Title: A new technology for adding compression and encryption capabilities to your applications.
Question: How to add the compression and encryption capabilities to the existing project based on streams.
Answer:
I developed an application but when the work was finished, I had to compress the application data stored in a file on the disk and to add the encryption capabilities.
I tried lots of proper tools for compression and encryption. Having carried out a big investigation I found out that the most appropriate tool for me was EasyCompression Librory by AidAim Software (http://www.aidaim.com).
The key feature of the EasyCompression Library that makes the library different from all the others on the market is a one stream for compression and decompression. Usually there are two stream classes offered by the compression libraries: TCompressionStream and TDecompressionStream. TCompressionStream is write-only and strictly sequential, using Seek to move the stream pointer raises exception. Another TDecompressionStream is read-only and unidirectional, and only forward Seek is allowed. Besides, its not possible to get and set the data size. AidAim Software produced the technology that allows to use the same stream both for data compression and decompression. This universal stream class allows you to use all the properties and methods of the usual TStream, so you could read data, write data, seek in any directions, get/set data size, and at the same time some additional functions, such as: get the compressed data size, compression ratio, progress indication. Such stream is completely compatible with TStream and ensures transparent compression/decompression, i.e. the programmer works with such class as with usual TStream not caring about data size, compression algorithm, compression ratio although these parameters are also available. Use of one stream instead of two ones allows to make the programmers work faster not only in program building but also in adding the functions of compression and encryption to the existing application. Its enough just to replace your TFileStream or TMemoryStream by its analogue in the EasyCompression Library that supports all the methods, properties and behavior of TFileStream and TMemoryStream. And your application gets advanced data compression and encryption features.
Assume that firstly we used the TFileStream for data access and now wed like our file to be compressed and encrypted.
It was so:
----------
var
fs: TFileStream;
inBuf,outBuf: PChar;
offset,inSize,outSize: Integer;
begin
{buffers are allocated, necessary offsets and sizes are set}
{ let's create file }
fs := TFileStream.Create('test.dat',fmCreate);
{ write some data}
fs.WriteBuffer(outBuf^,outSize);
{ seek to needed position }
fs.Seek(offset, soFromBeginning);
{ read some data }
fs.ReadBuffer(inBuf^,inSize);
{close file }
fs.Free;
end;
Now it will be so:
------------------
var
fs: TECLFileStream;
inBuf,outBuf: PChar;
offset,inSize,outSize: Integer;
begin
{buffers are allocated, necessary offsets and sizes are set}
{ let's create compressed and encrypted file}
fs := TECLFileStream.Create('test.dat', fmCreate, 'Password', eclFastest);
{ write some data }
fs.WriteBuffer(outBuf^,outSize);
{ seek to needed position }
fs.Seek(offset, soFromBeginning);
{ read some data }
fs.ReadBuffer(inBuf^,inSize);
{close file }
fs.Free;
end;
You see that the changes in the program code are minimal and you get easily the transparent compression and encryption.
Another example. Low memory consumption.
In my work I met a need to reduce the memory consumption. I used the TMemoryStream for working with some object in memory. Using the TECLMemoryStream I get less memory consumption since the object is packed in memory keeping the high access speed.
One more example. Blob fields compression.
In my another project, I used the Blob fields in the Paradox database. I saw I could reduce the database size in 3 10 times by compression of Memo and Graphic fields. Replacement of the TBlobStream by the TECLStream helped me in this case very well. The example of such substitution I found at the Graphic Demo in the EasyCompression Library delivery set.