Re: [Ksummit-discuss] Fwd: [TECH TOPIC] QR encoded oops for the kernel

[josh@joshtriplett.org]

On Tue, May 13, 2014 at 05:52:07PM +0200, Levente Kurusa wrote:
> Hi,
> 
> On Tue, May 13, 2014 at 12:08:51AM -0700, Josh Triplett wrote:
> > On Tue, May 13, 2014 at 09:44:26AM +0300, Teodora Băluţă wrote:
> > > On Mon, May 12, 2014 at 7:15 PM, Jason Cooper <jason@lakedaemon.net> wrote:
> > > > I'd like the URL to be valid (meaning base64 the compressed data) so
> > > > that we can get the data to the kernel.org server as easily as possible.
> > > > Making the app a requirement for reporting is too onerous for
> > > > non-developers.  I see no reason we can't link to (Open in/Install) it
> > > > on the webform though.
> > > 
> > > So from what I can understand, the QR code has an URL that has the
> > > base64 of the compressed Oops message. Right? I see three problems
> > > with this approach:
> > > 
> > > - base64 adds about 33% overhead (it's turning 3 octets into 4 encoded
> > > characters + padding). One issue with QR codes is that they have a
> > > limited amount of characters they can hold so that's why I do the
> > > compression in the first place
> > 
> > Putting base64-encoded data in a URL in a binary-format QR code with 8
> > bits per character does indeed waste quite a bit of space.  However, you
> > could put base32-encoded data into an alphanumeric-formatted QR code
> > with 5.5 bits per character, which would waste very little space.  (Or,
> > more efficiently but less conveniently, base40 or so.)
> 
> Base32 does sound good until you realize that it requires roughly 20%
> more space than Base64 does. We would need some calculations to
> decide if we were to go down this path.

QR has several encoding modes; it doesn't matter that base32 uses more
space in terms of characters, because QR itself has an alphanumeric
encoding mode that only uses 5.5 bits per character to encode 45
possible alphanumeric/symbol characters.  base64 wastes far more
relative to bytes (6 versus 8 bits) than base32 wastes relative to QR
alphanumeric (5 versus 5.5 bits).

- Josh Triplett