feat: tlsmiddlebox experiment (#817)

See https://github.com/ooni/probe/issues/2124

internal/engine/experiment/tlsmiddlebox/config_test.go

@@ -0,0 +1,83 @@
+package tlsmiddlebox
+
+import (
+	"testing"
+	"time"
+)
+
+func TestConfig_maxttl(t *testing.T) {
+	c := Config{}
+	if c.maxttl() != 20 {
+		t.Fatal("invalid default number of repetitions")
+	}
+}
+
+func TestConfig_delay(t *testing.T) {
+	c := Config{}
+	if c.delay() != 100*time.Millisecond {
+		t.Fatal("invalid default delay")
+	}
+}
+
+func TestConfig_resolver(t *testing.T) {
+	c := Config{}
+	if c.resolverURL() != "https://mozilla.cloudflare-dns.com/dns-query" {
+		t.Fatal("invalid resolver URL")
+	}
+}
+
+func TestConfig_snipass(t *testing.T) {
+	c := Config{}
+	if c.snicontrol() != "example.com" {
+		t.Fatal("invalid pass SNI")
+	}
+}
+
+func TestConfig_testhelper(t *testing.T) {
+	t.Run("without config", func(t *testing.T) {
+		c := Config{}
+		th, err := c.testhelper("example.com")
+		if err != nil {
+			t.Fatal("unexpected error")
+		}
+		if th.Scheme != "tlshandshake" {
+			t.Fatal("unexpected scheme")
+		}
+		if th.Host != "example.com" {
+			t.Fatal("unexpected host")
+		}
+	})
+
+	t.Run("with config", func(t *testing.T) {
+		c := Config{
+			TestHelper: "tlshandshake://example.com:80",
+		}
+		th, err := c.testhelper("google.com")
+		if err != nil {
+			t.Fatal("unexpected error")
+		}
+		if th.Scheme != "tlshandshake" {
+			t.Fatal("unexpected scheme")
+		}
+		if th.Host != "example.com:80" {
+			t.Fatal("unexpected host")
+		}
+	})
+
+	t.Run("failure case", func(t *testing.T) {
+		c := Config{
+			TestHelper: "\t",
+		}
+		th, _ := c.testhelper("google.com")
+		if th != nil {
+			t.Fatal("expected nil url")
+		}
+	})
+}
+
+func TestConfig_clientid(t *testing.T) {
+	c := Config{}
+	if c.clientid() != 0 {
+		t.Fatal("invalid default ClientHello ID")
+	}
+}