eth: implement eth66 (ethereum#22241)

* eth/protocols/eth: split up the eth protocol handlers

* eth/protocols/eth: define eth-66 protocol messages

* eth/protocols/eth: poc implement getblockheaders on eth/66

* eth/protocols/eth: implement remaining eth-66 handlers

* eth/protocols: define handler map for eth 66

* eth/downloader: use protocol constants from eth package

* eth/protocols/eth: add ETH66 capability

* eth/downloader: tests for eth66

* eth/downloader: fix error in tests

* eth/protocols/eth: use eth66 for outgoing requests

* eth/protocols/eth: remove unused error type

* eth/protocols/eth: define protocol length

* eth/protocols/eth: fix pooled tx over eth66

* protocols/eth/handlers: revert behavioural change which caused tests to fail

* eth/downloader: fix failing test

* eth/protocols/eth: add testcases + fix flaw with header requests

* eth/protocols: change comments

* eth/protocols/eth: review fixes + fixed flaw in RequestOneHeader

* eth/protocols: documentation

* eth/protocols/eth: review concerns about types

eth/downloader/peer.go

@@ -29,6 +29,7 @@ import (
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/eth/protocols/eth"
 	"github.com/ethereum/go-ethereum/event"
 	"github.com/ethereum/go-ethereum/log"
 )
@@ -457,7 +458,7 @@ func (ps *peerSet) HeaderIdlePeers() ([]*peerConnection, int) {
 		defer p.lock.RUnlock()
 		return p.headerThroughput
 	}
-	return ps.idlePeers(64, 65, idle, throughput)
+	return ps.idlePeers(eth.ETH64, eth.ETH66, idle, throughput)
 }
 
 // BodyIdlePeers retrieves a flat list of all the currently body-idle peers within
@@ -471,7 +472,7 @@ func (ps *peerSet) BodyIdlePeers() ([]*peerConnection, int) {
 		defer p.lock.RUnlock()
 		return p.blockThroughput
 	}
-	return ps.idlePeers(64, 65, idle, throughput)
+	return ps.idlePeers(eth.ETH64, eth.ETH66, idle, throughput)
 }
 
 // ReceiptIdlePeers retrieves a flat list of all the currently receipt-idle peers
@@ -485,7 +486,7 @@ func (ps *peerSet) ReceiptIdlePeers() ([]*peerConnection, int) {
 		defer p.lock.RUnlock()
 		return p.receiptThroughput
 	}
-	return ps.idlePeers(64, 65, idle, throughput)
+	return ps.idlePeers(eth.ETH64, eth.ETH66, idle, throughput)
 }
 
 // NodeDataIdlePeers retrieves a flat list of all the currently node-data-idle
@@ -499,7 +500,7 @@ func (ps *peerSet) NodeDataIdlePeers() ([]*peerConnection, int) {
 		defer p.lock.RUnlock()
 		return p.stateThroughput
 	}
-	return ps.idlePeers(64, 65, idle, throughput)
+	return ps.idlePeers(eth.ETH64, eth.ETH66, idle, throughput)
 }
 
 // idlePeers retrieves a flat list of all currently idle peers satisfying the