Question

I have a web site in asp.NET 4 (C#).

I’m trying to find a way to better optimize bandwidth for my website.

I read many articles saying that DEFLATE is faster and smaller that GZIP because GZIP (based on DEFLATE) adds some extra data.

Checking the headers of bing.com and google.com it seems that they both send GZIP-encoded data.

Assuming what I read is true, I miss the advantage of GZIP in this case. So I suspect there should be a good reason to prefer GZIP to DEFLATE.

My questions:

• Does GZIP offer any advantage over DEFLATE I’m not aware of?
• Any clue why major search engines use GZIP?

Here’s the code I’m using to send DEFLATE (from Global.asax):

protected void Application_PreRequestHandlerExecute(object sender, EventArgs e)
    {

        HttpApplication app = sender as HttpApplication;
        string acceptEncoding = app.Request.Headers["Accept-Encoding"];
        Stream prevUncompressedStream = app.Response.Filter;

        if (!(app.Context.CurrentHandler is Page ||
            app.Context.CurrentHandler.GetType().Name == "SyncSessionlessHandler") ||
            app.Request["HTTP_X_MICROSOFTAJAX"] != null)
            return;

        if (acceptEncoding == null || acceptEncoding.Length == 0)
            return;

        acceptEncoding = acceptEncoding.ToLower();

        if (acceptEncoding.Contains("deflate") || acceptEncoding == "*")
        {
            // defalte
            app.Response.Filter = new DeflateStream(prevUncompressedStream,
                CompressionMode.Compress);
            app.Response.AppendHeader("Content-Encoding", "deflate");
        }
        else if (acceptEncoding.Contains("gzip"))
        {
            // gzip
            app.Response.Filter = new GZipStream(prevUncompressedStream,
                CompressionMode.Compress);
            app.Response.AppendHeader("Content-Encoding", "gzip");
        }
    }

Answer 1

Gzip is the more reliable because it is deflate plus a few headers and a check sum. In other words gzip is deflate, and extra headers and check sum. Deflate is checked with adler32, which is also part of gzip. Because the gzip payload is a DEFLATE-compressed payload.

Deflate info

Gzip info

a gzip file/stream contains:

- a 10-byte header, containing a magic number, a version number and a time stamp
- optional extra headers, such as the original file name,
- a body, containing a DEFLATE-compressed payload
- an 8-byte footer, containing a CRC-32 checksum and the length of the original uncompressed data