How to check if InputStream is Gzipped?

Question

Is there any way to check if InputStream has been gzipped? Here\'s the code:

public static InputStream decompressStream(InputStream input) {
    try {
               


        

Answer 1

Building on the answer by @biziclop - this version uses the GZIP_MAGIC header and additionally is safe for empty or single byte data streams.

public static InputStream maybeDecompress(InputStream input) {
    final PushbackInputStream pb = new PushbackInputStream(input, 2);

    int header = pb.read();
    if(header == -1) {
        return pb;
    }

    int b = pb.read();
    if(b == -1) {
        pb.unread(header);
        return pb;
    }

    pb.unread(new byte[]{(byte)header, (byte)b});

    header = (b << 8) | header;

    if(header == GZIPInputStream.GZIP_MAGIC) {
        return new GZIPInputStream(pb);
    } else {
        return pb;
    }
}