Sending gzipped data in WebRequest?

Question

I have a large amount of data (~100k) that my C# app is sending to my Apache server with mod_gzip installed. I'm attempting to gzip the data first using System.IO.Compression.GZipStream. PHP receives the raw gzipped data, so Apache is not uncompressing it as I would expect. Am I missing something?

System.Net.WebRequest req = WebRequest.Create(this.Url);
req.Method = this.Method; // "post"
req.Timeout = this.Timeout;
req.ContentType = "application/x-www-form-urlencoded";
req.Headers.Add("Content-Encoding: gzip");

System.IO.Stream reqStream = req.GetRequestStream();

GZipStream gz = new GZipStream(reqStream, CompressionMode.Compress);

System.IO.StreamWriter sw = new System.IO.StreamWriter(gz, Encoding.ASCII);
sw.Write( large_amount_of_data );
sw.Close();

gz.Close();
reqStream.Close()


System.Net.WebResponse resp = req.GetResponse();
// (handle response...)

I'm not entirely sure "Content-Encoding: gzip" applies to client-supplied headers.

Answer 1

According to http://www.dominoexperts.com/articles/GZip-servlet-to-gzip-your-pages

You should setContentType() to the original format, as you are doing with the application/x-www-form-urlencoded I assume. Then...

 // See if browser can handle gzip
 String encoding=req.getHeader("Accept-Encoding");
 if (encoding != null && encoding.indexOf("gzip") >=0 ) {  // gzip browser 
      res.setHeader("Content-Encoding","gzip");
      OutputStream o=res.getOutputStream();
      GZIPOutputStream gz=new GZIPOutputStream(o);
      gz.write(content.getBytes());
      gz.close();
      o.close();
            } else {  // Some old browser -> give them plain text.                        PrintWriter o = res.getWriter();
                    o.println(content);
                    o.flush();
                    o.close();
            }

Answer 2

I looked at the source code for mod_gzip and I could not find any code that decompresses data. Apparently mod_gzip only compresses outgoing data which isn't too surprising after all. The functionality you are looking for is probably rarely used, and I'm afraid you have to do your own decompression on the server.

Answer 3

Regarding your question whether Content-Encoding is applicable to client-supplied headers - according to HTTP/1.1 standard, it is:

(from section 7)

Request and Response messages MAY transfer an entity if not otherwise restricted by the request method or response status code.

(from section 7.1)

   entity-header  = Allow                    ; Section 14.7
                  | Content-Encoding         ; Section 14.11
                  | Content-Language         ; Section 14.12
                  | Content-Length           ; Section 14.13
                  | Content-Location         ; Section 14.14
                  | Content-MD5              ; Section 14.15
                  | Content-Range            ; Section 14.16
                  | Content-Type             ; Section 14.17
                  | Expires                  ; Section 14.21
                  | Last-Modified            ; Section 14.29
                  | extension-header

Answer 4

You need to change

req.Headers.Add("Content-Encoding: gzip");

to

req.Headers.Add("Content-Encoding","gzip");