oauth2: rewrite google package, fix the broken build

Change-Id: I2753a88d7be483bdbc0cac09a1beccc4806ea4bc
Reviewed-on: https://go-review.googlesource.com/1361
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

google/appengine.go

@@ -7,108 +7,31 @@
 package google
 
 import (
-	"net/http"
-	"strings"
-	"sync"
 	"time"
 
-	"golang.org/x/oauth2"
-
 	"appengine"
-	"appengine/memcache"
-	"appengine/urlfetch"
+
+	"golang.org/x/oauth2"
 )
 
-var (
-	// memcacheGob enables mocking of the memcache.Gob calls for unit testing.
-	memcacheGob memcacher = &aeMemcache{}
-
-	// accessTokenFunc enables mocking of the appengine.AccessToken call for unit testing.
-	accessTokenFunc = appengine.AccessToken
-
-	// mu protects multiple threads from attempting to fetch a token at the same time.
-	mu sync.Mutex
-
-	// tokens implements a local cache of tokens to prevent hitting quota limits for appengine.AccessToken calls.
-	tokens map[string]*oauth2.Token
-)
-
-// safetyMargin is used to avoid clock-skew problems.
-// 5 minutes is conservative because tokens are valid for 60 minutes.
-const safetyMargin = 5 * time.Minute
-
-func init() {
-	tokens = make(map[string]*oauth2.Token)
-}
-
-// AppEngineContext requires an App Engine request context.
-func AppEngineContext(ctx appengine.Context) oauth2.Option {
-	return func(opts *oauth2.Options) error {
-		opts.TokenFetcherFunc = makeAppEngineTokenFetcher(ctx, opts)
-		opts.Client = &http.Client{
-			Transport: &urlfetch.Transport{Context: ctx},
-		}
-		return nil
+// AppEngineTokenSource returns a token source that fetches tokens
+// issued to the current App Engine application's service account.
+// If you are implementing a 3-legged OAuth 2.0 flow on App Engine
+// that involves user accounts, see oauth2.Config instead.
+//
+// You are required to provide a valid appengine.Context as context.
+func AppEngineTokenSource(ctx appengine.Context, scope ...string) oauth2.TokenSource {
+	return &appEngineTokenSource{
+		ctx:         ctx,
+		scopes:      scope,
+		fetcherFunc: aeFetcherFunc,
 	}
 }
 
-// FetchToken fetches a new access token for the provided scopes.
-// Tokens are cached locally and also with Memcache so that the app can scale
-// without hitting quota limits by calling appengine.AccessToken too frequently.
-func makeAppEngineTokenFetcher(ctx appengine.Context, opts *oauth2.Options) func(*oauth2.Token) (*oauth2.Token, error) {
-	return func(existing *oauth2.Token) (*oauth2.Token, error) {
-		mu.Lock()
-		defer mu.Unlock()
-
-		key := ":" + strings.Join(opts.Scopes, "_")
-		now := time.Now().Add(safetyMargin)
-		if t, ok := tokens[key]; ok && !t.Expiry.Before(now) {
-			return t, nil
-		}
-		delete(tokens, key)
-
-		// Attempt to get token from Memcache
-		tok := new(oauth2.Token)
-		_, err := memcacheGob.Get(ctx, key, tok)
-		if err == nil && !tok.Expiry.Before(now) {
-			tokens[key] = tok // Save token locally
-			return tok, nil
-		}
-
-		token, expiry, err := accessTokenFunc(ctx, opts.Scopes...)
-		if err != nil {
-			return nil, err
-		}
-		t := &oauth2.Token{
-			AccessToken: token,
-			Expiry:      expiry,
-		}
-		tokens[key] = t
-		// Also back up token in Memcache
-		if err = memcacheGob.Set(ctx, &memcache.Item{
-			Key:        key,
-			Value:      []byte{},
-			Object:     *t,
-			Expiration: expiry.Sub(now),
-		}); err != nil {
-			ctx.Errorf("unexpected memcache.Set error: %v", err)
-		}
-		return t, nil
+var aeFetcherFunc = func(ctx oauth2.Context, scope ...string) (string, time.Time, error) {
+	c, ok := ctx.(appengine.Context)
+	if !ok {
+		return "", time.Time{}, errInvalidContext
 	}
-}
-
-// aeMemcache wraps the needed Memcache functionality to make it easy to mock
-type aeMemcache struct{}
-
-func (m *aeMemcache) Get(c appengine.Context, key string, tok *oauth2.Token) (*memcache.Item, error) {
-	return memcache.Gob.Get(c, key, tok)
-}
-
-func (m *aeMemcache) Set(c appengine.Context, item *memcache.Item) error {
-	return memcache.Gob.Set(c, item)
-}
-
-type memcacher interface {
-	Get(c appengine.Context, key string, tok *oauth2.Token) (*memcache.Item, error)
-	Set(c appengine.Context, item *memcache.Item) error
+	return appengine.AccessToken(c, scope...)
 }