Fix race condition in gcp auth provider plugin

plugin/pkg/client/auth/gcp/gcp.go

@@ -23,6 +23,7 @@ import (
 	"net/http"
 	"os/exec"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/golang/glog"
@@ -74,6 +75,7 @@ func (g *gcpAuthProvider) WrapTransport(rt http.RoundTripper) http.RoundTripper
 func (g *gcpAuthProvider) Login() error { return nil }
 
 type cachedTokenSource struct {
+	lk          sync.Mutex
 	source      oauth2.TokenSource
 	accessToken string
 	expiry      time.Time
@@ -99,11 +101,7 @@ func newCachedTokenSource(accessToken, expiry string, persister restclient.AuthP
 }
 
 func (t *cachedTokenSource) Token() (*oauth2.Token, error) {
-	tok := &oauth2.Token{
-		AccessToken: t.accessToken,
-		TokenType:   "Bearer",
-		Expiry:      t.expiry,
-	}
+	tok := t.cachedToken()
 	if tok.Valid() && !tok.Expiry.IsZero() {
 		return tok, nil
 	}
@@ -111,16 +109,39 @@ func (t *cachedTokenSource) Token() (*oauth2.Token, error) {
 	if err != nil {
 		return nil, err
 	}
+	cache := t.update(tok)
 	if t.persister != nil {
-		t.cache["access-token"] = tok.AccessToken
-		t.cache["expiry"] = tok.Expiry.Format(time.RFC3339Nano)
-		if err := t.persister.Persist(t.cache); err != nil {
+		if err := t.persister.Persist(cache); err != nil {
 			glog.V(4).Infof("Failed to persist token: %v", err)
 		}
 	}
 	return tok, nil
 }
 
+func (t *cachedTokenSource) cachedToken() *oauth2.Token {
+	t.lk.Lock()
+	defer t.lk.Unlock()
+	return &oauth2.Token{
+		AccessToken: t.accessToken,
+		TokenType:   "Bearer",
+		Expiry:      t.expiry,
+	}
+}
+
+func (t *cachedTokenSource) update(tok *oauth2.Token) map[string]string {
+	t.lk.Lock()
+	defer t.lk.Unlock()
+	t.accessToken = tok.AccessToken
+	t.expiry = tok.Expiry
+	ret := map[string]string{}
+	for k, v := range t.cache {
+		ret[k] = v
+	}
+	ret["access-token"] = t.accessToken
+	ret["expiry"] = t.expiry.Format(time.RFC3339Nano)
+	return ret
+}
+
 type commandTokenSource struct {
 	cmd       string
 	args      []string

plugin/pkg/client/auth/gcp/gcp_test.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"reflect"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -141,3 +142,70 @@ func TestCmdTokenSource(t *testing.T) {
 		}
 	}
 }
+
+type fakePersister struct {
+	lk    sync.Mutex
+	cache map[string]string
+}
+
+func (f *fakePersister) Persist(cache map[string]string) error {
+	f.lk.Lock()
+	defer f.lk.Unlock()
+	f.cache = map[string]string{}
+	for k, v := range cache {
+		f.cache[k] = v
+	}
+	return nil
+}
+
+func (f *fakePersister) read() map[string]string {
+	ret := map[string]string{}
+	f.lk.Lock()
+	for k, v := range f.cache {
+		ret[k] = v
+	}
+	return ret
+}
+
+type fakeTokenSource struct {
+	token *oauth2.Token
+	err   error
+}
+
+func (f *fakeTokenSource) Token() (*oauth2.Token, error) {
+	return f.token, f.err
+}
+
+func TestCachedTokenSource(t *testing.T) {
+	tok := &oauth2.Token{AccessToken: "fakeaccesstoken"}
+	persister := &fakePersister{}
+	source := &fakeTokenSource{
+		token: tok,
+		err:   nil,
+	}
+	cache := map[string]string{
+		"foo": "bar",
+		"baz": "bazinga",
+	}
+	ts, err := newCachedTokenSource("fakeaccesstoken", "", persister, source, cache)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var wg sync.WaitGroup
+	wg.Add(10)
+	for i := 0; i < 10; i++ {
+		go func() {
+			_, err := ts.Token()
+			if err != nil {
+				t.Errorf("unexpected error: %s", err)
+			}
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+	cache["access-token"] = "fakeaccesstoken"
+	cache["expiry"] = tok.Expiry.Format(time.RFC3339Nano)
+	if got := persister.read(); !reflect.DeepEqual(got, cache) {
+		t.Errorf("got cache %v, want %v", got, cache)
+	}
+}