Make TLS setup work automatically

This commit injects the per-test-generated tls certs into the tailscale
container and makes sure all can ping all. It does not test any of the
DERP isolation yet.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

integration/integrationutil/util.go

@@ -0,0 +1,77 @@
+package integrationutil
+
+import (
+	"archive/tar"
+	"bytes"
+	"fmt"
+	"io"
+	"log"
+	"path/filepath"
+
+	"github.com/juanfont/headscale/integration/dockertestutil"
+	"github.com/ory/dockertest/v3"
+	"github.com/ory/dockertest/v3/docker"
+)
+
+func WriteFileToContainer(
+	pool *dockertest.Pool,
+	container *dockertest.Resource,
+	path string,
+	data []byte,
+) error {
+	dirPath, fileName := filepath.Split(path)
+
+	file := bytes.NewReader(data)
+
+	buf := bytes.NewBuffer([]byte{})
+
+	tarWriter := tar.NewWriter(buf)
+
+	header := &tar.Header{
+		Name: fileName,
+		Size: file.Size(),
+		// Mode:    int64(stat.Mode()),
+		// ModTime: stat.ModTime(),
+	}
+
+	err := tarWriter.WriteHeader(header)
+	if err != nil {
+		return fmt.Errorf("failed write file header to tar: %w", err)
+	}
+
+	_, err = io.Copy(tarWriter, file)
+	if err != nil {
+		return fmt.Errorf("failed to copy file to tar: %w", err)
+	}
+
+	err = tarWriter.Close()
+	if err != nil {
+		return fmt.Errorf("failed to close tar: %w", err)
+	}
+
+	log.Printf("tar: %s", buf.String())
+
+	// Ensure the directory is present inside the container
+	_, _, err = dockertestutil.ExecuteCommand(
+		container,
+		[]string{"mkdir", "-p", dirPath},
+		[]string{},
+	)
+	if err != nil {
+		return fmt.Errorf("failed to ensure directory: %w", err)
+	}
+
+	err = pool.Client.UploadToContainer(
+		container.Container.ID,
+		docker.UploadToContainerOptions{
+			NoOverwriteDirNonDir: false,
+			Path:                 dirPath,
+			InputStream:          bytes.NewReader(buf.Bytes()),
+		},
+	)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}