p2p accounting (#17951)

* p2p/protocols: introduced protocol accounting

* p2p/protocols: added TestExchange simulation

* p2p/protocols: add accounting simulation

* p2p/protocols: remove unnecessary tests

* p2p/protocols: comments for accounting simulation

* p2p/protocols: addressed PR comments

* p2p/protocols: finalized accounting implementation

* p2p/protocols: removed unused code

* p2p/protocols: addressed @nonsense PR comments

p2p/protocols/accounting.go

@@ -0,0 +1,172 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package protocols
+
+import "github.com/ethereum/go-ethereum/metrics"
+
+//define some metrics
+var (
+	//NOTE: these metrics just define the interfaces and are currently *NOT persisted* over sessions
+	//All metrics are cumulative
+
+	//total amount of units credited
+	mBalanceCredit = metrics.NewRegisteredCounterForced("account.balance.credit", nil)
+	//total amount of units debited
+	mBalanceDebit = metrics.NewRegisteredCounterForced("account.balance.debit", nil)
+	//total amount of bytes credited
+	mBytesCredit = metrics.NewRegisteredCounterForced("account.bytes.credit", nil)
+	//total amount of bytes debited
+	mBytesDebit = metrics.NewRegisteredCounterForced("account.bytes.debit", nil)
+	//total amount of credited messages
+	mMsgCredit = metrics.NewRegisteredCounterForced("account.msg.credit", nil)
+	//total amount of debited messages
+	mMsgDebit = metrics.NewRegisteredCounterForced("account.msg.debit", nil)
+	//how many times local node had to drop remote peers
+	mPeerDrops = metrics.NewRegisteredCounterForced("account.peerdrops", nil)
+	//how many times local node overdrafted and dropped
+	mSelfDrops = metrics.NewRegisteredCounterForced("account.selfdrops", nil)
+)
+
+//Prices defines how prices are being passed on to the accounting instance
+type Prices interface {
+	//Return the Price for a message
+	Price(interface{}) *Price
+}
+
+type Payer bool
+
+const (
+	Sender   = Payer(true)
+	Receiver = Payer(false)
+)
+
+//Price represents the costs of a message
+type Price struct {
+	Value   uint64 //
+	PerByte bool   //True if the price is per byte or for unit
+	Payer   Payer
+}
+
+//For gives back the price for a message
+//A protocol provides the message price in absolute value
+//This method then returns the correct signed amount,
+//depending on who pays, which is identified by the `payer` argument:
+//`Send` will pass a `Sender` payer, `Receive` will pass the `Receiver` argument.
+//Thus: If Sending and sender pays, amount positive, otherwise negative
+//If Receiving, and receiver pays, amount positive, otherwise negative
+func (p *Price) For(payer Payer, size uint32) int64 {
+	price := p.Value
+	if p.PerByte {
+		price *= uint64(size)
+	}
+	if p.Payer == payer {
+		return 0 - int64(price)
+	}
+	return int64(price)
+}
+
+//Balance is the actual accounting instance
+//Balance defines the operations needed for accounting
+//Implementations internally maintain the balance for every peer
+type Balance interface {
+	//Adds amount to the local balance with remote node `peer`;
+	//positive amount = credit local node
+	//negative amount = debit local node
+	Add(amount int64, peer *Peer) error
+}
+
+//Accounting implements the Hook interface
+//It interfaces to the balances through the Balance interface,
+//while interfacing with protocols and its prices through the Prices interface
+type Accounting struct {
+	Balance //interface to accounting logic
+	Prices  //interface to prices logic
+}
+
+func NewAccounting(balance Balance, po Prices) *Accounting {
+	ah := &Accounting{
+		Prices:  po,
+		Balance: balance,
+	}
+	return ah
+}
+
+//Implement Hook.Send
+// Send takes a peer, a size and a msg and
+// - calculates the cost for the local node sending a msg of size to peer using the Prices interface
+// - credits/debits local node using balance interface
+func (ah *Accounting) Send(peer *Peer, size uint32, msg interface{}) error {
+	//get the price for a message (through the protocol spec)
+	price := ah.Price(msg)
+	//this message doesn't need accounting
+	if price == nil {
+		return nil
+	}
+	//evaluate the price for sending messages
+	costToLocalNode := price.For(Sender, size)
+	//do the accounting
+	err := ah.Add(costToLocalNode, peer)
+	//record metrics: just increase counters for user-facing metrics
+	ah.doMetrics(costToLocalNode, size, err)
+	return err
+}
+
+//Implement Hook.Receive
+// Receive takes a peer, a size and a msg and
+// - calculates the cost for the local node receiving a msg of size from peer using the Prices interface
+// - credits/debits local node using balance interface
+func (ah *Accounting) Receive(peer *Peer, size uint32, msg interface{}) error {
+	//get the price for a message (through the protocol spec)
+	price := ah.Price(msg)
+	//this message doesn't need accounting
+	if price == nil {
+		return nil
+	}
+	//evaluate the price for receiving messages
+	costToLocalNode := price.For(Receiver, size)
+	//do the accounting
+	err := ah.Add(costToLocalNode, peer)
+	//record metrics: just increase counters for user-facing metrics
+	ah.doMetrics(costToLocalNode, size, err)
+	return err
+}
+
+//record some metrics
+//this is not an error handling. `err` is returned by both `Send` and `Receive`
+//`err` will only be non-nil if a limit has been violated (overdraft), in which case the peer has been dropped.
+//if the limit has been violated and `err` is thus not nil:
+// * if the price is positive, local node has been credited; thus `err` implicitly signals the REMOTE has been dropped
+// * if the price is negative, local node has been debited, thus `err` implicitly signals LOCAL node "overdraft"
+func (ah *Accounting) doMetrics(price int64, size uint32, err error) {
+	if price > 0 {
+		mBalanceCredit.Inc(price)
+		mBytesCredit.Inc(int64(size))
+		mMsgCredit.Inc(1)
+		if err != nil {
+			//increase the number of times a remote node has been dropped due to "overdraft"
+			mPeerDrops.Inc(1)
+		}
+	} else {
+		mBalanceDebit.Inc(price)
+		mBytesDebit.Inc(int64(size))
+		mMsgDebit.Inc(1)
+		if err != nil {
+			//increase the number of times the local node has done an "overdraft" in respect to other nodes
+			mSelfDrops.Inc(1)
+		}
+	}
+}