NSURLConnection gzip magic

For quite some time I ranted about not being able to use compressed network communcation out-of-the-box on the iPhone.

Despite being undocumented (or I just overlooked the hint), NSURLConnection does gzip decompression transparently!

That’s how to use it:

1. ensure the webserver sends gzipped content, use e.g. wget to verify:

   $ wget –header=‘Accept-Encoding: gzip’ 
   
       –server-response http://example.com/demo.xmlz
   

   It should (in case of a gzipped xml document) look like

   HTTP/1.1 200 OK
   …
   Content-Type: text/xml
   Content-Encoding: gzip
   …
   

2. If your webserver doesn’t support transparent compression, you can still upload gzipped content and tell the server to send the correct response headers by setting up a .htaccess file:

   ...
   AddType text/xml .xml .xmlz
   AddEncoding gzip .gz .xmlz
   
   # inspired by
   # http://betterexplained.com/articles/
   #  how-to-optimize-your-site-with-gzip-compression/
   # compress all text & html:
   AddOutputFilterByType DEFLATE text/html text/plain text/xml
   ...
   

3. to verify from within your app, log the response header in the NSURLConnection callbacks:

   - (void)connection:(NSURLConnection *)connection
     didReceiveResponse:(NSURLResponse )response
   {
       NSLog(@“didReceiveResponse %@: %@“, [response URL],
   [(NSHTTPURLResponse)response allHeaderFields]);
       buffer = [[NSMutableData dataWithCapacity:1024*1024] retain];
   }
   
   
   
   (void)connection:(NSURLConnection *)connection
   didReceiveData:(NSData *)dat
   {
   [buffer appendData:dat];
   }
   
   (void)connectionDidFinishLoading:(NSURLConnection *)connection
   {
   NSLog(@“connectionDidFinishLoading %d bytes”, [buffer length]);
   [buffer release];
   }
   

It should look like

2009-06-28 14:31:09.722 DemoApp[3981:20b] \
  didReceiveResponse http://example.com/demo.xmlz: {
...
"Content-Type" = "text/xml";
"Content-Encoding" = gzip;
"Content-Length" = 123042;
}
...
2009-06-28 14:31:11.619 DemoApp[3981:20b] \
  connectionDidFinishLoading 602979 bytes

As you can see we received way more bytes than went over the wire.

• enjoy lightning fast network communication!

P.S.: It seems not to be necessary setting the request header yourself:

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url
    cachePolicy:NSURLRequestReloadIgnoringLocalCacheData
    timeoutInterval:60.0];
// set explicitly:
[request setValue:@"gzip" forHTTPHeaderField:@"Accept-Encoding"];