ActivityPub => ATProto: handle usernames with _ and ~ chars

[snarfed]

This is a fun one. First user with an underscore in their username signed up just now, https://me.dm/@punkscience_ns , @punkscience. (Hi Darryl! Sorry for the trouble!)

We translated the fediverse address @punkscience_ns@me.dm to the bridged Bluesky handle punkscience_ns.me.dm.ap.brid.gy and created the DNS TXT record _atproto.punkscience_ns.me.dm.ap.brid.gy, which is serving fine. PLC directory has it in https://web.plc.directory/did/did:plc:di27vbfe6wutukod4g36kovz.

However, ATProto handles don't allow the underscore character. 🤦 (Also see swicg/activitypub-webfinger#9) So, I guess we need to translate underscores to maybe dashes, and hope we don't hit a collision between eg x_y and x-y on the same instance.

[snarfed]

Also need to handle tildes (~). Probably even less common, but theoretically possible.

Related: #744, #830

[snarfed]

Got another one: https://mastodon.social/users/_dmh, did:plc:desdlx43ak66lzgakb5tvyss, @dmhowcroft. (Sorry Dave!)

[dmhowcroft]

Thanks! Looking forward to seeing it resolved :)

[snarfed]

And:

• https://darmstadt.social/users/ceol_agus_ol, did:plc:xry5u23qftlcaysecxbhuv4m
• https://tomkahe.com/users/daily_wikipedia, did:plc:ujtdubiivqcqb2uvygsr4cne
• https://mastodon.social/users/carb_uncle, did:plc:oegzpinpvkhf5sv5oj4f7mq7
• https://mastodon.world/users/edwin_cikan, did:plc:ujyugmm5ko3l6aq6wbz24y2g
• https://mastodon.gamedev.place/users/_DenisProdan_, did:plc:rf3twh7j5mp7nfmlctvoummd
• https://warpday.net/users/98ftq556kb, @hirata_@warpday.net, did:plc:wqcmjyeohwcthpjuiorilwwc

[snarfed]

Implemented and deployed. Next, fixing these users ^ manually.

[snarfed]

Woo, first profile I've seen this work on! https://wetdry.world/@mary_ext => https://bsky.app/profile/mary-ext.wetdry.world.ap.brid.gy

[qazmlp]

What happens now if there's a collision? Is the second user not bridged or do they just not get a friendly handle?

[snarfed]

They're not bridged.

I honestly couldn't predict if we hit that collision in a week, or a quarter, or five years, or never. I suspect closer to five years. We'll cross that bridge when we come to it.

[snarfed]

Need to do a bit more here: ATProto handles can't begin or end with -. https://mastodon.gamedev.place/users/_DenisProdan_ and https://warpday.net/users/98ftq556kb (@hirata_@warpday.net) failed this.

[dmhowcroft]

Is my underscore-initial username bridged to ATP now?

[snarfed]

@dmhowcroft sadly no, sorry, and honestly I don't yet have a plan for how to support usernames that begin or end with underscores or dashes.

[snarfed]

OK, I think we're set here. _ and ~ are converted to - except if they're at the beginning or end, where they're not supported, and that's now documented. I've filed #1005 for that.