{
* UUserDBBackup.pas
*
* Implements a class that can create and restore backups of the user database.
*
* v1.0 of 13 Sep 2008 - Original version.
* v1.1 of 22 May 2009 - Fixed bug where restoring files greater than 32Kb
* caused a stream read error. Changed file format to
* ver 2 and kept ability to read v1 files.
*
*
* ***** BEGIN LICENSE BLOCK *****
*
* Version: MPL 1.1
*
* The contents of this file are subject to the Mozilla Public License Version
* 1.1 (the "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS" basis,
* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for
* the specific language governing rights and limitations under the License.
*
* The Original Code is UUserDBBackup.pas
*
* The Initial Developer of the Original Code is Peter Johnson
* (http://www.delphidabbler.com/).
*
* Portions created by the Initial Developer are Copyright (C) 2008-2009 Peter
* Johnson. All Rights Reserved.
*
* ***** END LICENSE BLOCK *****
}
unit UUserDBBackup;
interface
type
{
TUserDBBackup:
Class that can create and restore backups of the user database. Backups are
single files.
}
TUserDBBackup = class(TObject)
strict private
var
fBackupFile: string; // Name of backup file
fUserDBDir: string; // User database directory}
const
cWatermark = SmallInt($FFFF); // File watermark (v2 and later)
function UserDBFileSpec(const FileName: string): string;
{Builds full path to a file in user database directory.
@param FileName [in] Base name of file.
@return Fully specified file name.
}
public
constructor Create(const BackupFile: string);
{Class constructor. Sets up object to backup to a specified file.
@param BackupFile [in] Name of backup file.
}
procedure Backup;
{Creates a backup of user database in a single file.
}
procedure Restore;
{Restores user database from a backup file.
}
end;
implementation
uses
// Delphi
SysUtils, Classes,
// Project
UAppInfo, UCheckSum, UDataStreamReader, UDataStreamWriter, UDOSDateTime,
UExceptions, UUtils;
{
User database backup file format
--------------------------------
File compriises text characters. Numbers are encoded in hex format. There are
two formats:
Version 1 Format
----------------
FileCount: SmallInt - number of files encoded in backup file
followed by FileCount file records of:
Name: SizedString; - name of file without path information
FileDate: LongInt; - file's modification date (DOS file stamp as
LongInt).
MD5: String[32]; - MD5 checksum of original file on server
(MD5 of Content should match this value)
Content: SizedString; - file contents
Version 2 Format
----------------
$FFFF - Indicator of post-v1 file type
$0002 - Indicator for v2 file type
(and later versions will increment this
FileCount: SmallInt - number of files encoded in backup file
followed by FileCount file records of:
Name: SizedString; - name of file without path information
FileDate: LongInt; - file's modification date (DOS file stamp as
LongInt).
MD5: String[32]; - MD5 checksum of original file on server
(MD5 of Content should match this value)
Content: SizedLongString; - file contents
Data types
----------
SmallInt - 16 bit integer encoded as 4 hex digits
LongInt - 32 bit integer encoded as 8 hex digits
SizedString - SmallInt specifying string length followed by specified
number of characters
SizedLongString - LongInt specifying string length followed by specified
number of characters
String[32] - 32 character fixed length string
}
{ TUserDBBackup }
procedure TUserDBBackup.Backup;
{Creates a backup of user database in a single file.
}
var
Writer: TDataStreamWriter; // object used to write data to stream
Files: TStringList; // list of files in database directory
FileName: string; // references each file in database
Content: string; // content of each database file
DOSDateTime: IDOSDateTime; // date stamp of each database file
begin
Files := nil;
// Create output stream to backup file
Writer := TDataStreamWriter.Create(
TFileStream.Create(fBackupFile, fmCreate), True
);
try
// Get list of files in database and write number of files to output
Files := TStringList.Create;
ListFiles(fUserDBDir, '*.*', Files, False);
Writer.WriteSmallInt(cWatermark); // file marker
Writer.WriteSmallInt($0002); // file version
Writer.WriteSmallInt(Files.Count); // number of files
// Write details of each file to output: file name, date stamp, checksum and
// content
for FileName in Files do
begin
Writer.WriteSizedString(FileName);
DOSDateTime := TDOSDateTimeFactory.CreateFromFile(
UserDBFileSpec(FileName)
);
Writer.WriteLongInt(DOSDateTime.DateStamp);
Content := FileToString(UserDBFileSpec(FileName));
Writer.WriteString(TCheckSum.Calculate(Content), 32);
Writer.WriteSizedLongString(Content);
end;
finally
FreeAndNil(Files);
FreeAndNil(Writer);
end;
end;
constructor TUserDBBackup.Create(const BackupFile: string);
{Class constructor. Sets up object to backup to a specified file.
@param BackupFile [in] Name of backup file.
}
begin
inherited Create;
fBackupFile := BackupFile;
fUserDBDir := PathToDir(TAppInfo.UserDataDir);
end;
procedure TUserDBBackup.Restore;
{Restores user database from a backup file.
}
var
Reader: TDataStreamReader; // object used to read data from file
FileCount: Integer; // number of files to restore
Idx: Integer; // loops through all files in backup
FileName: string; // name of file to restore
MD5: string; // checksum of file to restore
Content: string; // content of file to restore
DOSDateTime: IDOSDateTime; // date stamp of file to restore
HeaderWord: SmallInt; // first word value in file
Version: SmallInt; // file version
resourcestring
// Error message
sBadFileContent = 'Invalid content for file "%s"';
begin
// Make sure database folder exists
EnsureFolders(fUserDBDir);
// Create reader to access data in backup file
Reader := TDataStreamReader.Create(
TFileStream.Create(fBackupFile, fmOpenRead or fmShareDenyNone)
);
try
// Get number of files stored in backup file and process each one
// Read 1st word of file. If it is $FFFF we have v2 or later file, otherwise
// it's v1
HeaderWord := Reader.ReadSmallInt;
if HeaderWord = cWatermark then
begin
// v2 or later: read version then file count
Version := Reader.ReadSmallInt;
FileCount := Reader.ReadSmallInt;
end
else
begin
// v1: file count was first word of file
Version := 1;
FileCount := HeaderWord;
end;
for Idx := 1 to FileCount do
begin
// Get file details: name, date stamp, checksum and content
FileName := UserDBFileSpec(Reader.ReadSizedString);
DOSDateTime := TDOSDateTimeFactory.CreateFromDOSTimeStamp(
Reader.ReadLongInt
);
MD5 := Reader.ReadString(32);
if Version = 1 then
Content := Reader.ReadSizedString
else
Content := Reader.ReadSizedLongString;
if not TCheckSum.Compare(Content, MD5) then
raise ECodeSnip.CreateFmt(sBadFileContent, [FileName]);
// Write file and set date stamp
StringToFile(Content, FileName);
DOSDateTime.ApplyToFile(FileName);
end;
finally
FreeAndNil(Reader);
end;
end;
function TUserDBBackup.UserDBFileSpec(const FileName: string): string;
{Builds full path to a file in user database directory.
@param FileName [in] Base name of file.
@return Fully specified file name.
}
begin
Result := DirToPath(fUserDBDir) + FileName;
end;
end.
