[tahoe-dev] [tahoe-lafs] #827: Support forcing download using "Content-Disposition: attachment" in WUItre

tahoe-lafs trac at allmydata.org
Sun Nov 1 06:34:45 UTC 2009

#827: Support forcing download using "Content-Disposition: attachment" in WUItre
 Reporter:  davidsarah          |           Owner:  nobody   
     Type:  defect              |          Status:  new      
 Priority:  major               |       Milestone:  undecided
Component:  unknown             |         Version:  1.5.0    
 Keywords:  security usability  |   Launchpad_bug:           
 Typical behaviour of web browsers for a retrieved over HTTP[S], is to
 decide based on its inferred MIME type whether to display it, pass it to
 some plugin/helper app, or treat it as a download (either pass it to a
 download manager or prompt the user to save it locally). The inferred MIME
 type is arrived at by rules that '''no-one''' understands; the HTTP spec
 says that the HTTP Content-Type takes precedence, but browsers
 deliberately violate that in some cases, and the result can even vary
 nondeterministically depending on network delays.

 Sometimes it's useful to override this behaviour and force the browser to
 treat the file as a download, regardless of its inferred MIME type. This
 can be done using the Content-Disposition HTTP header, e.g. "Content-
 Disposition: attachment; filename=suggested_name".

 (Well, not actually force, but strongly hint. I think all the common
 browsers now implement this; IE has had some bugs
 http://support.microsoft.com/kb/279667 but I think they are all pre-IE6.)

 Content-Disposition is specified in:
  * http://www.w3.org/Protocols/rfc2616/rfc2616-sec19.html#sec19.5.1
  * http://tools.ietf.org/html/draft-reschke-rfc2183-in-http-00

 (The "very serious security considerations" mentioned in
 http://www.w3.org/Protocols/rfc2616/rfc2616-sec15.html#sec15.5 are
 scaremongering. A server can't do anything with {{{Content-Disposition:
 attachment}}} that can't also be done via the MIME type.)

 To close this ticket,
  * add an optional parameter to the webapi that will force a download.
  * modify Tahoe directory listings to include 'download' and 'view' links.

 Note that if the most prominant link for a non-directory file was the
 download link, that would allow the WUI to be used from a browser (with
 some care on the part of users) without necessarily being vulnerable to
 the same-origin attacks described in #615. Users would only be vulnerable
 to these attacks if they click the view link, or if they view the
 downloaded local files in a browser that treats all file URLs as same-
 origin (or has some other related bug such as
 http://www.mozilla.org/security/announce/2009/mfsa2009-30.html ).

Ticket URL: <http://allmydata.org/trac/tahoe/ticket/827>
tahoe-lafs <http://allmydata.org>
secure decentralized file storage grid

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