Add Tailscale unstable channel and repo HEAD to integration tests

In preparation for the implementation of the new TS2021 protocol (Tailscale control protocol v2) we are expanding the test infrastructure

integration_common_test.go

@@ -20,7 +20,7 @@ var (
 	IpPrefix4 = netaddr.MustParseIPPrefix("100.64.0.0/10")
 	IpPrefix6 = netaddr.MustParseIPPrefix("fd7a:115c:a1e0::/48")
 
-	tailscaleVersions = []string{"1.22.0", "1.20.4", "1.18.2", "1.16.2", "1.14.3", "1.12.3"}
+	tailscaleVersions = []string{"HEAD", "unstable", "1.22.0", "1.20.4", "1.18.2", "1.16.2", "1.14.3", "1.12.3"}
 )
 
 type TestNamespace struct {
@@ -128,6 +128,49 @@ func DockerAllowNetworkAdministration(config *docker.HostConfig) {
 	})
 }
 
+func getDockerBuildOptions(version string) *dockertest.BuildOptions {
+	var tailscaleBuildOptions *dockertest.BuildOptions
+	switch version {
+	case "HEAD":
+		tailscaleBuildOptions = &dockertest.BuildOptions{
+			Dockerfile: "Dockerfile.tailscale-HEAD",
+			ContextDir: ".",
+			BuildArgs:  []docker.BuildArg{},
+		}
+	case "unstable":
+		tailscaleBuildOptions = &dockertest.BuildOptions{
+			Dockerfile: "Dockerfile.tailscale",
+			ContextDir: ".",
+			BuildArgs: []docker.BuildArg{
+				{
+					Name:  "TAILSCALE_VERSION",
+					Value: "*", // Installs the latest version https://askubuntu.com/a/824926
+				},
+				{
+					Name:  "TAILSCALE_CHANNEL",
+					Value: "unstable",
+				},
+			},
+		}
+	default:
+		tailscaleBuildOptions = &dockertest.BuildOptions{
+			Dockerfile: "Dockerfile.tailscale",
+			ContextDir: ".",
+			BuildArgs: []docker.BuildArg{
+				{
+					Name:  "TAILSCALE_VERSION",
+					Value: version,
+				},
+				{
+					Name:  "TAILSCALE_CHANNEL",
+					Value: "stable",
+				},
+			},
+		}
+	}
+	return tailscaleBuildOptions
+}
+
 func getIPs(
 	tailscales map[string]dockertest.Resource,
 ) (map[string][]netaddr.IP, error) {