How best to think of protocols

[dadepo]

While going through the source, I found the list of protocols here

I am a bit confused on how to think about protocols semantically in rust-libp2p as I see things that represents different things conceptually. For example in the directory there is kad and mdns, which I believe are peer discovery mechanism. Also there is ping and identify which I believe has nothing to do with discovery but are closer to the definition of what a protocol should be. Also there is floodsub and gossipsub which appears to be conceptually different also.

So what exactly are protocols in rust-libp2p? What is the best way to think about them conceptually?

[thomaseizinger]

I think the Wikipedia definition is pretty good here:

A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchronization of communication and possible error recovery methods.

There are also specifications for the libp2p protocols.

In a nutshell, you can think of every communication that can be defined in an isolated fashion as a protocol. On this level, kad, mdns, ping, identify, gossipsub are all protocols. They may allow you to achieve different goals, like peer discovery, metadata exchange or messaging but fundamentally, they are all protocols. In fact, every communication between two pieces of software IS a protocol. Often times, it is just not as explicitly specified.

[mxinden]

The mental model I use:

/transports contains transport protocols, enabling one to exchange bytes between two endpoints only.
/protocols contains peer-to-peer protocols, building on top of some mechanism to exchange bytes between two endpoints, orchestrating these connections to build something bigger beyond two peers.

Does that help?