Recipe about gossiping with other nodes over the network

[JoshOrndorff]

[nuke-web3]

Hi, I have few question regarding gossip. I try to use sc_network_gossip::GossipEngine. I hope this is the right way to go.
Do we get the messages sent to us using Receiver returned by messages_for? How does this relate to the ImportQueue in case of gossiping blocks, though I would like to transmit other messages, too)? If I register a message with register_gossip_message and send it selectively to a single peer (using send_topic), does only the recipient receive it or other connected peers, too, after they poll the receiver of messages_for? How do I receive messages sent by send_message, where no topic is specified? Thank you.

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I'd recommend to directly use the NetworkService in sc_network instead. It's more simple to use
Step 1: add an entry in NetworkConfiguration::extra_sets: https://docs.rs/sc-network/0.9.0/sc_network/config/struct.NetworkConfiguration.html#structfield.extra_sets
See example config for what we use for GrandPa: https://github.com/paritytech/substrate/blob/6ac86d545f6da8e4afc373dc0876c3e7ba79e51b/client/finality-grandpa/src/lib.rs#L690-L700
Step 2: call events_stream at initialization: https://docs.rs/sc-network/0.9.0/sc_network/struct.NetworkService.html#method.event_stream
Step 3: if you want to gossip to the same peers you're connected to for syncing (which is the easy option), call add_set_reserved and remove_set_reserved when you receive SyncConnected and SyncDisconnected (example)
Adding/removing reserved peers sets the list of peers to have an open gossiping channel with
Step 4: you will receive events whenever a gossiping channel is open or closed or a message received (https://docs.rs/sc-network/0.9.0/sc_network/enum.Event.html)
Step 5: use write_notification to send a message to someone: https://docs.rs/sc-network/0.9.0/sc_network/struct.NetworkService.html#method.write_notification
Step 7: profit