add support for custom protocol matching function

[richard-ramos]

This allows setting a custom protocol matching function.

fullTextMatch := func(expectedProtocol string) func(string) bool {
    return func(protocolToVerify string) bool {
	return protocolToVerify == expectedProtocol
    }
}

// create a new PubSub service using the GossipSub router
ps, err := pubsub.NewGossipSub(ctx, h, pubsub.WithProtocolMatchFunction(fullTextMatch))

Could potentially be used to allow semver matching

protoMinor := protocol.ID("/testing/1.2.0")
mfunc, err := helpers.MultistreamSemverMatcher(protoMinor)
if err != nil {
    t.Fatal(err)
}
ps, err := pubsub.NewGossipSub(ctx, h, 
     pubsub.WithProtocolMatchFunction(mfunc),
     pubsub.WithGossipSubProtocols([]protocol.ID{pubsub.GossipSubID_v11, pubsub.GossipSubID_v10, pubsub.FloodSubID, protoMinor}, pubsub.GossipSubDefaultFeatures)
)

[vyzo]

Thank you, this looks useful.

A couple of small changes are needed:

• It should probably be combined with the appropriate feature test function in gossipsub.
  Mind adding some about this in the documentation?
• No need to use a pointer! functions can be tested against nil with !=

[vyzo]

Also, can you add a test?

[vyzo]

thank you, this is looking good. Just a couple of minor things to fix and we can merge.

[vyzo]

we don't need to initialize this, the default is fine.

[vyzo]

Note that we do it for signKey to be explicit about it, as these are grouped together.

[vyzo]

I would say here "Should be combined ... for checking if certain protocol features are supported"

[richard-ramos]

I finished the required changes. Thank you for the code review!

[vyzo]

thank you!