Add Google Cloud provider

For authentication:
1) Looks for GCLOUD_OAUTH_TOKEN (usually set in ~/.hostctl)
2) Tries detecting OAuth credentials managed by "gcloud auth"
3) Opens browser for web-based OAuth (will save to ~/.hostctl)

Since Google Cloud doesn't allow "." in instance names, provides an interface
to override the default naming convention for the "scale" command.

google/aliases.go

@@ -0,0 +1,27 @@
+package google
+
+type ImageAlias struct {
+	Project string
+	Name    string
+}
+
+var PublicAliases = map[string]ImageAlias{
+	"centos-6":           ImageAlias{"centos-cloud", "centos-6"},
+	"centos-7":           ImageAlias{"centos-cloud", "centos-7"},
+	"container-vm":       ImageAlias{"google-containers", "container-vm"},
+	"coreos":             ImageAlias{"coreos-cloud", "coreos-stable"},
+	"debian-7":           ImageAlias{"debian-cloud", "debian-7-wheezy"},
+	"debian-7-backports": ImageAlias{"debian-cloud", "backports-debian-7-wheezy"},
+	"debian-8":           ImageAlias{"debian-cloud", "debian-8-jessie"},
+	"opensuse-13":        ImageAlias{"opensuse-cloud", "opensuse-13"},
+	"rhel-6":             ImageAlias{"rhel-cloud", "rhel-6"},
+	"rhel-7":             ImageAlias{"rhel-cloud", "rhel-7"},
+	"sles-11":            ImageAlias{"suse-cloud", "sles-11"},
+	"sles-12":            ImageAlias{"suse-cloud", "sles-12"},
+	"ubuntu-12-04":       ImageAlias{"ubuntu-os-cloud", "ubuntu-1204-precise"},
+	"ubuntu-14-04":       ImageAlias{"ubuntu-os-cloud", "ubuntu-1404-trusty"},
+	"ubuntu-14-10":       ImageAlias{"ubuntu-os-cloud", "ubuntu-1410-utopic"},
+	"ubuntu-15-04":       ImageAlias{"ubuntu-os-cloud", "ubuntu-1504-vivid"},
+	"windows-2008-r2":    ImageAlias{"windows-cloud", "windows-server-2008-r2"},
+	"windows-2012-r2":    ImageAlias{"windows-cloud", "windows-server-2012-r2"},
+}

google/provider.go

@@ -0,0 +1,366 @@
+package google
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"google.golang.org/api/compute/v1"
+	"google.golang.org/api/googleapi"
+
+	"github.com/MattAitchison/env"
+	"github.com/gliderlabs/hostctl/providers"
+	"github.com/mitchellh/go-homedir"
+	"golang.org/x/net/context"
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/google"
+)
+
+var envSet = env.NewEnvSet("google")
+
+func init() {
+	readEnv()
+	providers.Register(new(googleCloudProvider), "google")
+}
+
+// default config using client credentials from the "gcloud" tool
+var defaultOAuthConfig = oauth2.Config{
+	ClientID:     "32555940559.apps.googleusercontent.com",
+	ClientSecret: "ZmssLNjJy2998hD4CTg2ejr2",
+	Endpoint:     google.Endpoint,
+	Scopes: []string{
+		compute.DevstorageFullControlScope,
+		compute.ComputeScope,
+	},
+}
+
+func readEnv() {
+	envSet.Clear()
+	envSet.String("GCLOUD_PROJECT", "", "Google project identifier")
+	envSet.String("GCLOUD_OAUTH_TOKEN", "", "OAuth token (saved automatically to ~/.hostctl after authentication)")
+}
+
+type googleCloudProvider struct {
+	service *compute.Service
+	project string
+	region  string
+}
+
+func (p *googleCloudProvider) HostNamePattern() string {
+	return "{{.Namespace}}{{.Name}}-{{.Index}}"
+}
+
+func (p *googleCloudProvider) Setup() error {
+	readEnv()
+
+	p.region = os.Getenv("HOSTCTL_REGION")
+	p.project = envSet.Var("GCLOUD_PROJECT").Value.Get().(string)
+
+	if p.region == "" {
+		return errors.New("HOSTCTL_REGION required for Google provider")
+	}
+
+	if p.project == "" {
+		return errors.New("GCLOUD_PROJECT required for Google provider")
+	}
+
+	httpClient, err := newOAuthClient(context.Background())
+	if err != nil {
+		return err
+	}
+
+	service, err := compute.New(httpClient)
+	if err != nil {
+		return err
+	}
+
+	p.service = service
+	return nil
+}
+
+func (p *googleCloudProvider) Env() *env.EnvSet {
+	readEnv()
+	return envSet
+}
+
+func (p *googleCloudProvider) Create(host providers.Host) error {
+	image, err := p.resolveAlias(host.Image)
+	if err != nil {
+		return err
+	}
+
+	instance := &compute.Instance{
+		Name:        host.Name,
+		MachineType: fmt.Sprintf("zones/%s/machineTypes/%s", host.Region, host.Flavor),
+		Disks: []*compute.AttachedDisk{{
+			// AutoDelete: true,
+			Boot: true,
+			InitializeParams: &compute.AttachedDiskInitializeParams{
+				SourceImage: image,
+			},
+		}},
+		NetworkInterfaces: []*compute.NetworkInterface{{
+			Network: "global/networks/default",
+			AccessConfigs: []*compute.AccessConfig{{
+				Type: "ONE_TO_ONE_NAT",
+			}},
+		}},
+	}
+
+	// TODO ssh key for host.Keyname
+
+	if host.Userdata != "" {
+		instance.Metadata = &compute.Metadata{
+			Items: []*compute.MetadataItems{
+				{Key: "user-data", Value: &host.Userdata},
+			},
+		}
+	}
+
+	op, err := p.service.Instances.Insert(p.project, p.region, instance).Do()
+
+	if err != nil {
+		return err
+	}
+
+	return p.waitForZoneOp(op)
+}
+
+func (p *googleCloudProvider) Destroy(name string) error {
+	op, err := p.service.Instances.Delete(p.project, p.region, name).Do()
+	if err != nil {
+		if err, ok := err.(*googleapi.Error); ok && err.Code == http.StatusNotFound {
+			return nil
+		}
+		return err
+	}
+	return p.waitForZoneOp(op)
+}
+
+func (p *googleCloudProvider) List(pattern string) (hosts []providers.Host) {
+	list, err := p.service.Instances.List(p.project, p.region).Do()
+	if err != nil {
+		return nil
+	}
+
+	for _, instance := range list.Items {
+		// TODO convert glob pattern into regex for server-side filtering?
+		if ok, _ := filepath.Match(pattern, instance.Name); ok {
+			// TODO filter hosts without a public IP?
+			hosts = append(hosts, providers.Host{
+				Name: instance.Name,
+			})
+		}
+	}
+
+	return hosts
+}
+
+func (p *googleCloudProvider) Get(name string) *providers.Host {
+	instance, err := p.service.Instances.Get(p.project, p.region, name).Do()
+	if err != nil {
+		return nil
+	}
+
+	for _, iface := range instance.NetworkInterfaces {
+		for _, access := range iface.AccessConfigs {
+			return &providers.Host{
+				Name: instance.Name,
+				IP:   access.NatIP,
+			}
+		}
+	}
+
+	return nil
+}
+
+func (p *googleCloudProvider) resolveAlias(image string) (string, error) {
+	// assume any image with a '/' is already full-qualified
+	if strings.ContainsRune(image, '/') {
+		return image, nil
+	}
+
+	alias, ok := PublicAliases[image]
+	// if there is no public alias, assume this is a valid image name within the project
+	if !ok {
+		return imagePath(p.project, image), nil
+	}
+
+	publicImageList, err := p.service.Images.List(alias.Project).Filter(fmt.Sprintf("name eq ^%s(-.+)*-v.+", alias.Name)).Do()
+	if err != nil {
+		return "", err
+	}
+
+	imageVersion := func(image *compute.Image) string {
+		parts := strings.Split(image.Name, "v")
+		return parts[len(parts)-1]
+	}
+
+	var publicImage *compute.Image
+	for _, image := range publicImageList.Items {
+		if image.Deprecated == nil && (publicImage == nil || imageVersion(image) > imageVersion(publicImage)) {
+			publicImage = image
+		}
+	}
+
+	if publicImage == nil {
+		return "", fmt.Errorf("could not find image for alias %s", image)
+	}
+
+	userImageList, err := p.service.Images.List(p.project).Filter(fmt.Sprintf("name eq ^%s$", image)).Do()
+	if err != nil {
+		return "", err
+	}
+
+	var userImage *compute.Image
+	for _, image := range userImageList.Items {
+		if image.Deprecated == nil {
+			userImage = image
+			break
+		}
+	}
+
+	if userImage == nil {
+		return publicImage.SelfLink, nil
+	}
+
+	return "", fmt.Errorf(`Image name "%s" is ambiguous, please use one of the fully-qualified names:
+Your image:
+    %s
+Public image:
+    %s
+`, image, imagePath(p.project, userImage.Name), imagePath(alias.Project, publicImage.Name))
+}
+
+func imagePath(project, name string) string {
+	return fmt.Sprintf("projects/%s/global/images/%s", project, name)
+}
+
+func (p *googleCloudProvider) waitForZoneOp(op *compute.Operation) (err error) {
+	opName := op.Name
+
+	for op.Status != "DONE" {
+		time.Sleep(1 * time.Second)
+
+		op, err = p.service.ZoneOperations.Get(p.project, p.region, opName).Do()
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func newOAuthClient(ctx context.Context) (*http.Client, error) {
+	var token *oauth2.Token
+
+	tokenJSON := envSet.Var("GCLOUD_OAUTH_TOKEN").Value.Get().(string)
+
+	if tokenJSON != "" {
+		token = new(oauth2.Token)
+		err := json.Unmarshal([]byte(tokenJSON), token)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		config, sdkErr := google.NewSDKConfig("")
+		if sdkErr == nil {
+			return config.Client(ctx), nil
+		}
+		fmt.Printf(`Unable to read "gcloud" authentication:
+    %s
+
+Attempting OAuth online authentication.
+
+For alternative authentication, please use:
+    gcloud auth login
+
+`, sdkErr)
+
+		token = tokenFromWeb(ctx, &defaultOAuthConfig)
+		saveToken(token)
+	}
+
+	return defaultOAuthConfig.Client(ctx, token), nil
+}
+
+func saveToken(token *oauth2.Token) {
+	path := "~/.hostctl"
+	fmt.Println("Success! Saving OAuth token to", path)
+
+	path, _ = homedir.Expand(path)
+	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0666)
+	if err != nil {
+		return
+	}
+	defer f.Close()
+
+	// if the file is not empty, make sure it ends with a newline
+	f.Seek(-1, os.SEEK_END)
+	buf := make([]byte, 1)
+	n, err := f.Read(buf)
+	if n == 0 {
+		if err != io.EOF {
+			return
+		}
+	} else if buf[0] != '\n' {
+		f.WriteString("\n")
+	}
+
+	tokenJSON, _ := json.Marshal(token)
+	fmt.Fprintf(f, "export GCLOUD_OAUTH_TOKEN='%s'\n", tokenJSON)
+}
+
+func tokenFromWeb(ctx context.Context, config *oauth2.Config) *oauth2.Token {
+	ch := make(chan string)
+	randState := fmt.Sprintf("st%d", time.Now().UnixNano())
+	ts := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		if req.URL.Path == "/favicon.ico" {
+			http.Error(rw, "", 404)
+			return
+		}
+		if req.FormValue("state") != randState {
+			http.Error(rw, "", 500)
+			return
+		}
+		if code := req.FormValue("code"); code != "" {
+			fmt.Fprintf(rw, "<h1>Success</h1>Authorized.")
+			rw.(http.Flusher).Flush()
+			ch <- code
+			return
+		}
+		http.Error(rw, "", 500)
+	}))
+	defer ts.Close()
+
+	config.RedirectURL = ts.URL
+	authURL := config.AuthCodeURL(randState)
+	go openURL(authURL)
+	fmt.Printf("Opening authentication at:\n    %s\n", authURL)
+	code := <-ch
+
+	token, err := config.Exchange(ctx, code)
+	if err != nil {
+		log.Fatalf("Token exchange error: %v", err)
+	}
+	return token
+}
+
+func openURL(url string) {
+	try := []string{"xdg-open", "google-chrome", "open"}
+	for _, bin := range try {
+		err := exec.Command(bin, url).Run()
+		if err == nil {
+			return
+		}
+	}
+}