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/experiment/tlstool/tlstool.go

@@ -0,0 +1,177 @@
+// Package tlstool contains a TLS tool that we are currently using
+// for running quick and dirty experiments. This tool will change
+// without notice and may be removed without notice.
+//
+// Caveats
+//
+// In particular, this experiment MAY panic when passed incorrect
+// input. This is acceptable because this is not production ready code.
+package tlstool
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/experiment/tlstool/internal"
+	"github.com/ooni/probe-cli/v3/internal/engine/internal/runtimex"
+	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx"
+	"github.com/ooni/probe-cli/v3/internal/engine/netx/archival"
+)
+
+const (
+	testName    = "tlstool"
+	testVersion = "0.1.0"
+)
+
+// Config contains the experiment configuration.
+type Config struct {
+	Delay int64  `ooni:"Milliseconds to wait between writes"`
+	SNI   string `ooni:"Force using the specified SNI"`
+}
+
+// TestKeys contains the experiment results.
+type TestKeys struct {
+	Experiment map[string]*ExperimentKeys `json:"experiment"`
+}
+
+// ExperimentKeys contains the specific experiment results.
+type ExperimentKeys struct {
+	Failure *string `json:"failure"`
+}
+
+// Measurer performs the measurement.
+type Measurer struct {
+	config Config
+}
+
+// ExperimentName implements ExperimentMeasurer.ExperiExperimentName.
+func (m Measurer) ExperimentName() string {
+	return testName
+}
+
+// ExperimentVersion implements ExperimentMeasurer.ExperimentVersion.
+func (m Measurer) ExperimentVersion() string {
+	return testVersion
+}
+
+type method struct {
+	name      string
+	newDialer func(internal.DialerConfig) internal.Dialer
+}
+
+var allMethods = []method{{
+	name:      "vanilla",
+	newDialer: internal.NewVanillaDialer,
+}, {
+	name:      "snisplit",
+	newDialer: internal.NewSNISplitterDialer,
+}, {
+	name:      "random",
+	newDialer: internal.NewRandomSplitterDialer,
+}, {
+	name:      "thrice",
+	newDialer: internal.NewThriceSplitterDialer,
+}}
+
+// Run implements ExperimentMeasurer.Run.
+func (m Measurer) Run(
+	ctx context.Context,
+	sess model.ExperimentSession,
+	measurement *model.Measurement,
+	callbacks model.ExperimentCallbacks,
+) error {
+	// TODO(bassosimone): wondering whether this experiment should
+	// actually be merged with sniblocking instead?
+	tk := new(TestKeys)
+	tk.Experiment = make(map[string]*ExperimentKeys)
+	measurement.TestKeys = tk
+	address := string(measurement.Input)
+	for idx, meth := range allMethods {
+		// TODO(bassosimone): here we actually want to use urlgetter
+		// if possible and collect standard test keys.
+		err := m.run(ctx, runConfig{
+			address:   address,
+			logger:    sess.Logger(),
+			newDialer: meth.newDialer,
+		})
+		percent := float64(idx) / float64(len(allMethods))
+		callbacks.OnProgress(percent, fmt.Sprintf("%s: %+v", meth.name, err))
+		tk.Experiment[meth.name] = &ExperimentKeys{
+			Failure: archival.NewFailure(err),
+		}
+	}
+	return nil
+}
+
+func (m Measurer) newDialer(logger model.Logger) netx.Dialer {
+	// TODO(bassosimone): this is a resolver that should hopefully work
+	// in many places. Maybe allow to configure it?
+	resolver, err := netx.NewDNSClientWithOverrides(netx.Config{Logger: logger},
+		"https://cloudflare.com/dns-query", "dns.cloudflare.com", "", "")
+	runtimex.PanicOnError(err, "cannot initialize resolver")
+	return netx.NewDialer(netx.Config{FullResolver: resolver, Logger: logger})
+}
+
+type runConfig struct {
+	address   string
+	logger    model.Logger
+	newDialer func(internal.DialerConfig) internal.Dialer
+}
+
+func (m Measurer) run(ctx context.Context, config runConfig) error {
+	dialer := config.newDialer(internal.DialerConfig{
+		Dialer: m.newDialer(config.logger),
+		Delay:  time.Duration(m.config.Delay) * time.Millisecond,
+		SNI:    m.pattern(config.address),
+	})
+	tdialer := netx.NewTLSDialer(netx.Config{
+		Dialer:    dialer,
+		Logger:    config.logger,
+		TLSConfig: m.tlsConfig(),
+	})
+	conn, err := tdialer.DialTLSContext(ctx, "tcp", config.address)
+	if err != nil {
+		return err
+	}
+	conn.Close()
+	return nil
+}
+
+func (m Measurer) tlsConfig() *tls.Config {
+	if m.config.SNI != "" {
+		return &tls.Config{ServerName: m.config.SNI}
+	}
+	return nil
+}
+
+func (m Measurer) pattern(address string) string {
+	if m.config.SNI != "" {
+		return m.config.SNI
+	}
+	addr, _, err := net.SplitHostPort(address)
+	// TODO(bassosimone): replace this panic with proper error checking.
+	runtimex.PanicOnError(err, "cannot split address")
+	return addr
+}
+
+// NewExperimentMeasurer creates a new ExperimentMeasurer.
+func NewExperimentMeasurer(config Config) model.ExperimentMeasurer {
+	return Measurer{config: config}
+}
+
+// SummaryKeys contains summary keys for this experiment.
+//
+// Note that this structure is part of the ABI contract with probe-cli
+// therefore we should be careful when changing it.
+type SummaryKeys struct {
+	IsAnomaly bool `json:"-"`
+}
+
+// GetSummaryKeys implements model.ExperimentMeasurer.GetSummaryKeys.
+func (m Measurer) GetSummaryKeys(measurement *model.Measurement) (interface{}, error) {
+	return SummaryKeys{IsAnomaly: false}, nil
+}