test(exch:bs:strategy) test accounting consistency

> Why expose num bytes sent and received?

    Makes it easy to test consistency of the ledgers

> Got a better reason?

    Makes it possible to expose metrics to the people-facing API

exchange/bitswap/strategy/interface.go

@@ -24,6 +24,10 @@ type Strategy interface {
 
 	// MessageSent records sending of message for accounting purposes
 	MessageSent(*peer.Peer, bsmsg.BitSwapMessage) error
+
+	NumBytesSentTo(*peer.Peer) uint64
+
+	NumBytesReceivedFrom(*peer.Peer) uint64
 }
 
 type WantList interface {

exchange/bitswap/strategy/strategy.go

@@ -76,6 +76,14 @@ func (s *strategist) MessageSent(p *peer.Peer, m bsmsg.BitSwapMessage) error {
 	return nil
 }
 
+func (s *strategist) NumBytesSentTo(p *peer.Peer) uint64 {
+	return s.ledger(p).Accounting.BytesSent
+}
+
+func (s *strategist) NumBytesReceivedFrom(p *peer.Peer) uint64 {
+	return s.ledger(p).Accounting.BytesRecv
+}
+
 // ledger lazily instantiates a ledger
 func (s *strategist) ledger(p *peer.Peer) *ledger {
 	l, ok := s.ledgerMap[peerKey(p.Key())]

exchange/bitswap/strategy/strategy_test.go

@@ -1,11 +1,12 @@
 package strategy
 
 import (
+	"strings"
 	"testing"
 
 	message "github.com/jbenet/go-ipfs/exchange/bitswap/message"
-	"github.com/jbenet/go-ipfs/peer"
-	"github.com/jbenet/go-ipfs/util/testutil"
+	peer "github.com/jbenet/go-ipfs/peer"
+	testutil "github.com/jbenet/go-ipfs/util/testutil"
 )
 
 type peerAndStrategist struct {
@@ -20,6 +21,38 @@ func newPeerAndStrategist(idStr string) peerAndStrategist {
 	}
 }
 
+func TestConsistentAccounting(t *testing.T) {
+	sender := newPeerAndStrategist("Ernie")
+	receiver := newPeerAndStrategist("Bert")
+
+	// Send messages from Ernie to Bert
+	for i := 0; i < 1000; i++ {
+
+		m := message.New()
+		content := []string{"this", "is", "message", "i"}
+		m.AppendBlock(testutil.NewBlockOrFail(t, strings.Join(content, " ")))
+
+		sender.MessageSent(receiver.Peer, m)
+		receiver.MessageReceived(sender.Peer, m)
+	}
+
+	// Ensure sender records the change
+	if sender.NumBytesSentTo(receiver.Peer) == 0 {
+		t.Fatal("Sent bytes were not recorded")
+	}
+
+	// Ensure sender and receiver have the same values
+	if sender.NumBytesSentTo(receiver.Peer) != receiver.NumBytesReceivedFrom(sender.Peer) {
+		t.Fatal("Inconsistent book-keeping. Strategies don't agree")
+	}
+
+	// Ensure sender didn't record receving anything. And that the receiver
+	// didn't record sending anything
+	if receiver.NumBytesSentTo(sender.Peer) != 0 || sender.NumBytesReceivedFrom(receiver.Peer) != 0 {
+		t.Fatal("Bert didn't send bytes to Ernie")
+	}
+}
+
 func TestBlockRecordedAsWantedAfterMessageReceived(t *testing.T) {
 	beggar := newPeerAndStrategist("can't be chooser")
 	chooser := newPeerAndStrategist("chooses JIF")