-// Download URLs
-//
-// The following "same origin" URL patterns are supported for public
-// collections (i.e., collections which can be served by keep-web
-// without making use of any credentials supplied by the client). See
-// "Same-origin URLs" below.
-//
-// http://dl.example.com/c=uuid_or_pdh/path/file.txt
-// http://dl.example.com/c=uuid_or_pdh/t=TOKEN/path/file.txt
-//
-// The following "multiple origin" URL patterns are supported for all
-// collections:
-//
-// http://uuid_or_pdh--dl.example.com/path/file.txt
-// http://uuid_or_pdh--dl.example.com/t=TOKEN/path/file.txt
-//
-// In the "multiple origin" form, the string "--" can be replaced with
-// "." with identical results (assuming the upstream proxy is
-// configured accordingly). These two are equivalent:
-//
-// http://uuid_or_pdh--dl.example.com/path/file.txt
-// http://uuid_or_pdh.dl.example.com/path/file.txt
-//
-// The first form ("uuid_or_pdh--dl.example.com") minimizes the cost
-// and effort of deploying a wildcard TLS certificate for
-// *.dl.example.com. The second form is likely to be easier to
-// configure, and more efficient to run, on an upstream proxy.
-//
-// In all of the above forms, the "dl.example.com" part can be
-// anything at all: keep-web itself ignores everything after the first
-// "." or "--". (Of course, in order for clients to connect at all,
-// DNS and any relevant proxies must be configured accordingly.)
-//
-// In all of the above forms, the "uuid_or_pdh" part can be either a
-// collection UUID or a portable data hash with the "+" character
-// optionally replaced by "-". (Replacing "+" with "-" is mandatory
-// when "uuid_or_pdh" appears in the domain name only because "+" is
-// not a valid character in a domain name.)
-//
-// In all of the above forms, a top level directory called "_" is
-// skipped. In cases where the "path/file.txt" part might start with
-// "t=" or "c=" or "_/", links should be constructed with a leading
-// "_/" to ensure the top level directory is not interpreted as a
-// token or collection ID.
-//
-// Assuming there is a collection with UUID
-// zzzzz-4zz18-znfnqtbbv4spc3w and portable data hash
-// 1f4b0bc7583c2a7f9102c395f4ffc5e3+45, the following URLs are
-// interchangeable:
-//
-// http://zzzzz-4zz18-znfnqtbbv4spc3w.dl.example.com/foo/bar.txt
-// http://zzzzz-4zz18-znfnqtbbv4spc3w.dl.example.com/_/foo/bar.txt
-// http://zzzzz-4zz18-znfnqtbbv4spc3w--dl.example.com/_/foo/bar.txt
-// http://1f4b0bc7583c2a7f9102c395f4ffc5e3-45--foo.example.com/foo/bar.txt
-// http://1f4b0bc7583c2a7f9102c395f4ffc5e3-45--.invalid/foo/bar.txt
-//
-// An additional form is supported specifically to make it more
-// convenient to maintain support for existing Workbench download
-// links:
-//
-// http://dl.example.com/collections/download/uuid_or_pdh/TOKEN/foo/bar.txt
-//
-// A regular Workbench "download" link is also accepted, but
-// credentials passed via cookie, header, etc. are ignored. Only
-// public data can be served this way:
-//
-// http://dl.example.com/collections/uuid_or_pdh/foo/bar.txt