Magic Wormhole: get things from one computer to another, safely

I've used this for years when passing large files between systems in weird network environments, it's almost always flawless.

For some more exotic testing, I was able to run my own magic wormhole relay[1], which let me tweak some things for faster/more reliable huge file copies. I still hate how often Google Drive will fall over when you throw a 10s-of-GB file at it.

[1] https://www.jeffgeerling.com/blog/2023/my-own-magic-wormhole...

> you need a machine that can handle whatever link speeds you need

I would have expected the relay server only being used for initial handshake to punch through NAT, after which the transfer is P2P. Only in the case of some network restrictions the data really flows through the relay. How could they afford running the free relay otherwise?

There are two servers. The "mailbox server" helps with handshakes and metadata transfers, and is super-low bandwidth, a few hundred bytes per connection. The "transit relay helper" is the one that handles the bulk data transfer iff the two sides were unable to establish a direct connection.

I've been meaning to find the time to add NAT-hole-punching for years, but haven't managed it yet. We'd use the mailbox server messages to help the two sides learn about the IP addresses to use. That would increase the percentage of transfers that avoid the relay, but the last I read, something like 20% of peer-pairs would still need the relay, because their NATs are too restrictive.

The relay usage hasn't been expensive enough to worry about, but if it gets more popular, that might change.