Send client version with bind message

[wuan]

This PR sets the client_version field in the bind message (see magic-wormhole/magic-wormhole/src/wormhole_rendezvous.py:182). So far this is only being used by the Python and Wormhole-William (Go) clients.

It will use the following mapping:

implementation	rust
version	<package-version>

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (46eceb0) 43.73% compared to head (00842fb) 43.74%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #176      +/-   ##
==========================================
+ Coverage   43.73%   43.74%   +0.01%     
==========================================
  Files          18       18              
  Lines        2552     2558       +6     
==========================================
+ Hits         1116     1119       +3     
- Misses       1436     1439       +3     

Impacted Files	Coverage Δ
src/core.rs	78.91% <100.00%> (+0.38%)	⬆️
src/core/server_messages.rs	68.57% <100.00%> (+0.92%)	⬆️

... and 3 files with indirect coverage changes

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[piegamesde]

This field does not seem to be specified in the protocols. We should fix that

[piegamesde]

Using lifetimes here has the effect of avoiding about two allocations in total and is total overkill. But if you really want to have a borrowed version of the struct, then use Cow instead please.

[wuan]

I'm new to Rust and need to find out how to avoid lifetimes then. Should I prefer to use String instead of &str to achieve that?

[piegamesde]

Just clone liberally. And if you find yourself cloning too much, wrap in a reference counter to make it cheaper.

One of the key lessons most beginners eventually learn is that Rust gives you the possibility to be efficient, but it's not always necessary/productive to make use of that. (Incidentally, I think this is also where a lot of the "fighting the borrow checker" meme comes from)

[wuan]

The solution is now hopefully clean enough.

[piegamesde]

Yes, it is.

Unless this PR is urgent, I'd like to discuss the client-version field in the protocol before merging this. Depending on what the values mean, I'd personally prefer CLIENT_NAME = "wormhole-rs"; over "rust". On the other hand, there may exist multiple clients using this library, should the value reflect that or not?

[wuan]

On the other hand, there may exist multiple clients using this library, should the value reflect that or not?

That would be a future update to enable overriding this information by the caller, like in https://github.com/psanford/wormhole-william/blob/master/rendezvous/options.go.

[piegamesde]

magic-wormhole/magic-wormhole-protocols#35