How can I Zip and Unzip a string using GZIPOutputStream that is compatible with .Net?

Question

I need an example for compressing a string using GZip in android. I want to send a string like "hello" to the method and get the following zipped string:

BQAAAB+LCAAAAAAABADtvQdgHEmWJSYvbcp7f0r1StfgdKEIgGATJNiQQBDswYjN5pLsHWlHIymrKoHKZVZlXWYWQMztnbz33nvvvffee++997o7nU4n99//P1xmZAFs9s5K2smeIYCqyB8/fnwfPyLmeVlW/w+GphA2BQAAAA==

Then I need to decompress it. Can anybody give me an example and complete the following methods?

private String compressString(String input) {
    //...
}

private String decompressString(String input) {
    //...
}

Thanks,

---

update

According to scessor's answer, Now I have the following 4 methods. Android and .net compress and decompress methods. These methods are compatible with each other except in one case. I mean they are compatible in the first 3 states but incompatible in the 4th state:

• state 1) Android.compress <-> Android.decompress: (OK)
• state 2) Net.compress <-> Net.decompress: (OK)
• state 3) Net.compress -> Android.decompress: (OK)
• state 4) Android.compress -> .Net.decompress: (NOT OK)

can anybody solve it?

Android methods:

public static String compress(String str) throws IOException {

    byte[] blockcopy = ByteBuffer
            .allocate(4)
            .order(java.nio.ByteOrder.LITTLE_ENDIAN)
            .putInt(str.length())
            .array();
    ByteArrayOutputStream os = new ByteArrayOutputStream(str.length());
    GZIPOutputStream gos = new GZIPOutputStream(os);
    gos.write(str.getBytes());
    gos.close();
    os.close();
    byte[] compressed = new byte[4 + os.toByteArray().length];
    System.arraycopy(blockcopy, 0, compressed, 0, 4);
    System.arraycopy(os.toByteArray(), 0, compressed, 4,
            os.toByteArray().length);
    return Base64.encode(compressed);

}

public static String decompress(String zipText) throws IOException {
    byte[] compressed = Base64.decode(zipText);
    if (compressed.length > 4)
    {
        GZIPInputStream gzipInputStream = new GZIPInputStream(
                new ByteArrayInputStream(compressed, 4,
                        compressed.length - 4));

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        for (int value = 0; value != -1;) {
            value = gzipInputStream.read();
            if (value != -1) {
                baos.write(value);
            }
        }
        gzipInputStream.close();
        baos.close();
        String sReturn = new String(baos.toByteArray(), "UTF-8");
        return sReturn;
    }
    else
    {
        return "";
    }
}

.Net methods:

public static string compress(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);
}

public static string decompress(string compressedText)
{
    byte[] gzBuffer = Convert.FromBase64String(compressedText);
    using (MemoryStream ms = new MemoryStream())
    {
        int msgLength = BitConverter.ToInt32(gzBuffer, 0);
        ms.Write(gzBuffer, 4, gzBuffer.Length - 4);

        byte[] buffer = new byte[msgLength];

        ms.Position = 0;
        using (GZipStream zip = new GZipStream(ms, CompressionMode.Decompress))
        {
            zip.Read(buffer, 0, buffer.Length);
        }

        return Encoding.UTF8.GetString(buffer);
    }
}

Answer 1

The GZIP methods:

public static byte[] compress(String string) throws IOException {
    ByteArrayOutputStream os = new ByteArrayOutputStream(string.length());
    GZIPOutputStream gos = new GZIPOutputStream(os);
    gos.write(string.getBytes());
    gos.close();
    byte[] compressed = os.toByteArray();
    os.close();
    return compressed;
}

public static String decompress(byte[] compressed) throws IOException {
    final int BUFFER_SIZE = 32;
    ByteArrayInputStream is = new ByteArrayInputStream(compressed);
    GZIPInputStream gis = new GZIPInputStream(is, BUFFER_SIZE);
    StringBuilder string = new StringBuilder();
    byte[] data = new byte[BUFFER_SIZE];
    int bytesRead;
    while ((bytesRead = gis.read(data)) != -1) {
        string.append(new String(data, 0, bytesRead));
    }
    gis.close();
    is.close();
    return string.toString();
}

And a test:

final String text = "hello";
try {
    byte[] compressed = compress(text);
    for (byte character : compressed) {
        Log.d("test", String.valueOf(character));
    }
    String decompressed = decompress(compressed);
    Log.d("test", decompressed);
} catch (IOException e) {
    e.printStackTrace();
}

=== Update ===

If you need .Net compability my code has to be changed a little:

public static byte[] compress(String string) throws IOException {
    byte[] blockcopy = ByteBuffer
        .allocate(4)
        .order(java.nio.ByteOrder.LITTLE_ENDIAN)
        .putInt(string.length())
        .array();
    ByteArrayOutputStream os = new ByteArrayOutputStream(string.length());
    GZIPOutputStream gos = new GZIPOutputStream(os);
    gos.write(string.getBytes());
    gos.close();
    os.close();
    byte[] compressed = new byte[4 + os.toByteArray().length];
    System.arraycopy(blockcopy, 0, compressed, 0, 4);
    System.arraycopy(os.toByteArray(), 0, compressed, 4, os.toByteArray().length);
    return compressed;
}

public static String decompress(byte[] compressed) throws IOException {
    final int BUFFER_SIZE = 32;
    ByteArrayInputStream is = new ByteArrayInputStream(compressed, 4, compressed.length - 4);
    GZIPInputStream gis = new GZIPInputStream(is, BUFFER_SIZE);
    StringBuilder string = new StringBuilder();
    byte[] data = new byte[BUFFER_SIZE];
    int bytesRead;
    while ((bytesRead = gis.read(data)) != -1) {
        string.append(new String(data, 0, bytesRead));
    }
    gis.close();
    is.close();
    return string.toString();
}

You can use the same test script.