chore: merge probe-engine into probe-cli (#201)

This is how I did it:

1. `git clone https://github.com/ooni/probe-engine internal/engine`

2. ```
(cd internal/engine && git describe --tags)
v0.23.0
```

3. `nvim go.mod` (merging `go.mod` with `internal/engine/go.mod`

4. `rm -rf internal/.git internal/engine/go.{mod,sum}`

5. `git add internal/engine`

6. `find . -type f -name \*.go -exec sed -i 's@/ooni/probe-engine@/ooni/probe-cli/v3/internal/engine@g' {} \;`

7. `go build ./...` (passes)

8. `go test -race ./...` (temporary failure on RiseupVPN)

9. `go mod tidy`

10. this commit message

Once this piece of work is done, we can build a new version of `ooniprobe` that
is using `internal/engine` directly. We need to do more work to ensure all the
other functionality in `probe-engine` (e.g. making mobile packages) are still WAI.

Part of https://github.com/ooni/probe/issues/1335

internal/engine/netx/resolver/dnsovertcp_test.go

@@ -0,0 +1,146 @@
+package resolver_test
+
+import (
+	"context"
+	"errors"
+	"net"
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/resolver"
+)
+
+func TestDNSOverTCPTransportQueryTooLarge(t *testing.T) {
+	const address = "9.9.9.9:53"
+	txp := resolver.NewDNSOverTCP(new(net.Dialer).DialContext, address)
+	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<18))
+	if err == nil {
+		t.Fatal("expected an error here")
+	}
+	if reply != nil {
+		t.Fatal("expected nil reply here")
+	}
+}
+
+func TestDNSOverTCPTransportDialFailure(t *testing.T) {
+	const address = "9.9.9.9:53"
+	mocked := errors.New("mocked error")
+	fakedialer := resolver.FakeDialer{Err: mocked}
+	txp := resolver.NewDNSOverTCP(fakedialer.DialContext, address)
+	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
+	if !errors.Is(err, mocked) {
+		t.Fatal("not the error we expected")
+	}
+	if reply != nil {
+		t.Fatal("expected nil reply here")
+	}
+}
+
+func TestDNSOverTCPTransportSetDealineFailure(t *testing.T) {
+	const address = "9.9.9.9:53"
+	mocked := errors.New("mocked error")
+	fakedialer := resolver.FakeDialer{Conn: &resolver.FakeConn{
+		SetDeadlineError: mocked,
+	}}
+	txp := resolver.NewDNSOverTCP(fakedialer.DialContext, address)
+	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
+	if !errors.Is(err, mocked) {
+		t.Fatal("not the error we expected")
+	}
+	if reply != nil {
+		t.Fatal("expected nil reply here")
+	}
+}
+
+func TestDNSOverTCPTransportWriteFailure(t *testing.T) {
+	const address = "9.9.9.9:53"
+	mocked := errors.New("mocked error")
+	fakedialer := resolver.FakeDialer{Conn: &resolver.FakeConn{
+		WriteError: mocked,
+	}}
+	txp := resolver.NewDNSOverTCP(fakedialer.DialContext, address)
+	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
+	if !errors.Is(err, mocked) {
+		t.Fatal("not the error we expected")
+	}
+	if reply != nil {
+		t.Fatal("expected nil reply here")
+	}
+}
+
+func TestDNSOverTCPTransportReadFailure(t *testing.T) {
+	const address = "9.9.9.9:53"
+	mocked := errors.New("mocked error")
+	fakedialer := resolver.FakeDialer{Conn: &resolver.FakeConn{
+		ReadError: mocked,
+	}}
+	txp := resolver.NewDNSOverTCP(fakedialer.DialContext, address)
+	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
+	if !errors.Is(err, mocked) {
+		t.Fatal("not the error we expected")
+	}
+	if reply != nil {
+		t.Fatal("expected nil reply here")
+	}
+}
+
+func TestDNSOverTCPTransportSecondReadFailure(t *testing.T) {
+	const address = "9.9.9.9:53"
+	mocked := errors.New("mocked error")
+	fakedialer := resolver.FakeDialer{Conn: &resolver.FakeConn{
+		ReadError: mocked,
+		ReadData:  []byte{byte(0), byte(2)},
+	}}
+	txp := resolver.NewDNSOverTCP(fakedialer.DialContext, address)
+	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
+	if !errors.Is(err, mocked) {
+		t.Fatal("not the error we expected")
+	}
+	if reply != nil {
+		t.Fatal("expected nil reply here")
+	}
+}
+
+func TestDNSOverTCPTransportAllGood(t *testing.T) {
+	const address = "9.9.9.9:53"
+	mocked := errors.New("mocked error")
+	fakedialer := resolver.FakeDialer{Conn: &resolver.FakeConn{
+		ReadError: mocked,
+		ReadData:  []byte{byte(0), byte(1), byte(1)},
+	}}
+	txp := resolver.NewDNSOverTCP(fakedialer.DialContext, address)
+	reply, err := txp.RoundTrip(context.Background(), make([]byte, 1<<11))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(reply) != 1 || reply[0] != 1 {
+		t.Fatal("not the response we expected")
+	}
+}
+
+func TestDNSOverTCPTransportOK(t *testing.T) {
+	const address = "9.9.9.9:53"
+	txp := resolver.NewDNSOverTCP(new(net.Dialer).DialContext, address)
+	if txp.RequiresPadding() != false {
+		t.Fatal("invalid RequiresPadding")
+	}
+	if txp.Network() != "tcp" {
+		t.Fatal("invalid Network")
+	}
+	if txp.Address() != address {
+		t.Fatal("invalid Address")
+	}
+}
+
+func TestDNSOverTLSTransportOK(t *testing.T) {
+	const address = "9.9.9.9:853"
+	txp := resolver.NewDNSOverTLS(resolver.DialTLSContext, address)
+	if txp.RequiresPadding() != true {
+		t.Fatal("invalid RequiresPadding")
+	}
+	if txp.Network() != "dot" {
+		t.Fatal("invalid Network")
+	}
+	if txp.Address() != address {
+		t.Fatal("invalid Address")
+	}
+}