refactor(netx): move dns transports in netxlite/dnsx (#503)

While there, modernize the way in which we run tests to avoid
depending on the fake files scattered around the tree and to
use some well defined mock structures instead.

Part of https://github.com/ooni/probe/issues/1591

internal/engine/netx/resolver/legacy.go

@@ -0,0 +1,28 @@
+package resolver
+
+import "github.com/ooni/probe-cli/v3/internal/netxlite/dnsx"
+
+// Variables that other packages expect to find here but have been
+// moved into the internal/netxlite/dnsx package.
+var (
+	NewSerialResolver               = dnsx.NewSerialResolver
+	NewDNSOverUDP                   = dnsx.NewDNSOverUDP
+	NewDNSOverTCP                   = dnsx.NewDNSOverTCP
+	NewDNSOverTLS                   = dnsx.NewDNSOverTLS
+	NewDNSOverHTTPS                 = dnsx.NewDNSOverHTTPS
+	NewDNSOverHTTPSWithHostOverride = dnsx.NewDNSOverHTTPSWithHostOverride
+)
+
+// Types that other packages expect to find here but have been
+// moved into the internal/netxlite/dnsx package.
+type (
+	DNSOverHTTPS    = dnsx.DNSOverHTTPS
+	DNSOverTCP      = dnsx.DNSOverTCP
+	DNSOverUDP      = dnsx.DNSOverUDP
+	MiekgEncoder    = dnsx.MiekgEncoder
+	MiekgDecoder    = dnsx.MiekgDecoder
+	RoundTripper    = dnsx.RoundTripper
+	SerialResolver  = dnsx.SerialResolver
+	Dialer          = dnsx.Dialer
+	DialContextFunc = dnsx.DialContextFunc
+)

internal/netxlite/dnsx/decoder.go

@@ -1,4 +1,4 @@
-package resolver
+package dnsx
 
 import (
 	"errors"

internal/netxlite/dnsx/decoder_test.go

@@ -1,6 +1,7 @@
-package resolver
+package dnsx
 
 import (
+	"net"
 	"strings"
 	"testing"
 
@@ -20,7 +21,7 @@ func TestDecoderUnpackError(t *testing.T) {
 
 func TestDecoderNXDOMAIN(t *testing.T) {
 	d := &MiekgDecoder{}
-	data, err := d.Decode(dns.TypeA, GenReplyError(t, dns.RcodeNameError))
+	data, err := d.Decode(dns.TypeA, genReplyError(t, dns.RcodeNameError))
 	if err == nil || !strings.HasSuffix(err.Error(), "no such host") {
 		t.Fatal("not the error we expected")
 	}
@@ -31,7 +32,7 @@ func TestDecoderNXDOMAIN(t *testing.T) {
 
 func TestDecoderOtherError(t *testing.T) {
 	d := &MiekgDecoder{}
-	data, err := d.Decode(dns.TypeA, GenReplyError(t, dns.RcodeRefused))
+	data, err := d.Decode(dns.TypeA, genReplyError(t, dns.RcodeRefused))
 	if err == nil || !strings.HasSuffix(err.Error(), "query failed") {
 		t.Fatal("not the error we expected")
 	}
@@ -42,7 +43,7 @@ func TestDecoderOtherError(t *testing.T) {
 
 func TestDecoderNoAddress(t *testing.T) {
 	d := &MiekgDecoder{}
-	data, err := d.Decode(dns.TypeA, GenReplySuccess(t, dns.TypeA))
+	data, err := d.Decode(dns.TypeA, genReplySuccess(t, dns.TypeA))
 	if err == nil || !strings.HasSuffix(err.Error(), "no response returned") {
 		t.Fatal("not the error we expected")
 	}
@@ -54,7 +55,7 @@ func TestDecoderNoAddress(t *testing.T) {
 func TestDecoderDecodeA(t *testing.T) {
 	d := &MiekgDecoder{}
 	data, err := d.Decode(
-		dns.TypeA, GenReplySuccess(t, dns.TypeA, "1.1.1.1", "8.8.8.8"))
+		dns.TypeA, genReplySuccess(t, dns.TypeA, "1.1.1.1", "8.8.8.8"))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -72,7 +73,7 @@ func TestDecoderDecodeA(t *testing.T) {
 func TestDecoderDecodeAAAA(t *testing.T) {
 	d := &MiekgDecoder{}
 	data, err := d.Decode(
-		dns.TypeAAAA, GenReplySuccess(t, dns.TypeAAAA, "::1", "fe80::1"))
+		dns.TypeAAAA, genReplySuccess(t, dns.TypeAAAA, "::1", "fe80::1"))
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -90,7 +91,7 @@ func TestDecoderDecodeAAAA(t *testing.T) {
 func TestDecoderUnexpectedAReply(t *testing.T) {
 	d := &MiekgDecoder{}
 	data, err := d.Decode(
-		dns.TypeA, GenReplySuccess(t, dns.TypeAAAA, "::1", "fe80::1"))
+		dns.TypeA, genReplySuccess(t, dns.TypeAAAA, "::1", "fe80::1"))
 	if err == nil || !strings.HasSuffix(err.Error(), "no response returned") {
 		t.Fatal("not the error we expected")
 	}
@@ -102,7 +103,7 @@ func TestDecoderUnexpectedAReply(t *testing.T) {
 func TestDecoderUnexpectedAAAAReply(t *testing.T) {
 	d := &MiekgDecoder{}
 	data, err := d.Decode(
-		dns.TypeAAAA, GenReplySuccess(t, dns.TypeA, "1.1.1.1", "8.8.4.4."))
+		dns.TypeAAAA, genReplySuccess(t, dns.TypeA, "1.1.1.1", "8.8.4.4."))
 	if err == nil || !strings.HasSuffix(err.Error(), "no response returned") {
 		t.Fatal("not the error we expected")
 	}
@@ -110,3 +111,71 @@ func TestDecoderUnexpectedAAAAReply(t *testing.T) {
 		t.Fatal("expected nil data here")
 	}
 }
+
+func genReplyError(t *testing.T, code int) []byte {
+	question := dns.Question{
+		Name:   dns.Fqdn("x.org"),
+		Qtype:  dns.TypeA,
+		Qclass: dns.ClassINET,
+	}
+	query := new(dns.Msg)
+	query.Id = dns.Id()
+	query.RecursionDesired = true
+	query.Question = make([]dns.Question, 1)
+	query.Question[0] = question
+	reply := new(dns.Msg)
+	reply.Compress = true
+	reply.MsgHdr.RecursionAvailable = true
+	reply.SetRcode(query, code)
+	data, err := reply.Pack()
+	if err != nil {
+		t.Fatal(err)
+	}
+	return data
+}
+
+func genReplySuccess(t *testing.T, qtype uint16, ips ...string) []byte {
+	question := dns.Question{
+		Name:   dns.Fqdn("x.org"),
+		Qtype:  qtype,
+		Qclass: dns.ClassINET,
+	}
+	query := new(dns.Msg)
+	query.Id = dns.Id()
+	query.RecursionDesired = true
+	query.Question = make([]dns.Question, 1)
+	query.Question[0] = question
+	reply := new(dns.Msg)
+	reply.Compress = true
+	reply.MsgHdr.RecursionAvailable = true
+	reply.SetReply(query)
+	for _, ip := range ips {
+		switch qtype {
+		case dns.TypeA:
+			reply.Answer = append(reply.Answer, &dns.A{
+				Hdr: dns.RR_Header{
+					Name:   dns.Fqdn("x.org"),
+					Rrtype: qtype,
+					Class:  dns.ClassINET,
+					Ttl:    0,
+				},
+				A: net.ParseIP(ip),
+			})
+		case dns.TypeAAAA:
+			reply.Answer = append(reply.Answer, &dns.AAAA{
+				Hdr: dns.RR_Header{
+					Name:   dns.Fqdn("x.org"),
+					Rrtype: qtype,
+					Class:  dns.ClassINET,
+					Ttl:    0,
+				},
+				AAAA: net.ParseIP(ip),
+			})
+		}
+	}
+	data, err := reply.Pack()
+	if err != nil {
+		t.Fatal(err)
+	}
+	return data
+}

internal/netxlite/dnsx/dnsoverhttps.go

@@ -1,4 +1,4 @@
-package resolver
+package dnsx
 
 import (
 	"bytes"

internal/netxlite/dnsx/dnsoverhttps_test.go

@@ -1,4 +1,4 @@
-package resolver
+package dnsx
 
 import (
 	"bytes"

internal/netxlite/dnsx/dnsovertcp.go

@@ -1,4 +1,4 @@
-package resolver
+package dnsx
 
 import (
 	"context"

internal/netxlite/dnsx/dnsovertcp_test.go

@@ -1,10 +1,16 @@
-package resolver
+package dnsx
 
 import (
+	"bytes"
 	"context"
+	"crypto/tls"
 	"errors"
+	"io"
 	"net"
 	"testing"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/netxlite/mocks"
 )
 
 func TestDNSOverTCPTransportQueryTooLarge(t *testing.T) {
@@ -22,7 +28,11 @@ func TestDNSOverTCPTransportQueryTooLarge(t *testing.T) {
 func TestDNSOverTCPTransportDialFailure(t *testing.T) {
 	const address = "9.9.9.9:53"
 	mocked := errors.New("mocked error")
-	fakedialer := FakeDialer{Err: mocked}
+	fakedialer := &mocks.Dialer{
+		MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
+			return nil, mocked
+		},
+	}
 	txp := NewDNSOverTCP(fakedialer.DialContext, address)
 	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
 	if !errors.Is(err, mocked) {
@@ -36,9 +46,18 @@ func TestDNSOverTCPTransportDialFailure(t *testing.T) {
 func TestDNSOverTCPTransportSetDealineFailure(t *testing.T) {
 	const address = "9.9.9.9:53"
 	mocked := errors.New("mocked error")
-	fakedialer := FakeDialer{Conn: &FakeConn{
+	fakedialer := &mocks.Dialer{
-		SetDeadlineError: mocked,
+		MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
-	}}
+			return &mocks.Conn{
+				MockSetDeadline: func(t time.Time) error {
+					return mocked
+				},
+				MockClose: func() error {
+					return nil
+				},
+			}, nil
+		},
+	}
 	txp := NewDNSOverTCP(fakedialer.DialContext, address)
 	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
 	if !errors.Is(err, mocked) {
@@ -52,9 +71,21 @@ func TestDNSOverTCPTransportSetDealineFailure(t *testing.T) {
 func TestDNSOverTCPTransportWriteFailure(t *testing.T) {
 	const address = "9.9.9.9:53"
 	mocked := errors.New("mocked error")
-	fakedialer := FakeDialer{Conn: &FakeConn{
+	fakedialer := &mocks.Dialer{
-		WriteError: mocked,
+		MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
-	}}
+			return &mocks.Conn{
+				MockSetDeadline: func(t time.Time) error {
+					return nil
+				},
+				MockWrite: func(b []byte) (int, error) {
+					return 0, mocked
+				},
+				MockClose: func() error {
+					return nil
+				},
+			}, nil
+		},
+	}
 	txp := NewDNSOverTCP(fakedialer.DialContext, address)
 	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
 	if !errors.Is(err, mocked) {
@@ -68,9 +99,24 @@ func TestDNSOverTCPTransportWriteFailure(t *testing.T) {
 func TestDNSOverTCPTransportReadFailure(t *testing.T) {
 	const address = "9.9.9.9:53"
 	mocked := errors.New("mocked error")
-	fakedialer := FakeDialer{Conn: &FakeConn{
+	fakedialer := &mocks.Dialer{
-		ReadError: mocked,
+		MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
-	}}
+			return &mocks.Conn{
+				MockSetDeadline: func(t time.Time) error {
+					return nil
+				},
+				MockWrite: func(b []byte) (int, error) {
+					return len(b), nil
+				},
+				MockRead: func(b []byte) (int, error) {
+					return 0, mocked
+				},
+				MockClose: func() error {
+					return nil
+				},
+			}, nil
+		},
+	}
 	txp := NewDNSOverTCP(fakedialer.DialContext, address)
 	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
 	if !errors.Is(err, mocked) {
@@ -84,10 +130,30 @@ func TestDNSOverTCPTransportReadFailure(t *testing.T) {
 func TestDNSOverTCPTransportSecondReadFailure(t *testing.T) {
 	const address = "9.9.9.9:53"
 	mocked := errors.New("mocked error")
-	fakedialer := FakeDialer{Conn: &FakeConn{
+	input := io.MultiReader(
-		ReadError: mocked,
+		bytes.NewReader([]byte{byte(0), byte(2)}),
-		ReadData:  []byte{byte(0), byte(2)},
+		&mocks.Reader{
-	}}
+			MockRead: func(b []byte) (int, error) {
+				return 0, mocked
+			},
+		},
+	)
+	fakedialer := &mocks.Dialer{
+		MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
+			return &mocks.Conn{
+				MockSetDeadline: func(t time.Time) error {
+					return nil
+				},
+				MockWrite: func(b []byte) (int, error) {
+					return len(b), nil
+				},
+				MockRead: input.Read,
+				MockClose: func() error {
+					return nil
+				},
+			}, nil
+		},
+	}
 	txp := NewDNSOverTCP(fakedialer.DialContext, address)
 	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
 	if !errors.Is(err, mocked) {
@@ -100,11 +166,23 @@ func TestDNSOverTCPTransportSecondReadFailure(t *testing.T) {
 
 func TestDNSOverTCPTransportAllGood(t *testing.T) {
 	const address = "9.9.9.9:53"
-	mocked := errors.New("mocked error")
+	input := bytes.NewReader([]byte{byte(0), byte(1), byte(1)})
-	fakedialer := FakeDialer{Conn: &FakeConn{
+	fakedialer := &mocks.Dialer{
-		ReadError: mocked,
+		MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
-		ReadData:  []byte{byte(0), byte(1), byte(1)},
+			return &mocks.Conn{
-	}}
+				MockSetDeadline: func(t time.Time) error {
+					return nil
+				},
+				MockWrite: func(b []byte) (int, error) {
+					return len(b), nil
+				},
+				MockRead: input.Read,
+				MockClose: func() error {
+					return nil
+				},
+			}, nil
+		},
+	}
 	txp := NewDNSOverTCP(fakedialer.DialContext, address)
 	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
 	if err != nil {
@@ -131,7 +209,7 @@ func TestDNSOverTCPTransportOK(t *testing.T) {
 
 func TestDNSOverTLSTransportOK(t *testing.T) {
 	const address = "9.9.9.9:853"
-	txp := NewDNSOverTLS(DialTLSContext, address)
+	txp := NewDNSOverTLS((&tls.Dialer{}).DialContext, address)
 	if txp.RequiresPadding() != true {
 		t.Fatal("invalid RequiresPadding")
 	}

internal/netxlite/dnsx/dnsoverudp.go

@@ -1,4 +1,4 @@
-package resolver
+package dnsx
 
 import (
 	"context"

internal/netxlite/dnsx/dnsoverudp_test.go

@@ -1,16 +1,24 @@
-package resolver
+package dnsx
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"net"
 	"testing"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/netxlite/mocks"
 )
 
 func TestDNSOverUDPDialFailure(t *testing.T) {
 	mocked := errors.New("mocked error")
 	const address = "9.9.9.9:53"
-	txp := NewDNSOverUDP(FakeDialer{Err: mocked}, address)
+	txp := NewDNSOverUDP(&mocks.Dialer{
+		MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
+			return nil, mocked
+		},
+	}, address)
 	data, err := txp.RoundTrip(context.Background(), nil)
 	if !errors.Is(err, mocked) {
 		t.Fatal("not the error we expected")
@@ -23,9 +31,16 @@ func TestDNSOverUDPDialFailure(t *testing.T) {
 func TestDNSOverUDPSetDeadlineError(t *testing.T) {
 	mocked := errors.New("mocked error")
 	txp := NewDNSOverUDP(
-		FakeDialer{
+		&mocks.Dialer{
-			Conn: &FakeConn{
+			MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
-				SetDeadlineError: mocked,
+				return &mocks.Conn{
+					MockSetDeadline: func(t time.Time) error {
+						return mocked
+					},
+					MockClose: func() error {
+						return nil
+					},
+				}, nil
 			},
 		}, "9.9.9.9:53",
 	)
@@ -41,9 +56,19 @@ func TestDNSOverUDPSetDeadlineError(t *testing.T) {
 func TestDNSOverUDPWriteFailure(t *testing.T) {
 	mocked := errors.New("mocked error")
 	txp := NewDNSOverUDP(
-		FakeDialer{
+		&mocks.Dialer{
-			Conn: &FakeConn{
+			MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
-				WriteError: mocked,
+				return &mocks.Conn{
+					MockSetDeadline: func(t time.Time) error {
+						return nil
+					},
+					MockWrite: func(b []byte) (int, error) {
+						return 0, mocked
+					},
+					MockClose: func() error {
+						return nil
+					},
+				}, nil
 			},
 		}, "9.9.9.9:53",
 	)
@@ -59,9 +84,22 @@ func TestDNSOverUDPWriteFailure(t *testing.T) {
 func TestDNSOverUDPReadFailure(t *testing.T) {
 	mocked := errors.New("mocked error")
 	txp := NewDNSOverUDP(
-		FakeDialer{
+		&mocks.Dialer{
-			Conn: &FakeConn{
+			MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
-				ReadError: mocked,
+				return &mocks.Conn{
+					MockSetDeadline: func(t time.Time) error {
+						return nil
+					},
+					MockWrite: func(b []byte) (int, error) {
+						return len(b), nil
+					},
+					MockRead: func(b []byte) (int, error) {
+						return 0, mocked
+					},
+					MockClose: func() error {
+						return nil
+					},
+				}, nil
 			},
 		}, "9.9.9.9:53",
 	)
@@ -76,9 +114,23 @@ func TestDNSOverUDPReadFailure(t *testing.T) {
 
 func TestDNSOverUDPReadSuccess(t *testing.T) {
 	const expected = 17
+	input := bytes.NewReader(make([]byte, expected))
 	txp := NewDNSOverUDP(
-		FakeDialer{
+		&mocks.Dialer{
-			Conn: &FakeConn{ReadData: make([]byte, 17)},
+			MockDialContext: func(ctx context.Context, network, address string) (net.Conn, error) {
+				return &mocks.Conn{
+					MockSetDeadline: func(t time.Time) error {
+						return nil
+					},
+					MockWrite: func(b []byte) (int, error) {
+						return len(b), nil
+					},
+					MockRead: input.Read,
+					MockClose: func() error {
+						return nil
+					},
+				}, nil
+			},
 		}, "9.9.9.9:53",
 	)
 	data, err := txp.RoundTrip(context.Background(), nil)

internal/netxlite/dnsx/encoder.go

@@ -1,4 +1,4 @@
-package resolver
+package dnsx
 
 import "github.com/miekg/dns"
 

internal/netxlite/dnsx/encoder_test.go

@@ -1,4 +1,4 @@
-package resolver
+package dnsx
 
 import (
 	"strings"

internal/netxlite/dnsx/mocks/decoder.go

@@ -0,0 +1,11 @@
+package mocks
+
+// Decoder allows mocking dnsx.Decoder.
+type Decoder struct {
+	MockDecode func(qtype uint16, reply []byte) ([]string, error)
+}
+
+// Decode calls MockDecode.
+func (e *Decoder) Decode(qtype uint16, reply []byte) ([]string, error) {
+	return e.MockDecode(qtype, reply)
+}

internal/netxlite/dnsx/mocks/decoder_test.go

@@ -0,0 +1,26 @@
+package mocks
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestDecoder(t *testing.T) {
+	t.Run("Decode", func(t *testing.T) {
+		expected := errors.New("mocked error")
+		e := &Decoder{
+			MockDecode: func(qtype uint16, reply []byte) ([]string, error) {
+				return nil, expected
+			},
+		}
+		out, err := e.Decode(dns.TypeA, make([]byte, 17))
+		if !errors.Is(err, expected) {
+			t.Fatal("unexpected err", err)
+		}
+		if out != nil {
+			t.Fatal("unexpected out")
+		}
+	})
+}

internal/netxlite/dnsx/mocks/doc.go

@@ -0,0 +1,2 @@
+// Package mocks contains mocks for dnsx.
+package mocks

internal/netxlite/dnsx/mocks/encoder.go

@@ -0,0 +1,11 @@
+package mocks
+
+// Encoder allows mocking dnsx.Encoder.
+type Encoder struct {
+	MockEncode func(domain string, qtype uint16, padding bool) ([]byte, error)
+}
+
+// Encode calls MockEncode.
+func (e *Encoder) Encode(domain string, qtype uint16, padding bool) ([]byte, error) {
+	return e.MockEncode(domain, qtype, padding)
+}

internal/netxlite/dnsx/mocks/encoder_test.go

@@ -0,0 +1,26 @@
+package mocks
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestEncoder(t *testing.T) {
+	t.Run("Encode", func(t *testing.T) {
+		expected := errors.New("mocked error")
+		e := &Encoder{
+			MockEncode: func(domain string, qtype uint16, padding bool) ([]byte, error) {
+				return nil, expected
+			},
+		}
+		out, err := e.Encode("dns.google", dns.TypeA, true)
+		if !errors.Is(err, expected) {
+			t.Fatal("unexpected err", err)
+		}
+		if out != nil {
+			t.Fatal("unexpected out")
+		}
+	})
+}

internal/netxlite/dnsx/mocks/roundtripper.go

@@ -0,0 +1,41 @@
+package mocks
+
+import "context"
+
+// RoundTripper allows mocking dnsx.RoundTripper.
+type RoundTripper struct {
+	MockRoundTrip func(ctx context.Context, query []byte) (reply []byte, err error)
+
+	MockRequiresPadding func() bool
+
+	MockNetwork func() string
+
+	MockAddress func() string
+
+	MockCloseIdleConnections func()
+}
+
+// RoundTrip calls MockRoundTrip.
+func (txp *RoundTripper) RoundTrip(ctx context.Context, query []byte) (reply []byte, err error) {
+	return txp.MockRoundTrip(ctx, query)
+}
+
+// RequiresPadding calls MockRequiresPadding.
+func (txp *RoundTripper) RequiresPadding() bool {
+	return txp.MockRequiresPadding()
+}
+
+// Network calls MockNetwork.
+func (txp *RoundTripper) Network() string {
+	return txp.MockNetwork()
+}
+
+// Address calls MockAddress.
+func (txp *RoundTripper) Address() string {
+	return txp.MockAddress()
+}
+
+// CloseIdleConnections calls MockCloseIdleConnections.
+func (txp *RoundTripper) CloseIdleConnections() {
+	txp.MockCloseIdleConnections()
+}

internal/netxlite/dnsx/mocks/roundtripper_test.go

@@ -0,0 +1,73 @@
+package mocks
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/atomicx"
+)
+
+func TestRoundTripper(t *testing.T) {
+	t.Run("RoundTrip", func(t *testing.T) {
+		expected := errors.New("mocked error")
+		txp := &RoundTripper{
+			MockRoundTrip: func(ctx context.Context, query []byte) ([]byte, error) {
+				return nil, expected
+			},
+		}
+		resp, err := txp.RoundTrip(context.Background(), make([]byte, 16))
+		if !errors.Is(err, expected) {
+			t.Fatal("not the error we expected", err)
+		}
+		if resp != nil {
+			t.Fatal("expected nil response here")
+		}
+	})
+
+	t.Run("RequiresPadding", func(t *testing.T) {
+		txp := &RoundTripper{
+			MockRequiresPadding: func() bool {
+				return true
+			},
+		}
+		if txp.RequiresPadding() != true {
+			t.Fatal("unexpected result")
+		}
+	})
+
+	t.Run("Network", func(t *testing.T) {
+		txp := &RoundTripper{
+			MockNetwork: func() string {
+				return "antani"
+			},
+		}
+		if txp.Network() != "antani" {
+			t.Fatal("unexpected result")
+		}
+	})
+
+	t.Run("Address", func(t *testing.T) {
+		txp := &RoundTripper{
+			MockAddress: func() string {
+				return "mascetti"
+			},
+		}
+		if txp.Address() != "mascetti" {
+			t.Fatal("unexpected result")
+		}
+	})
+
+	t.Run("CloseIdleConnections", func(t *testing.T) {
+		called := &atomicx.Int64{}
+		txp := &RoundTripper{
+			MockCloseIdleConnections: func() {
+				called.Add(1)
+			},
+		}
+		txp.CloseIdleConnections()
+		if called.Load() != 1 {
+			t.Fatal("not called")
+		}
+	})
+}

internal/netxlite/dnsx/roundtripper.go

@@ -0,0 +1,21 @@
+package dnsx
+
+import "context"
+
+// RoundTripper represents an abstract DNS transport.
+type RoundTripper interface {
+	// RoundTrip sends a DNS query and receives the reply.
+	RoundTrip(ctx context.Context, query []byte) (reply []byte, err error)
+
+	// RequiresPadding return true for DoH and DoT according to RFC8467
+	RequiresPadding() bool
+
+	// Network is the network of the round tripper (e.g. "dot")
+	Network() string
+
+	// Address is the address of the round tripper (e.g. "1.1.1.1:853")
+	Address() string
+
+	// CloseIdleConnections closes idle connections.
+	CloseIdleConnections()
+}

internal/netxlite/dnsx/serial.go

@@ -1,4 +1,4 @@
-package resolver
+package dnsx
 
 import (
 	"context"
@@ -9,24 +9,6 @@ import (
 	"github.com/ooni/probe-cli/v3/internal/atomicx"
 )
 
-// RoundTripper represents an abstract DNS transport.
-type RoundTripper interface {
-	// RoundTrip sends a DNS query and receives the reply.
-	RoundTrip(ctx context.Context, query []byte) (reply []byte, err error)
-
-	// RequiresPadding return true for DoH and DoT according to RFC8467
-	RequiresPadding() bool
-
-	// Network is the network of the round tripper (e.g. "dot")
-	Network() string
-
-	// Address is the address of the round tripper (e.g. "1.1.1.1:853")
-	Address() string
-
-	// CloseIdleConnections closes idle connections.
-	CloseIdleConnections()
-}
-
 // SerialResolver is a resolver that first issues an A query and then
 // issues an AAAA query for the requested domain.
 type SerialResolver struct {
@@ -117,5 +99,3 @@ func (r *SerialResolver) roundTrip(
 	}
 	return r.Decoder.Decode(qtype, replydata)
 }
-
-var _ Resolver = &SerialResolver{}

internal/netxlite/dnsx/serial_test.go

@@ -1,20 +1,21 @@
-package resolver_test
+package dnsx
 
 import (
 	"context"
+	"crypto/tls"
 	"errors"
 	"net"
 	"strings"
-	"syscall"
 	"testing"
 
 	"github.com/miekg/dns"
-	"github.com/ooni/probe-cli/v3/internal/engine/netx/resolver"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/dnsx/mocks"
+	"github.com/ooni/probe-cli/v3/internal/netxlite/errorsx"
 )
 
 func TestOONIGettingTransport(t *testing.T) {
-	txp := resolver.NewDNSOverTLS(resolver.DialTLSContext, "8.8.8.8:853")
+	txp := NewDNSOverTLS((&tls.Dialer{}).DialContext, "8.8.8.8:853")
-	r := resolver.NewSerialResolver(txp)
+	r := NewSerialResolver(txp)
 	rtx := r.Transport()
 	if rtx.Network() != "dot" || rtx.Address() != "8.8.8.8:853" {
 		t.Fatal("not the transport we expected")
@@ -29,8 +30,15 @@ func TestOONIGettingTransport(t *testing.T) {
 
 func TestOONIEncodeError(t *testing.T) {
 	mocked := errors.New("mocked error")
-	txp := resolver.NewDNSOverTLS(resolver.DialTLSContext, "8.8.8.8:853")
+	txp := NewDNSOverTLS((&tls.Dialer{}).DialContext, "8.8.8.8:853")
-	r := resolver.SerialResolver{Encoder: resolver.FakeEncoder{Err: mocked}, Txp: txp}
+	r := SerialResolver{
+		Encoder: &mocks.Encoder{
+			MockEncode: func(domain string, qtype uint16, padding bool) ([]byte, error) {
+				return nil, mocked
+			},
+		},
+		Txp: txp,
+	}
 	addrs, err := r.LookupHost(context.Background(), "www.gogle.com")
 	if !errors.Is(err, mocked) {
 		t.Fatal("not the error we expected")
@@ -42,8 +50,15 @@ func TestOONIEncodeError(t *testing.T) {
 
 func TestOONIRoundTripError(t *testing.T) {
 	mocked := errors.New("mocked error")
-	txp := resolver.FakeTransport{Err: mocked}
+	txp := &mocks.RoundTripper{
-	r := resolver.NewSerialResolver(txp)
+		MockRoundTrip: func(ctx context.Context, query []byte) (reply []byte, err error) {
+			return nil, mocked
+		},
+		MockRequiresPadding: func() bool {
+			return true
+		},
+	}
+	r := NewSerialResolver(txp)
 	addrs, err := r.LookupHost(context.Background(), "www.gogle.com")
 	if !errors.Is(err, mocked) {
 		t.Fatal("not the error we expected")
@@ -54,8 +69,15 @@ func TestOONIRoundTripError(t *testing.T) {
 }
 
 func TestOONIWithEmptyReply(t *testing.T) {
-	txp := resolver.FakeTransport{Data: resolver.GenReplySuccess(t, dns.TypeA)}
+	txp := &mocks.RoundTripper{
-	r := resolver.NewSerialResolver(txp)
+		MockRoundTrip: func(ctx context.Context, query []byte) (reply []byte, err error) {
+			return genReplySuccess(t, dns.TypeA), nil
+		},
+		MockRequiresPadding: func() bool {
+			return true
+		},
+	}
+	r := NewSerialResolver(txp)
 	addrs, err := r.LookupHost(context.Background(), "www.gogle.com")
 	if err == nil || !strings.HasSuffix(err.Error(), "no response returned") {
 		t.Fatal("not the error we expected")
@@ -66,10 +88,15 @@ func TestOONIWithEmptyReply(t *testing.T) {
 }
 
 func TestOONIWithAReply(t *testing.T) {
-	txp := resolver.FakeTransport{
+	txp := &mocks.RoundTripper{
-		Data: resolver.GenReplySuccess(t, dns.TypeA, "8.8.8.8"),
+		MockRoundTrip: func(ctx context.Context, query []byte) (reply []byte, err error) {
+			return genReplySuccess(t, dns.TypeA, "8.8.8.8"), nil
+		},
+		MockRequiresPadding: func() bool {
+			return true
+		},
 	}
-	r := resolver.NewSerialResolver(txp)
+	r := NewSerialResolver(txp)
 	addrs, err := r.LookupHost(context.Background(), "www.gogle.com")
 	if err != nil {
 		t.Fatal(err)
@@ -80,10 +107,15 @@ func TestOONIWithAReply(t *testing.T) {
 }
 
 func TestOONIWithAAAAReply(t *testing.T) {
-	txp := resolver.FakeTransport{
+	txp := &mocks.RoundTripper{
-		Data: resolver.GenReplySuccess(t, dns.TypeAAAA, "::1"),
+		MockRoundTrip: func(ctx context.Context, query []byte) (reply []byte, err error) {
+			return genReplySuccess(t, dns.TypeAAAA, "::1"), nil
+		},
+		MockRequiresPadding: func() bool {
+			return true
+		},
 	}
-	r := resolver.NewSerialResolver(txp)
+	r := NewSerialResolver(txp)
 	addrs, err := r.LookupHost(context.Background(), "www.gogle.com")
 	if err != nil {
 		t.Fatal(err)
@@ -94,12 +126,17 @@ func TestOONIWithAAAAReply(t *testing.T) {
 }
 
 func TestOONIWithTimeout(t *testing.T) {
-	txp := resolver.FakeTransport{
+	txp := &mocks.RoundTripper{
-		Err: &net.OpError{Err: syscall.ETIMEDOUT, Op: "dial"},
+		MockRoundTrip: func(ctx context.Context, query []byte) (reply []byte, err error) {
+			return nil, &net.OpError{Err: errorsx.ETIMEDOUT, Op: "dial"}
+		},
+		MockRequiresPadding: func() bool {
+			return true
+		},
 	}
-	r := resolver.NewSerialResolver(txp)
+	r := NewSerialResolver(txp)
 	addrs, err := r.LookupHost(context.Background(), "www.gogle.com")
-	if !errors.Is(err, syscall.ETIMEDOUT) {
+	if !errors.Is(err, errorsx.ETIMEDOUT) {
 		t.Fatal("not the error we expected")
 	}
 	if addrs != nil {