1 files changed, 93 insertions, 0 deletions
diff --git a/swarm/swap/swap.go b/swarm/swap/swap.go
new file mode 100644
index 000000000..137eb141d
--- /dev/null
+++ b/swarm/swap/swap.go
@@ -0,0 +1,93 @@
+// 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 swap
+
+import (
+	"errors"
+	"fmt"
+	"strconv"
+	"sync"
+
+	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/p2p/protocols"
+	"github.com/ethereum/go-ethereum/swarm/log"
+	"github.com/ethereum/go-ethereum/swarm/state"
+)
+
+// SwAP Swarm Accounting Protocol
+// a peer to peer micropayment system
+// A node maintains an individual balance with every peer
+// Only messages which have a price will be accounted for
+type Swap struct {
+	stateStore state.Store        //stateStore is needed in order to keep balances across sessions
+	lock       sync.RWMutex       //lock the balances
+	balances   map[enode.ID]int64 //map of balances for each peer
+}
+
+// New - swap constructor
+func New(stateStore state.Store) (swap *Swap) {
+	swap = &Swap{
+		stateStore: stateStore,
+		balances:   make(map[enode.ID]int64),
+	}
+	return
+}
+
+//Swap implements the protocols.Balance interface
+//Add is the (sole) accounting function
+func (s *Swap) Add(amount int64, peer *protocols.Peer) (err error) {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+
+	//load existing balances from the state store
+	err = s.loadState(peer)
+	if err != nil && err != state.ErrNotFound {
+		return
+	}
+	//adjust the balance
+	//if amount is negative, it will decrease, otherwise increase
+	s.balances[peer.ID()] += amount
+	//save the new balance to the state store
+	peerBalance := s.balances[peer.ID()]
+	err = s.stateStore.Put(peer.ID().String(), &peerBalance)
+
+	log.Debug(fmt.Sprintf("balance for peer %s: %s", peer.ID().String(), strconv.FormatInt(peerBalance, 10)))
+	return err
+}
+
+//GetPeerBalance returns the balance for a given peer
+func (swap *Swap) GetPeerBalance(peer enode.ID) (int64, error) {
+	swap.lock.RLock()
+	defer swap.lock.RUnlock()
+	if p, ok := swap.balances[peer]; ok {
+		return p, nil
+	}
+	return 0, errors.New("Peer not found")
+}
+
+//load balances from the state store (persisted)
+func (s *Swap) loadState(peer *protocols.Peer) (err error) {
+	var peerBalance int64
+	peerID := peer.ID()
+	//only load if the current instance doesn't already have this peer's
+	//balance in memory
+	if _, ok := s.balances[peerID]; !ok {
+		err = s.stateStore.Get(peerID.String(), &peerBalance)
+		s.balances[peerID] = peerBalance
+	}
+	return
+}