Log a throughput summary for each connection

This will increase transparency for people running standalone proxies
and help us debug any potential issues with proxies behaving unreliably.

proxy/util.go

@@ -0,0 +1,84 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+type BytesLogger interface {
+	AddOutbound(int)
+	AddInbound(int)
+	ThroughputSummary() string
+}
+
+// Default BytesLogger does nothing.
+type BytesNullLogger struct{}
+
+func (b BytesNullLogger) AddOutbound(amount int)    {}
+func (b BytesNullLogger) AddInbound(amount int)     {}
+func (b BytesNullLogger) ThroughputSummary() string { return "" }
+
+// BytesSyncLogger uses channels to safely log from multiple sources with output
+// occuring at reasonable intervals.
+type BytesSyncLogger struct {
+	outboundChan, inboundChan              chan int
+	outbound, inbound, outEvents, inEvents int
+	start                                  time.Time
+}
+
+// NewBytesSyncLogger returns a new BytesSyncLogger and starts it loggin.
+func NewBytesSyncLogger() *BytesSyncLogger {
+	b := &BytesSyncLogger{
+		outboundChan: make(chan int, 5),
+		inboundChan:  make(chan int, 5),
+	}
+	go b.log()
+	b.start = time.Now()
+	return b
+}
+
+func (b *BytesSyncLogger) log() {
+	for {
+		select {
+		case amount := <-b.outboundChan:
+			b.outbound += amount
+			b.outEvents++
+		case amount := <-b.inboundChan:
+			b.inbound += amount
+			b.inEvents++
+		}
+	}
+}
+
+func (b *BytesSyncLogger) AddOutbound(amount int) {
+	b.outboundChan <- amount
+}
+
+func (b *BytesSyncLogger) AddInbound(amount int) {
+	b.inboundChan <- amount
+}
+
+func (b *BytesSyncLogger) ThroughputSummary() string {
+	var inUnit, outUnit string
+	units := []string{"B", "KB", "MB", "GB"}
+
+	inbound := b.inbound
+	outbound := b.outbound
+
+	for i, u := range units {
+		inUnit = u
+		if (inbound < 1000) || (i == len(units)-1) {
+			break
+		}
+		inbound = inbound / 1000
+	}
+	for i, u := range units {
+		outUnit = u
+		if (outbound < 1000) || (i == len(units)-1) {
+			break
+		}
+		outbound = outbound / 1000
+	}
+	t := time.Now()
+	return fmt.Sprintf("Traffic throughput (up|down): %d %s|%d %s -- (%d OnMessages, %d Sends, over %d seconds)", inbound, inUnit, outbound, outUnit, b.outEvents, b.inEvents, int(t.Sub(b.start).Seconds()))
+}