HostedFiles: need url for viewing file content online

In Launchpad, you can access a file attachment via a launchpad librarian URL. For instance:

  http://launchpadlibrarian.net/30939908/BootDmesg.txt

However, from the bug object itself, it doesn't appear possible to determine this URL. Here's the info I can access:

title: BootDmesg.txt
subject: Re: xorg eats up all my CPU
filename: BootDmesg.txt
owner: Nicolò Chieffo
created: 2009-08-28 15:38:32.527415+00:00
modified: Fri, 28 Aug 2009 16:38:32 GMT
ispatch: Unspecified
http_etag: "d885865de3b9064125e67063e1eb99a8d20c026b"
content-type: text/plain; charset="utf-8"
a.url: https://api.edge.launchpad.net/beta/bugs/420600/+attachment/686514
fb.url: https://api.edge.launchpad.net/beta/bugs/420600/+attachment/686514/data
data.params: []
data.wadl: <wadllib.application.Resource object at 0x30e0dd0>
isatty: False
len: 53176
mode: r
pos: 0
softspace: 0

Most notably, the fb.url object seems to not work, even if I try permutations such as:

  https://bugs.edge.launchpad.net/bugs/420600/+attachment/686514/data

It would be helpful either to have a way to determine the launchpadlibrarian.net url, or for the filebuffer url attribute to point to something that can be viewed in the web browser.