resolver: avoid error caching on token fetch

util/resolver/authorizer.go

@@ -220,15 +220,13 @@ func (a *dockerAuthorizer) AddResponses(ctx context.Context, responses []*http.R
 
 // authResult is used to control limit rate.
 type authResult struct {
-	sync.WaitGroup
 	token   string
-	err     error
 	expires time.Time
 }
 
 // authHandler is used to handle auth request per registry server.
 type authHandler struct {
-	sync.Mutex
+	g flightcontrol.Group
 
 	client *http.Client
 
@@ -240,7 +238,8 @@ type authHandler struct {
 
 	// scopedTokens caches token indexed by scopes, which used in
 	// bearer auth case
-	scopedTokens map[string]*authResult
+	scopedTokens   map[string]*authResult
+	scopedTokensMu sync.Mutex
 
 	lastUsed time.Time
 
@@ -292,54 +291,51 @@ func (ah *authHandler) doBearerAuth(ctx context.Context, sm *session.Manager, g
 	// Docs: https://docs.docker.com/registry/spec/auth/scope
 	scoped := strings.Join(to.Scopes, " ")
 
-	ah.Lock()
-	for {
+	res, err := ah.g.Do(ctx, scoped, func(ctx context.Context) (interface{}, error) {
+		ah.scopedTokensMu.Lock()
 		r, exist := ah.scopedTokens[scoped]
-		if !exist {
-			// no entry cached
-			break
-		}
-		ah.Unlock()
-		r.Wait()
-		if r.err != nil {
-			select {
-			case <-ctx.Done():
-				return "", r.err
-			default:
+		ah.scopedTokensMu.Unlock()
+		if exist {
+			if r.expires.IsZero() || r.expires.After(time.Now()) {
+				return r, nil
 			}
 		}
-		if !errors.Is(r.err, context.Canceled) &&
-			(r.expires.IsZero() || r.expires.After(time.Now())) {
-			return r.token, r.err
-		}
-		// r.err is canceled or token expired. Get rid of it and try again
-		ah.Lock()
-		r2, exist := ah.scopedTokens[scoped]
-		if exist && r == r2 {
-			delete(ah.scopedTokens, scoped)
+		r, err := ah.fetchToken(ctx, sm, g, to)
+		if err != nil {
+			return nil, err
 		}
+		ah.scopedTokensMu.Lock()
+		ah.scopedTokens[scoped] = r
+		ah.scopedTokensMu.Unlock()
+		return r, nil
+	})
+
+	if err != nil || res == nil {
+		return "", err
 	}
+	r := res.(*authResult)
+	if r == nil {
+		return "", nil
+	}
+	return r.token, nil
+}
 
-	// only one fetch token job
-	r := new(authResult)
-	r.Add(1)
-	ah.scopedTokens[scoped] = r
-	ah.Unlock()
-
+func (ah *authHandler) fetchToken(ctx context.Context, sm *session.Manager, g session.Group, to auth.TokenOptions) (r *authResult, err error) {
 	var issuedAt time.Time
 	var expires int
+	var token string
 	defer func() {
 		token = fmt.Sprintf("Bearer %s", token)
-		r.token, r.err = token, err
+
 		if err == nil {
+			r = &authResult{token: token}
 			if issuedAt.IsZero() {
 				issuedAt = time.Now()
 			}
 			if exp := issuedAt.Add(time.Duration(float64(expires)*0.9) * time.Second); time.Now().Before(exp) {
 				r.expires = exp
 			}
 		}
-		r.Done()
 	}()
 
 	if ah.authority != nil {
@@ -351,10 +347,11 @@ func (ah *authHandler) doBearerAuth(ctx context.Context, sm *session.Manager, g
 			Scopes:   to.Scopes,
 		}, sm, g)
 		if err != nil {
-			return "", err
+			return nil, err
 		}
 		issuedAt, expires = time.Unix(resp.IssuedAt, 0), int(resp.ExpiresIn)
-		return resp.Token, nil
+		token = resp.Token
+		return nil, nil
 	}
 
 	// fetch token for the resource scope
@@ -374,29 +371,32 @@ func (ah *authHandler) doBearerAuth(ctx context.Context, sm *session.Manager, g
 				if (errStatus.StatusCode == 405 && to.Username != "") || errStatus.StatusCode == 404 || errStatus.StatusCode == 401 {
 					resp, err := auth.FetchTokenWithOAuth(ctx, ah.client, nil, "buildkit-client", to)
 					if err != nil {
-						return "", err
+						return nil, err
 					}
 					issuedAt, expires = resp.IssuedAt, resp.ExpiresIn
-					return resp.AccessToken, nil
+					token = resp.AccessToken
+					return nil, nil
 				}
 				log.G(ctx).WithFields(logrus.Fields{
 					"status": errStatus.Status,
 					"body":   string(errStatus.Body),
 				}).Debugf("token request failed")
 			}
-			return "", err
+			return nil, err
 		}
 		issuedAt, expires = resp.IssuedAt, resp.ExpiresIn
-		return resp.Token, nil
+		token = resp.Token
+		return nil, nil
 	}
 	// do request anonymously
 	resp, err := auth.FetchToken(ctx, ah.client, nil, to)
 	if err != nil {
-		return "", errors.Wrap(err, "failed to fetch anonymous token")
+		return nil, errors.Wrap(err, "failed to fetch anonymous token")
 	}
 	issuedAt, expires = resp.IssuedAt, resp.ExpiresIn
 
-	return resp.Token, nil
+	token = resp.Token
+	return nil, nil
 }
 
 func invalidAuthorization(c auth.Challenge, responses []*http.Response) error {