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/probeservices/statefile_test.go

@@ -0,0 +1,153 @@
+package probeservices_test
+
+import (
+	"encoding/json"
+	"errors"
+	"testing"
+	"time"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/ooni/probe-cli/v3/internal/engine/internal/kvstore"
+	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
+)
+
+func TestStateAuth(t *testing.T) {
+	t.Run("with no Token", func(t *testing.T) {
+		state := probeservices.State{Expire: time.Now().Add(10 * time.Hour)}
+		if state.Auth() != nil {
+			t.Fatal("expected nil here")
+		}
+	})
+	t.Run("with expired Token", func(t *testing.T) {
+		state := probeservices.State{
+			Expire: time.Now().Add(-1 * time.Hour),
+			Token:  "xx-x-xxx-xx",
+		}
+		if state.Auth() != nil {
+			t.Fatal("expected nil here")
+		}
+	})
+	t.Run("with good Token", func(t *testing.T) {
+		state := probeservices.State{
+			Expire: time.Now().Add(10 * time.Hour),
+			Token:  "xx-x-xxx-xx",
+		}
+		if state.Auth() == nil {
+			t.Fatal("expected valid auth here")
+		}
+	})
+}
+
+func TestStateCredentials(t *testing.T) {
+	t.Run("with no ClientID", func(t *testing.T) {
+		state := probeservices.State{}
+		if state.Credentials() != nil {
+			t.Fatal("expected nil here")
+		}
+	})
+	t.Run("with no Password", func(t *testing.T) {
+		state := probeservices.State{
+			ClientID: "xx-x-xxx-xx",
+		}
+		if state.Credentials() != nil {
+			t.Fatal("expected nil here")
+		}
+	})
+	t.Run("with all good", func(t *testing.T) {
+		state := probeservices.State{
+			ClientID: "xx-x-xxx-xx",
+			Password: "xx",
+		}
+		if state.Credentials() == nil {
+			t.Fatal("expected valid auth here")
+		}
+	})
+}
+
+func TestStateFileMemoryIntegration(t *testing.T) {
+	// Does the StateFile have the property that we can write
+	// values into it and then read again the same files?
+	sf := probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore())
+	s := probeservices.State{
+		Expire:   time.Now(),
+		Password: "xy",
+		Token:    "abc",
+		ClientID: "xx",
+	}
+	if err := sf.Set(s); err != nil {
+		t.Fatal(err)
+	}
+	os := sf.Get()
+	diff := cmp.Diff(s, os)
+	if diff != "" {
+		t.Fatal(diff)
+	}
+}
+
+func TestStateFileSetMarshalError(t *testing.T) {
+	sf := probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore())
+	s := probeservices.State{
+		Expire:   time.Now(),
+		Password: "xy",
+		Token:    "abc",
+		ClientID: "xx",
+	}
+	expected := errors.New("mocked error")
+	failingfunc := func(v interface{}) ([]byte, error) {
+		return nil, expected
+	}
+	if err := sf.SetMockable(s, failingfunc); !errors.Is(err, expected) {
+		t.Fatal("not the error we expected")
+	}
+}
+
+func TestStateFileGetKVStoreGetError(t *testing.T) {
+	sf := probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore())
+	expected := errors.New("mocked error")
+	failingfunc := func(string) ([]byte, error) {
+		return nil, expected
+	}
+	s, err := sf.GetMockable(failingfunc, json.Unmarshal)
+	if !errors.Is(err, expected) {
+		t.Fatal("not the error we expected")
+	}
+	if s.ClientID != "" {
+		t.Fatal("unexpected ClientID field")
+	}
+	if !s.Expire.IsZero() {
+		t.Fatal("unexpected Expire field")
+	}
+	if s.Password != "" {
+		t.Fatal("unexpected Password field")
+	}
+	if s.Token != "" {
+		t.Fatal("unexpected Token field")
+	}
+}
+
+func TestStateFileGetUnmarshalError(t *testing.T) {
+	sf := probeservices.NewStateFile(kvstore.NewMemoryKeyValueStore())
+	if err := sf.Set(probeservices.State{}); err != nil {
+		t.Fatal(err)
+	}
+	expected := errors.New("mocked error")
+	failingfunc := func([]byte, interface{}) error {
+		return expected
+	}
+	s, err := sf.GetMockable(sf.Store.Get, failingfunc)
+	if !errors.Is(err, expected) {
+		t.Fatal("not the error we expected")
+	}
+	if s.ClientID != "" {
+		t.Fatal("unexpected ClientID field")
+	}
+	if !s.Expire.IsZero() {
+		t.Fatal("unexpected Expire field")
+	}
+	if s.Password != "" {
+		t.Fatal("unexpected Password field")
+	}
+	if s.Token != "" {
+		t.Fatal("unexpected Token field")
+	}
+}