Fate of registerProtocolHandler() / registerContentHandler() and friends?

[annevk]

See also #198.

Both of these methods are rather poorly implemented. Are they used to the extent that we need to keep them? Should they be improved?

[domenic]

I use them on every new computer for mailto: (Inbox/Gmail) and irc:/ircs: (IRCCloud), in both Chrome and Firefox. I don't really understand what the problem is.

[annevk]

Is registerContentHandler() implemented? Are the remaining four methods? Are they supported as part of Fetch or navigate? (Last I checked not consistent across implementations.)

I think you're correct though that at least registerProtocolHandler() has its use.

[jscinoz]

If we were to specify that these are supported as part of Fetch (in addition to navigation), and as a result, could be handled by service workers, I can think of at least a few use cases that wouldn't otherwise be possible:

• Service worker protocol handlers - e.g: implement a SW that handles magnet: URIs and uses feross/webtorrent to retrieve content, without the caller needing any understanding of BitTorrent specifics.
• Service worker content handlers - e.g: implement a SW that handles image/bpg and can transparently convert to image/png in browsers lacking native support.

There would, of course, need to be some thought & discussion around the security & permissions model for this

[joshtriplett]

I'm strongly interested in continued availability of registerProtocolHandler.

[annevk]

For Live DOM Viewer:

<script>
["registerProtocolHandler",
 "registerContentHandler",
 "isProtocolHandlerRegistered",
 "isContentHandlerRegistered",
 "unregisterProtocolHandler",
 "unregisterContentHandler"].forEach(val => {
  w(navigator[val] !== undefined)
})
</script>

Edge and Safari support none of them.

Firefox supports registerProtocolHandler and registerContentHandler (and the latter only for a select set of RSS-related MIME types). Chrome supports registerProtocolHandler and unregisterProtocolHandler.

I'm happy to wait a little longer with registerProtocolHandler and maybe unregisterProtocolHandler, but the rest should really be removed at this point. Will work on a PR.