refactor: move bytecounter to internal (#391)

It's generic enough to live outside of engine/netx.

Occurred to me while working on https://github.com/ooni/probe/issues/1687.

internal/bytecounter/bytecounter.go

@@ -0,0 +1,61 @@
+// Package bytecounter contains code to track the number of
+// bytes sent and received by a probe.
+package bytecounter
+
+import "github.com/ooni/probe-cli/v3/internal/atomicx"
+
+// Counter counts bytes sent and received.
+type Counter struct {
+	// Received contains the bytes received. You MUST initialize
+	// this field, or you can just use the New factory.
+	Received *atomicx.Int64
+
+	// Sent contains the bytes sent. You MUST initialize
+	// this field, or you can just use the New factory.
+	Sent *atomicx.Int64
+}
+
+// New creates a new Counter.
+func New() *Counter {
+	return &Counter{Received: &atomicx.Int64{}, Sent: &atomicx.Int64{}}
+}
+
+// CountBytesSent adds count to the bytes sent counter.
+func (c *Counter) CountBytesSent(count int) {
+	c.Sent.Add(int64(count))
+}
+
+// CountKibiBytesSent adds 1024*count to the bytes sent counter.
+func (c *Counter) CountKibiBytesSent(count float64) {
+	c.Sent.Add(int64(1024 * count))
+}
+
+// BytesSent returns the bytes sent so far.
+func (c *Counter) BytesSent() int64 {
+	return c.Sent.Load()
+}
+
+// KibiBytesSent returns the KiB sent so far.
+func (c *Counter) KibiBytesSent() float64 {
+	return float64(c.BytesSent()) / 1024
+}
+
+// CountBytesReceived adds count to the bytes received counter.
+func (c *Counter) CountBytesReceived(count int) {
+	c.Received.Add(int64(count))
+}
+
+// CountKibiBytesReceived adds 1024*count to the bytes received counter.
+func (c *Counter) CountKibiBytesReceived(count float64) {
+	c.Received.Add(int64(1024 * count))
+}
+
+// BytesReceived returns the bytes received so far.
+func (c *Counter) BytesReceived() int64 {
+	return c.Received.Load()
+}
+
+// KibiBytesReceived returns the KiB received so far.
+func (c *Counter) KibiBytesReceived() float64 {
+	return float64(c.BytesReceived()) / 1024
+}

internal/bytecounter/bytecounter_test.go

@@ -0,0 +1,23 @@
+package bytecounter
+
+import "testing"
+
+func TestGood(t *testing.T) {
+	counter := New()
+	counter.CountBytesReceived(16384)
+	counter.CountKibiBytesReceived(10)
+	counter.CountBytesSent(2048)
+	counter.CountKibiBytesSent(10)
+	if counter.BytesSent() != 12288 {
+		t.Fatal("invalid bytes sent")
+	}
+	if counter.BytesReceived() != 26624 {
+		t.Fatal("invalid bytes received")
+	}
+	if v := counter.KibiBytesSent(); v < 11.9 || v > 12.1 {
+		t.Fatal("invalid kibibytes sent")
+	}
+	if v := counter.KibiBytesReceived(); v < 25.9 || v > 26.1 {
+		t.Fatal("invalid kibibytes received")
+	}
+}