Not in GZIP format problem

Question

I am experiencing the following IOException when using the GZIPInputStream:
    java.io.IOException: Not in GZIP format
        at java.util.zip.GZIPInputStream.readHeader(GZIPInputStream.java:131)
        at java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:58)
        at java.util.zip.GZIPInputStream.<init>(GZIPInputStream.java:68)
        ...I am trying to read an Entity Body from an HTTP response that has been compressed using GZIP compression. I read in chunks of 4K bytes, but my first read always ends at the Entity Body (this is not a problem of course, but I thought it was a bit odd). However, this my first read of an InputStream always gives me the following:
Status-Line
Headers
CRLF
So, the next read would return me the first byte of the Entity Body. By investigating the supplied Headers I discovered that GZIP compression is used. Therefore, I create a GZIPInputStream with the original InputStream as parameter. But when I start reading from the GZIPInputStream I get the mentioned exception.
Looking into the GZIPInputStream it seems to have a problem with the GZIP header magic number (0x8b1f). This magic number consists of two bytes. I thought it would be nice to try the following, just to see what happend:
    byte[] gzipHeader = new byte[2];
    inputStream.read(gzipHeader, 0, gzipHeader.length);
    GZIPInputStream gzipInputStream =
        new GZIPInputStream(
            new SequenceInputStream(
                new ByteArrayInputStream(gzipHeader), inputStream));
    ...And guess what? This seems to solve my problem, however I would not consider this to be a nice fix. Looking to see what is in the byte array, I discovered the following: 0x1f8b. I found the following snippet of code in GZIPInputStream:
    private int readUShort(InputStream in) throws IOException {
        int b = readUByte(in);
        return ((int)readUByte(in) << 8) | b;
    }This method is used to read in the GZIP header magic number. Now correct me if I'm wrong, but reading the bytes 0x1f8b results in the desired 0x8b1f. Therefore my little test mentioned earlier works, but why doesn't the following work:
    GZipInputStream gzipInputStream = new GZIPInputStream(inputStream);
    ....Can anybody help me with this?
Jack...

Answer 1

http://en.wikipedia.org/wiki/Gzip
Other uses
The �Content-Encoding� header in HTTP/1.1 allows clients to optionally receive compressed HTTP responses and (less commonly) to send compressed requests. The standard itself specifies two compression methods: �gzip� (RFC 1952; the content wrapped in a gzip stream) and �deflate� (RFC 1950; the content wrapped in a zlib-formatted stream). Compressed responses are supported by many HTTP client libraries, almost all modern browsers and both of the major HTTP server platforms, Apache and Microsoft IIS. Many server implementations, however, incorrectly implement the protocol by using the raw DEFLATE stream format (RFC 1951) instead. The bug is sufficiently pervasive that most modern browsers will accept both RFC 1951 and RFC 1950-formatted data for the �deflate� compressed method.