refactor(ndt7): use netxlite rather than netx (#768)

This diff required us to move some code around, but no major
change actually happened, except better tests.

While there, I also slightly refactored ndt7's implementation and
removed the ProxyURL setting, which was actually unused.

See https://github.com/ooni/probe/issues/2121

internal/engine/netx/dialer/bytecounter.go

@@ -1,26 +1,5 @@
 package dialer
 
-import (
-	"context"
-	"net"
+import "github.com/ooni/probe-cli/v3/internal/bytecounter"
 
-	"github.com/ooni/probe-cli/v3/internal/bytecounter"
-	"github.com/ooni/probe-cli/v3/internal/model"
-)
-
-// byteCounterDialer is a byte-counting-aware dialer. To perform byte counting, you
-// should make sure that you insert this dialer in the dialing chain.
-type byteCounterDialer struct {
-	model.Dialer
-}
-
-// DialContext implements Dialer.DialContext
-func (d *byteCounterDialer) DialContext(
-	ctx context.Context, network, address string) (net.Conn, error) {
-	conn, err := d.Dialer.DialContext(ctx, network, address)
-	if err != nil {
-		return nil, err
-	}
-	conn = bytecounter.MaybeWrapWithContextByteCounters(ctx, conn)
-	return conn, nil
-}
+type byteCounterDialer = bytecounter.ContextAwareDialer

internal/engine/netx/dialer/bytecounter_test.go

@@ -1,91 +0,0 @@
-package dialer
-
-import (
-	"context"
-	"errors"
-	"io"
-	"net"
-	"net/http"
-	"testing"
-
-	"github.com/ooni/probe-cli/v3/internal/bytecounter"
-	"github.com/ooni/probe-cli/v3/internal/model/mocks"
-	"github.com/ooni/probe-cli/v3/internal/netxlite"
-)
-
-func dorequest(ctx context.Context, url string) error {
-	txp := http.DefaultTransport.(*http.Transport).Clone()
-	defer txp.CloseIdleConnections()
-	dialer := &byteCounterDialer{Dialer: netxlite.DefaultDialer}
-	txp.DialContext = dialer.DialContext
-	client := &http.Client{Transport: txp}
-	req, err := http.NewRequestWithContext(ctx, "GET", "http://www.google.com", nil)
-	if err != nil {
-		return err
-	}
-	resp, err := client.Do(req)
-	if err != nil {
-		return err
-	}
-	if _, err := netxlite.CopyContext(ctx, io.Discard, resp.Body); err != nil {
-		return err
-	}
-	return resp.Body.Close()
-}
-
-func TestByteCounterNormalUsage(t *testing.T) {
-	if testing.Short() {
-		t.Skip("skip test in short mode")
-	}
-	sess := bytecounter.New()
-	ctx := context.Background()
-	ctx = bytecounter.WithSessionByteCounter(ctx, sess)
-	if err := dorequest(ctx, "http://www.google.com"); err != nil {
-		t.Fatal(err)
-	}
-	exp := bytecounter.New()
-	ctx = bytecounter.WithExperimentByteCounter(ctx, exp)
-	if err := dorequest(ctx, "http://facebook.com"); err != nil {
-		t.Fatal(err)
-	}
-	if exp.Received.Load() <= 0 {
-		t.Fatal("experiment should have received some bytes")
-	}
-	if sess.Received.Load() <= exp.Received.Load() {
-		t.Fatal("session should have received more than experiment")
-	}
-	if exp.Sent.Load() <= 0 {
-		t.Fatal("experiment should have sent some bytes")
-	}
-	if sess.Sent.Load() <= exp.Sent.Load() {
-		t.Fatal("session should have sent more than experiment")
-	}
-}
-
-func TestByteCounterNoHandlers(t *testing.T) {
-	if testing.Short() {
-		t.Skip("skip test in short mode")
-	}
-	ctx := context.Background()
-	if err := dorequest(ctx, "http://www.google.com"); err != nil {
-		t.Fatal(err)
-	}
-	if err := dorequest(ctx, "http://facebook.com"); err != nil {
-		t.Fatal(err)
-	}
-}
-
-func TestByteCounterConnectFailure(t *testing.T) {
-	dialer := &byteCounterDialer{Dialer: &mocks.Dialer{
-		MockDialContext: func(ctx context.Context, network string, address string) (net.Conn, error) {
-			return nil, io.EOF
-		},
-	}}
-	conn, err := dialer.DialContext(context.Background(), "tcp", "www.google.com:80")
-	if !errors.Is(err, io.EOF) {
-		t.Fatal("not the error we expected")
-	}
-	if conn != nil {
-		t.Fatal("expected nil conn here")
-	}
-}