MVP of fleetctl preview command (#51)

This adds a `fleetctl preview` command to fleetctl that will download
and start https://github.com/fleetdm/osquery-in-a-box. This is
potentially the easiest way for a user to try out Fleet.

cmd/fleetctl/fleetctl.go

@@ -45,6 +45,7 @@ func main() {
 		goqueryCommand(),
 		userCommand(),
 		debugCommand(),
+		previewCommand(),
 	}
 
 	app.RunAndExitOnError()

cmd/fleetctl/preview.go

@@ -0,0 +1,174 @@
+package main
+
+import (
+	"archive/zip"
+	"bytes"
+	"crypto/tls"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+
+	"github.com/cenkalti/backoff/v4"
+	"github.com/pkg/errors"
+	"github.com/urfave/cli"
+)
+
+const (
+	previewDirectory = "fleet-preview"
+	downloadUrl      = "https://github.com/fleetdm/osquery-in-a-box/archive/master.zip"
+)
+
+func previewCommand() cli.Command {
+	return cli.Command{
+		Name:  "preview",
+		Usage: "Set up a preview deployment of the Fleet server",
+		UsageText: `Set up a preview deployment of the Fleet server using Docker and docker-compose. Docker tools must be available in the environment.
+
+This command will create a directory fleet-preview in the current working directory. Configurations can be modified in that directory.`,
+		Subcommands: []cli.Command{},
+		Action: func(c *cli.Context) error {
+			if _, err := exec.LookPath("docker-compose"); err != nil {
+				return errors.New("Please install Docker (https://docs.docker.com/get-docker/).")
+			}
+
+			// Download files if necessary
+			if _, err := os.Stat(
+				filepath.Join(previewDirectory, "docker-compose.yml"),
+			); err != nil {
+				fmt.Println("Downloading dependencies into", previewDirectory)
+				if err := downloadFiles(); err != nil {
+					return errors.Wrap(err, "Error downloading dependencies")
+				}
+			}
+
+			if err := os.Chdir(previewDirectory); err != nil {
+				return err
+			}
+
+			fmt.Println("Starting Docker containers...")
+			out, err := exec.Command("docker-compose", "up", "-d", "mysql01", "redis01", "fleet01").CombinedOutput()
+			if err != nil {
+				fmt.Println(string(out))
+				return errors.Errorf("Failed to run docker-compose")
+			}
+
+			if err := waitStartup(); err != nil {
+				return errors.Wrap(err, "wait for server startup")
+			}
+
+			fmt.Println("Fleet is now available at https://localhost:8412.")
+			fmt.Println("Note: You can safely ignore the browser warning \"Your connection is not private\". Click through this warning using the \"Advanced\" option.")
+
+			return nil
+		},
+	}
+}
+
+func downloadFiles() error {
+	resp, err := http.Get(downloadUrl)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode != http.StatusOK {
+		return errors.Errorf("download got status %d", resp.StatusCode)
+	}
+
+	zipContents, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return errors.Wrap(err, "read download contents")
+	}
+
+	zipReader, err := zip.NewReader(bytes.NewReader(zipContents), int64(len(zipContents)))
+	if err != nil {
+		return errors.Wrap(err, "open download contents for unzip")
+	}
+	// zip.NewReader does not need to be closed (and cannot be)
+
+	if err := unzip(zipReader); err != nil {
+		return errors.Wrap(err, "unzip download contents")
+	}
+
+	return nil
+}
+
+// Adapted from https://stackoverflow.com/a/24792688/491710
+func unzip(r *zip.Reader) error {
+	// Closure to address file descriptors issue with all the deferred .Close()
+	// methods
+	extractAndWriteFile := func(f *zip.File) error {
+		rc, err := f.Open()
+		if err != nil {
+			return err
+		}
+		defer rc.Close()
+
+		path := f.Name
+		path = strings.Replace(path, "osquery-in-a-box-master", "fleet-preview", 1)
+
+		// We don't need to check for directory traversal as we are already
+		// trusting the validity of this ZIP file.
+
+		if f.FileInfo().IsDir() {
+			if err := os.MkdirAll(path, f.Mode()); err != nil {
+				return err
+			}
+		} else {
+			if err := os.MkdirAll(filepath.Dir(path), f.Mode()); err != nil {
+				return err
+			}
+			f, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, f.Mode())
+			if err != nil {
+				return err
+			}
+			defer f.Close()
+
+			_, err = io.Copy(f, rc)
+			if err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+
+	for _, f := range r.File {
+		err := extractAndWriteFile(f)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func waitStartup() error {
+	fmt.Println("Waiting for server to start up...")
+	client := &http.Client{
+		Transport: &http.Transport{
+			TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
+		},
+	}
+	if err := backoff.Retry(
+		func() error {
+			resp, err := client.Get("https://localhost:8412/healthz")
+			if err != nil {
+				return err
+			}
+			if resp.StatusCode != http.StatusOK {
+				return errors.Errorf("got status code %d", resp.StatusCode)
+			}
+			return nil
+		},
+		backoff.NewExponentialBackOff(),
+	); err != nil {
+		return errors.Wrap(err, "checking server health")
+	}
+
+	return nil
+}