer; out outRequestID: Integer
  ): Boolean;
var
  xStart: QWord;
  xRequestFileName: string;
begin
  outRequestID := PostRequest(aMsgType, aStream);
  Result := False;

  xRequestFileName := GetRequestFileName(outRequestID);
  xStart := GetTickCount64;
  repeat
    if not FileExists(xRequestFileName) then
      Exit(True)
    else if aTimeOut > 20 then
      Sleep(10);
  until (GetTickCount64-xStart > aTimeOut);
end;

function TIPCClient.ServerRunning: Boolean;
begin
  Result := ServerRunning(ServerID, Global);
end;

{ TReleaseHandleStream }

destructor TReleaseHandleStream.Destroy;
begin
  FileClose(Handle);

  inherited Destroy;
end;

{ TIPCServer }

procedure TIPCServer.DeletePendingRequests;
var
  xRec: TIPCSearchRec;
  xDir: string;
begin
  xDir := ExtractFilePath(FFileName);
  if FindFirst(GetRequestPrefix+AllFilesMask, faAnyFile, xRec) = 0 then
  begin
    repeat
      DeleteFile(xDir+xRec.Name);
    until FindNext(xRec) <> 0;
  end;
  FindClose(xRec);
end;

function TIPCServer.DeleteRequest(const aRequestID: Integer): Boolean;
begin
  Result := DeleteFile(GetPeekedRequestFileName(aRequestID));
end;

constructor TIPCServer.Create(aOwner: TComponent);
begin
  inherited Create(aOwner);

  FFileHandle := feInvalidHandle;
end;

destructor TIPCServer.Destroy;
begin
  if Active then
    StopServer;

  inherited Destroy;
end;

function TIPCServer.FindFirstRequest(out outFileName: string; out
  outStream: TStream; out outMsgType: TMessageType; out outMsgLen: Integer
  ): Integer;
var
  xRec: TIPCSearchRec;
begin
  outFileName := '';
  outStream := nil;
  outMsgType := -1;
  outMsgLen := 0;
  Result := -1;
  if FindFirst(GetRequestPrefix+AllFilesMask, faAnyFile, xRec) = 0 then
  begin
    repeat
      Result := RequestFileNameToID(xRec.Name);
      if Result >= 0 then
      begin
        outFileName := GetRequestFileName(Result);
        if not CanReadMessage(outFileName, outStream, outMsgType, outMsgLen) then
          Result := -1;
      end;
    until (Result >= 0) or (FindNext(xRec) <> 0);
  end;
  FindClose(xRec);
end;

function TIPCServer.FindHighestPendingRequestId: Integer;
var
  xRec: TIPCSearchRec;
  xRequestID: LongInt;
begin
  Result := -1;
  if FindFirst(GetRequestPrefix+AllFilesMask, faAnyFile, xRec) = 0 then
  begin
    repeat
      xRequestID := RequestFileNameToID(xRec.Name);
      if xRequestID > Result then
        Result := xRequestID;
    until FindNext(xRec) <> 0;
  end;
  FindClose(xRec);
end;

function TIPCServer.GetPendingRequestCount: Integer;
var
  xRec: TIPCSearchRec;
begin
  Result := 0;
  if FindFirst(GetRequestPrefix+AllFilesMask, faAnyFile, xRec) = 0 then
  begin
    repeat
      if RequestFileNameToID(xRec.Name) >= 0 then
        Inc(Result);
    until FindNext(xRec) <> 0;
  end;
  FindClose(xRec);
end;

function TIPCServer.PeekRequest(out outRequestID: Integer; out
  outMsgType: TMessageType): Boolean;
var
  xStream: TStream;
  xMsgLen: Integer;
  xMsgFileName: string;
begin
  outMsgType := -1;
  xMsgFileName := '';
  xStream := nil;
  try
    outRequestID := FindFirstRequest(xMsgFileName, xStream, outMsgType, xMsgLen);
    Result := outRequestID >= 0;
    if Result then
    begin
      FreeAndNil(xStream);
      RenameFile(xMsgFileName, GetPeekedRequestFileName(xMsgFileName));
    end;
  finally
    xStream.Free;
  end;
end;

function TIPCServer.PeekRequest(out outRequestID: Integer; out
  outMsgType: TMessageType; const aTimeOut: Integer): Boolean;
var
  xStart: QWord;
begin
  Result := False;
  xStart := GetTickCount64;
  repeat
    if PeekRequest(outRequestID, outMsgType) then
      Exit(True)
    else if aTimeOut > 20 then
      Sleep(10);
  until (GetTickCount64-xStart > aTimeOut);
end;

function TIPCServer.PeekRequest(out outMsgType: TMessageType): Boolean;
var
  xRequestID: Integer;
begin
  Result := PeekRequest(xRequestID, outMsgType);
end;

function TIPCServer.PeekRequest(const aStream: TStream; out outRequestID: Integer;
  out outMsgType: TMessageType): Boolean;
begin
  Result := PeekRequest(outRequestID, outMsgType);
  if Result then
    Result := ReadRequest(outRequestID, aStream);
end;

function TIPCServer.PeekRequest(const aStream: TStream; out outRequestID: Integer;
  out outMsgType: TMessageType; const aTimeOut: Integer): Boolean;
begin
  Result := PeekRequest(outRequestID, outMsgType, aTimeOut);
  if Result then
    Result := ReadRequest(outRequestID, aStream);
end;

function TIPCServer.PeekRequest(const aStream: TStream; out
  outMsgType: TMessageType): Boolean;
var
  xRequestID: Integer;
begin
  Result := PeekRequest(aStream, xRequestID, outMsgType);
end;

procedure TIPCServer.PostResponse(const aRequestID: Integer;
  const aMsgType: TMessageType; const aStream: TStream);
begin
  DoPostMessage(GetResponseFileName(aRequestID), aMsgType, aStream);
end;

function TIPCServer.ReadRequest(const aRequestID: Integer; const aStream: TStream
  ): Boolean;
var
  xMsgType: TMessageType;
begin
  Result := DoReadMessage(GetPeekedRequestFileName(aRequestID), aStream, xMsgType);
end;

procedure TIPCServer.SetGlobal(const aGlobal: Boolean);
begin
  if Active then
    raise EICPException.Create(SErrSetGlobalActive);

  inherited SetGlobal(aGlobal);
end;

procedure TIPCServer.SetServerID(const aServerID: string);
begin
  if Active then
    raise EICPException.Create(SErrSetServerIDActive);

  inherited SetServerID(aServerID);
end;

function TIPCServer.StartServer(const aDeletePendingRequests: Boolean): Boolean;
begin
  if Active then
    Exit(True);

  FFileHandle := FileCreate(FFileName, fmCreate or fmShareExclusive, GLOBAL_RIGHTS);
  Result := (FFileHandle<>feInvalidHandle);
  FActive := Result;
  if Result and aDeletePendingRequests then
    DeletePendingRequests;
end;

function TIPCServer.StopServer(const aDeletePendingRequests: Boolean): Boolean;
begin
  if not Active then
    Exit(True);

  if FFileHandle<>feInvalidHandle then
    FileClose(FFileHandle);
  Result := DeleteFile(FFileName);

  if aDeletePendingRequests then
    DeletePendingRequests;

  FActive := False;
end;

initialization
  InitCriticalSection(CreateUniqueRequestCritSec);

finalization
  DoneCriticalsection(CreateUniqueRequestCritSec);

end.