Created networking flow (markdown)

networking-flow.md

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+This is a collection of notes following networking related code in a beacon_node instance using the Nim libp2p implementation on Linux.
+
+beacon_chain/beacon_node.nim:
+
+- BeaconNode.start() waitsFor node.connectToNetwork()
+- BeaconNode.connectToNetwork() awaits node.network.connectToNetwork(node.bootstrapNodes, node.bootstrapEnrs)
+
+beacon_chain/eth2_network.nim:
+
+- Eth2Node.connectToNetwork(seq[ENode], seq[enr.Record])
+  - for each bootstrap ENR, calls Eth2Node.addKnownPeer()
+  - awaits Eth2Node.start()
+
+beacon_chain/libp2p_backend.nim:
+
+- Eth2Node.start()
+  - calls Eth2DiscoveryProtocol.open()
+  - calls Eth2DiscoveryProtocol.start()
+  - awaits Switch.start() and stores the resulting seq[Future[void]] in Eth2Node.libp2pTransportLoops; nothing further is done with those futures
+  - tracesAsyncErrors Eth2Node.runDiscoveryLoop()
+
+vendor/nim-libp2p/libp2p/switch.nim:
+
+- Switch.start()
+  - for each Switch.transports and each Switch.peerInfo awaits Transport.listen(MultiAddress, inner `handle` closure)
+  - returns a seq of these futures
+
+- Switch.start.handle(Connection)
+  - awaits Switch.upgradeIncoming(Connection)
+  - awaits Connection.close()
+  - awaits Switch.cleanupConn(Connection)