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/integration_test.go

@@ -0,0 +1,93 @@
+package netx_test
+
+import (
+	"context"
+	"errors"
+	"io/ioutil"
+	"net/http"
+	"testing"
+
+	"github.com/apex/log"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/bytecounter"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/errorx"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/trace"
+)
+
+func TestSuccess(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skip test in short mode")
+	}
+	log.SetLevel(log.DebugLevel)
+	counter := bytecounter.New()
+	config := netx.Config{
+		BogonIsError:        true,
+		ByteCounter:         counter,
+		CacheResolutions:    true,
+		ContextByteCounting: true,
+		DialSaver:           &trace.Saver{},
+		HTTPSaver:           &trace.Saver{},
+		Logger:              log.Log,
+		ReadWriteSaver:      &trace.Saver{},
+		ResolveSaver:        &trace.Saver{},
+		TLSSaver:            &trace.Saver{},
+	}
+	txp := netx.NewHTTPTransport(config)
+	client := &http.Client{Transport: txp}
+	resp, err := client.Get("https://www.google.com")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err = ioutil.ReadAll(resp.Body); err != nil {
+		t.Fatal(err)
+	}
+	if err = resp.Body.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if counter.Sent.Load() <= 0 {
+		t.Fatal("no bytes sent?!")
+	}
+	if counter.Received.Load() <= 0 {
+		t.Fatal("no bytes received?!")
+	}
+	if ev := config.DialSaver.Read(); len(ev) <= 0 {
+		t.Fatal("no dial events?!")
+	}
+	if ev := config.HTTPSaver.Read(); len(ev) <= 0 {
+		t.Fatal("no HTTP events?!")
+	}
+	if ev := config.ReadWriteSaver.Read(); len(ev) <= 0 {
+		t.Fatal("no R/W events?!")
+	}
+	if ev := config.ResolveSaver.Read(); len(ev) <= 0 {
+		t.Fatal("no resolver events?!")
+	}
+	if ev := config.TLSSaver.Read(); len(ev) <= 0 {
+		t.Fatal("no TLS events?!")
+	}
+}
+
+func TestBogonResolutionNotBroken(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skip test in short mode")
+	}
+	saver := new(trace.Saver)
+	r := netx.NewResolver(netx.Config{
+		BogonIsError: true,
+		DNSCache: map[string][]string{
+			"www.google.com": {"127.0.0.1"},
+		},
+		ResolveSaver: saver,
+		Logger:       log.Log,
+	})
+	addrs, err := r.LookupHost(context.Background(), "www.google.com")
+	if !errors.Is(err, errorx.ErrDNSBogon) {
+		t.Fatal("not the error we expected")
+	}
+	if err.Error() != errorx.FailureDNSBogonError {
+		t.Fatal("error not correctly wrapped")
+	}
+	if len(addrs) != 1 || addrs[0] != "127.0.0.1" {
+		t.Fatal("address was not returned")
+	}
+}