Introduce an option function type
- Reduce the duplicate code by merging the flows and determining the flow type by looking at the provided options. - Options as a function type allows us to validate an individual an option in its scope and makes it easier to compose the built-in options with the third-party ones.
This commit is contained in:
Burcu Dogan
@@ -7,7 +7,6 @@
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package google
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import (
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"net/http"
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"strings"
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"sync"
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"time"
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@@ -19,6 +18,82 @@ import (
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"appengine/urlfetch"
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)
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var (
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// memcacheGob enables mocking of the memcache.Gob calls for unit testing.
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memcacheGob memcacher = &aeMemcache{}
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// accessTokenFunc enables mocking of the appengine.AccessToken call for unit testing.
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accessTokenFunc = appengine.AccessToken
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// mu protects multiple threads from attempting to fetch a token at the same time.
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mu sync.Mutex
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// tokens implements a local cache of tokens to prevent hitting quota limits for appengine.AccessToken calls.
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tokens map[string]*oauth2.Token
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)
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// safetyMargin is used to avoid clock-skew problems.
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// 5 minutes is conservative because tokens are valid for 60 minutes.
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const safetyMargin = 5 * time.Minute
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func init() {
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tokens = make(map[string]*oauth2.Token)
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}
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// AppEngineContext requires an App Engine request context.
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func AppEngineContext(ctx appengine.Context) oauth2.Option {
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return func(opts *oauth2.Options) error {
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opts.TokenFetcherFunc = makeAppEngineTokenFetcher(ctx, opts)
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opts.Transport = &urlfetch.Transport{Context: ctx}
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return nil
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}
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}
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// FetchToken fetches a new access token for the provided scopes.
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// Tokens are cached locally and also with Memcache so that the app can scale
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// without hitting quota limits by calling appengine.AccessToken too frequently.
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func makeAppEngineTokenFetcher(ctx appengine.Context, opts *oauth2.Options) func(*oauth2.Token) (*oauth2.Token, error) {
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return func(existing *oauth2.Token) (*oauth2.Token, error) {
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mu.Lock()
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defer mu.Unlock()
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key := ":" + strings.Join(opts.Scopes, "_")
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now := time.Now().Add(safetyMargin)
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if t, ok := tokens[key]; ok && !t.Expiry.Before(now) {
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return t, nil
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}
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delete(tokens, key)
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// Attempt to get token from Memcache
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tok := new(oauth2.Token)
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_, err := memcacheGob.Get(ctx, key, tok)
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if err == nil && !tok.Expiry.Before(now) {
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tokens[key] = tok // Save token locally
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return tok, nil
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}
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token, expiry, err := accessTokenFunc(ctx, opts.Scopes...)
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if err != nil {
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return nil, err
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}
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t := &oauth2.Token{
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AccessToken: token,
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Expiry: expiry,
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}
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tokens[key] = t
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// Also back up token in Memcache
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if err = memcacheGob.Set(ctx, &memcache.Item{
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Key: key,
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Value: []byte{},
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Object: *t,
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Expiration: expiry.Sub(now),
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}); err != nil {
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ctx.Errorf("unexpected memcache.Set error: %v", err)
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}
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return t, nil
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}
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}
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// aeMemcache wraps the needed Memcache functionality to make it easy to mock
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type aeMemcache struct{}
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@@ -34,99 +109,3 @@ type memcacher interface {
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Get(c appengine.Context, key string, tok *oauth2.Token) (*memcache.Item, error)
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Set(c appengine.Context, item *memcache.Item) error
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}
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// memcacheGob enables mocking of the memcache.Gob calls for unit testing.
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var memcacheGob memcacher = &aeMemcache{}
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// accessTokenFunc enables mocking of the appengine.AccessToken call for unit testing.
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var accessTokenFunc = appengine.AccessToken
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// safetyMargin is used to avoid clock-skew problems.
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// 5 minutes is conservative because tokens are valid for 60 minutes.
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const safetyMargin = 5 * time.Minute
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// mu protects multiple threads from attempting to fetch a token at the same time.
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var mu sync.Mutex
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// tokens implements a local cache of tokens to prevent hitting quota limits for appengine.AccessToken calls.
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var tokens map[string]*oauth2.Token
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func init() {
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tokens = make(map[string]*oauth2.Token)
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}
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// AppEngineConfig represents a configuration for an
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// App Engine application's Google service account.
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type AppEngineConfig struct {
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// Transport is the http.RoundTripper to be used
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// to construct new oauth2.Transport instances from
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// this configuration.
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Transport http.RoundTripper
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context appengine.Context
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scopes []string
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}
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// NewAppEngineConfig creates a new AppEngineConfig for the
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// provided auth scopes.
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func NewAppEngineConfig(context appengine.Context, scopes ...string) *AppEngineConfig {
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return &AppEngineConfig{
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context: context,
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scopes: scopes,
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}
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}
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// NewTransport returns a transport that authorizes
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// the requests with the application's service account.
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func (c *AppEngineConfig) NewTransport() *oauth2.Transport {
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return oauth2.NewTransport(c.transport(), c, nil)
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}
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// FetchToken fetches a new access token for the provided scopes.
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// Tokens are cached locally and also with Memcache so that the app can scale
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// without hitting quota limits by calling appengine.AccessToken too frequently.
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func (c *AppEngineConfig) FetchToken(existing *oauth2.Token) (*oauth2.Token, error) {
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mu.Lock()
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defer mu.Unlock()
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key := ":" + strings.Join(c.scopes, "_")
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now := time.Now().Add(safetyMargin)
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if t, ok := tokens[key]; ok && !t.Expiry.Before(now) {
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return t, nil
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}
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delete(tokens, key)
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// Attempt to get token from Memcache
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tok := new(oauth2.Token)
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_, err := memcacheGob.Get(c.context, key, tok)
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if err == nil && !tok.Expiry.Before(now) {
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tokens[key] = tok // Save token locally
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return tok, nil
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}
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token, expiry, err := accessTokenFunc(c.context, c.scopes...)
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if err != nil {
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return nil, err
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}
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t := &oauth2.Token{
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AccessToken: token,
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Expiry: expiry,
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}
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tokens[key] = t
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// Also back up token in Memcache
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if err = memcacheGob.Set(c.context, &memcache.Item{
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Key: key,
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Value: []byte{},
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Object: *t,
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Expiration: expiry.Sub(now),
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}); err != nil {
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c.context.Errorf("unexpected memcache.Set error: %v", err)
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}
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return t, nil
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}
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func (c *AppEngineConfig) transport() http.RoundTripper {
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if c.Transport != nil {
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return c.Transport
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}
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return &urlfetch.Transport{Context: c.context}
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}
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