Question

Why the result of GZip algorithm is not same in Android and .Net?

My code in android:

    public static String compressString(String str) {

    String str1 = null;
    ByteArrayOutputStream bos = null;
    try {
        bos = new ByteArrayOutputStream();
        BufferedOutputStream dest = null;

        byte b[] = str.getBytes();
        GZIPOutputStream gz = new GZIPOutputStream(bos, b.length);
        gz.write(b, 0, b.length);
        bos.close();
        gz.close();

    } catch (Exception e) {
        System.out.println(e);
        e.printStackTrace();
    }
    byte b1[] = bos.toByteArray();
    return Base64.encode(b1);
}

My code in the .Net WebService:

    public static string compressString(string text)
{
    byte[] buffer = Encoding.UTF8.GetBytes(text);
    MemoryStream ms = new MemoryStream();
    using (GZipStream zip = new GZipStream(ms, CompressionMode.Compress, true))
    {
        zip.Write(buffer, 0, buffer.Length);
    }

    ms.Position = 0;
    MemoryStream outStream = new MemoryStream();

    byte[] compressed = new byte[ms.Length];
    ms.Read(compressed, 0, compressed.Length);

    byte[] gzBuffer = new byte[compressed.Length + 4];
    System.Buffer.BlockCopy(compressed, 0, gzBuffer, 4, compressed.Length);
    System.Buffer.BlockCopy(BitConverter.GetBytes(buffer.Length), 0, gzBuffer, 0, 4);
    return Convert.ToBase64String(gzBuffer);
}

In android:

compressString("hello"); -> "H4sIAAAAAAAAAMtIzcnJBwCGphA2BQAAAA=="

In .Net:

compressString("hello"); -> "BQAAAB+LCAAAAAAABADtvQdgHEmWJSYvbcp7f0r1StfgdKEIgGATJNiQQBDswYjN5pLsHWlHIymrKoHKZVZlXWYWQMztnbz33nvvvffee++997o7nU4n99//P1xmZAFs9s5K2smeIYCqyB8/fnwfPyLmeVlW/w+GphA2BQAAAA=="

It is interesting that when I use Decompress method in android to decompress the result of .Net compressString method, it returns the original string correctly but I get error when I decompress the result of android compressedString method.

Android Decompress method:

    public static String Decompress(String zipText) throws IOException {
    int size = 0;
    byte[] gzipBuff = Base64.decode(zipText);

    ByteArrayInputStream memstream = new ByteArrayInputStream(gzipBuff, 4,
            gzipBuff.length - 4);
    GZIPInputStream gzin = new GZIPInputStream(memstream);

    final int buffSize = 8192;
    byte[] tempBuffer = new byte[buffSize];
    ByteArrayOutputStream baos = new ByteArrayOutputStream();
    while ((size = gzin.read(tempBuffer, 0, buffSize)) != -1) {
        baos.write(tempBuffer, 0, size);
    }
    byte[] buffer = baos.toByteArray();
    baos.close();

    return new String(buffer, "UTF-8");
}

I think that there is an error in Android compressString method.
Can anybody help me?

Answer 1

According to this answer, I have 4 methods. Android and .net compress and decompress methods. These methods are compatible with each other except in one case.