fix(netxlite): make default resolver converge faster (#456)

* fix(netxlite): make default resolver converge faster

Closes https://github.com/ooni/probe/issues/1726

* Update internal/netxlite/resolver.go

* fix(ndt7): adapt tests after previous change

Because now we're running the DNS resolution inside a goroutine
with a child context, the returned error string is different.

The previous error said we canceled the whole dialing operation,
while now we see directly that the context was canceled.

internal/engine/experiment/ndt7/dial_test.go

@@ -18,8 +18,8 @@ func TestDialDownloadWithCancelledContext(t *testing.T) {
 	cancel() // immediately halt
 	mgr := newDialManager("wss://hostname.fake", log.Log, "miniooni/0.1.0-dev")
 	conn, err := mgr.dialDownload(ctx)
-	if err == nil || !strings.HasSuffix(err.Error(), "operation was canceled") {
-		t.Fatal("not the error we expected")
+	if err == nil || !strings.HasSuffix(err.Error(), "context canceled") {
+		t.Fatal("not the error we expected", err)
 	}
 	if conn != nil {
 		t.Fatal("expected nil conn here")
@@ -31,8 +31,8 @@ func TestDialUploadWithCancelledContext(t *testing.T) {
 	cancel() // immediately halt
 	mgr := newDialManager("wss://hostname.fake", log.Log, "miniooni/0.1.0-dev")
 	conn, err := mgr.dialUpload(ctx)
-	if err == nil || !strings.HasSuffix(err.Error(), "operation was canceled") {
-		t.Fatal("not the error we expected")
+	if err == nil || !strings.HasSuffix(err.Error(), "context canceled") {
+		t.Fatal("not the error we expected", err)
 	}
 	if conn != nil {
 		t.Fatal("expected nil conn here")

internal/engine/experiment/ndt7/ndt7_test.go

@@ -52,8 +52,8 @@ func TestDoDownloadWithCancelledContext(t *testing.T) {
 	err := m.doDownload(
 		ctx, sess, model.NewPrinterCallbacks(log.Log), new(TestKeys),
 		"ws://host.name")
-	if err == nil || !strings.HasSuffix(err.Error(), "operation was canceled") {
-		t.Fatal("not the error we expected")
+	if err == nil || !strings.HasSuffix(err.Error(), "context canceled") {
+		t.Fatal("not the error we expected", err)
 	}
 }
 
@@ -69,8 +69,8 @@ func TestDoUploadWithCancelledContext(t *testing.T) {
 	err := m.doUpload(
 		ctx, sess, model.NewPrinterCallbacks(log.Log), new(TestKeys),
 		"ws://host.name")
-	if err == nil || !strings.HasSuffix(err.Error(), "operation was canceled") {
-		t.Fatal("not the error we expected")
+	if err == nil || !strings.HasSuffix(err.Error(), "context canceled") {
+		t.Fatal("not the error we expected", err)
 	}
 }
 
@@ -132,8 +132,8 @@ func TestFailDownload(t *testing.T) {
 		new(model.Measurement),
 		model.NewPrinterCallbacks(log.Log),
 	)
-	if err == nil || !strings.HasSuffix(err.Error(), "operation was canceled") {
-		t.Fatal(err)
+	if err == nil || !strings.HasSuffix(err.Error(), "context canceled") {
+		t.Fatal("not the error we expected", err)
 	}
 }
 
@@ -153,8 +153,8 @@ func TestFailUpload(t *testing.T) {
 		new(model.Measurement),
 		model.NewPrinterCallbacks(log.Log),
 	)
-	if err == nil || !strings.HasSuffix(err.Error(), "operation was canceled") {
-		t.Fatal(err)
+	if err == nil || !strings.HasSuffix(err.Error(), "context canceled") {
+		t.Fatal("not the error we expected", err)
 	}
 }