Expand shortened URLs?

[charmander]

Sometimes people end up putting shortened URLs places; sometimes it’s by accident. We should consider undoing this, since it’s unnecessary tracking, latency, phishing risk, unsearchability, and plenty more bad stuff.

• t.co
• bit.ly
• ⋮

I think fully expanding user links, but preserving the shortened link text while rewriting the link target for Markdown, makes sense.

Proposed implementation:

• new table link_expansions (shortened text PRIMARY KEY, destination text, created timestamptz NOT NULL DEFAULT now(), fetched timestamptz) where shortened is normalized (no protocol or irrelevant querystring)
• insert when editing user links or Markdown
• background process to fill destination IS NULL rows by least recently fetched (nulls first) and least recently created
• query (cache_multi_on_arguments with should_cache non-null and non-shortened; recursive) when rendering user links or Markdown, falling back to original link when not successfully fetched yet
• rendering can also remove redirects like google.com/url