Sending gzipped form data

Question

I've heard how browsers can receive gzipped pages from the server. Can they also gzip form data that they send to the server? And if it's possible, how would I decompress this data on the server?

I'm using AppEngine's webapp module, but a general explanation / pointers to tutorials would be sufficient. I've done some googling to no avail.

Answer 1

Short answer:

No, most browsers will not compress form data for client requests.

Long answer:

Yes, all browsers allow the client to send compressed form data. But since the browsers wouldn't compress the data for us, we've got to compress it ourselves.

Gzip uses the DEFLATE algorithm, which is publicly available and free to use. What can be done is to compress the form data on the client-side using JavaScript (download a JS Gzip library if you don't want to write one yourself), then send the compressed data to the server through either GET, POST, or PUT using XMLHttpRequest.

If you are in control of your web server, you could simply grab the data and uncompress it. If you are not in control, you will have to follow whatever policies set in place. For example, some web servers may require you to set a specific Content-Type, while others may not support it at all.

Lastly note that if your resource is a file that is already compressed, there may be no advantages in gzipping it. However if your resource is huge uncompressed data (e.g. a forum post of 80000 characters), the advantages are enormous.

Answer 2

I think that browsers probably can send gzipped form data to the server. I don't know if it is common to do so or not.

The sender would need to make sure to have a Content-Encoding: header with a value that included gzip. The body of the message would then need to be encoded with a gzip encoding, and one can compress / decompress gzipped data in python with the gzip.GzipFile class. I don't know if the gzip module is available on appengine -- if it requires a C-module implementation, then it probably wouldn't be (not sure if it does).

As far as the decoding goes, it's possible that the web machinery that runs before your app-engine program gets any input will decode gzipped content. I've done almost no work with appengine, so I'm not familiar with that sort of detail. It's possible though, that you just don't have to worry about it on the server end...it just gets taken care of automatically. You'd have to check.

It might be useful to look at RFC2616, especially the sections for Accept-Encoding and Content-Encoding.

Answer 3

Short answer: No.

See: Why can't browser send gzip request?