Update the rust toolchain version to 1.85.
Note that this is not the latest, however, it is the latest available in nixpgs,
so this version is good enough for now.
This is a breaking protocol change that prefixes all gossip messages
with their length.
This is to allow message extensions, as we'll be able to read the whole
message inclulding the extensions, without having to decode the
extensions.
It also makes it easier to check the message length before we start
decoding, so that we can reject messages that are too big.
To improve the reliability and flexibility of the protocol, we introduce
multiplexing over peer connections. This involves a new `Frame` type
that carries a stream-id and payload.
Three stream types are made available:
1. Control
2. Gossip
3. Git
This change brings the following improvements:
* Removed need to queue fetch requests
* Removed need to queue gossip messages
* Removed need for `Fetch` and `FetchOk` messages
* Service doesn't need to know about inbound fetches
* Removed one round-trip for fetch negotiation
* Removed special `done` git packet
* Removed session logic and state around Git/Fetch protocols
* Removed code around upgrading/downgrading transport
* Worker in responder mode is able to process any number of fetches
* Connections support any number of concurrent fetches
We had to introduce a few extra things however to make it all work:
* A `VarInt` type for variable-length integers, since we want the frames
to be lightweight.
* A custom "tunnel" implementation, since we couldn't use the existing
one anymore.
Overall the change removes more complexity than it adds, while improving
the protocol along the way.
Lorenz Leutgeb
Fintan Halpenny
cloudhead
Alexis Sellier