Better handling of B2 authorization failures

This commit fixed 2 issues wrt Backblaze B2 authorization:
* every thread may call b2_authorize_account at the same time when there
are 401 errors
* if B2 has a login outage, then all threads will call b2_authorize_account
repeatedly without delay

A simple solution is to limit one b2_authorize_account call to once every
30 second regardless of how many threads there are.  If the call to
b2_authorize_account is not allowed, the random exponential backoff will
be performed.

src/duplicacy_b2client.go

@@ -62,6 +62,8 @@ type B2Client struct {
 	Threads            int
 	MaximumRetries     int
 	TestMode           bool
+
+	LastAuthorizationTime int64
 }
 
 // URL encode the given path but keep the slashes intact
@@ -253,8 +255,12 @@ func (client *B2Client) call(threadIndex int, requestURL string, method string,
 			if requestURL == B2AuthorizationURL {
 				return nil, nil, 0, fmt.Errorf("Authorization failure")
 			}
-			client.AuthorizeAccount(threadIndex)
+
+			// Attempt authorization again.  If authorization is actually not done, run the random backoff
+			_, allowed := client.AuthorizeAccount(threadIndex)
+			if allowed {
 				continue
+			}
 		} else if response.StatusCode == 403 {
 			if !client.TestMode {
 				return nil, nil, 0, fmt.Errorf("B2 cap exceeded")
@@ -291,13 +297,18 @@ type B2AuthorizeAccountOutput struct {
 	DownloadURL        string
 }
 
-func (client *B2Client) AuthorizeAccount(threadIndex int) (err error) {
+func (client *B2Client) AuthorizeAccount(threadIndex int) (err error, allowed bool) {
 	client.Lock.Lock()
 	defer client.Lock.Unlock()
 
+	// Don't authorize if the previous one was done less than 30 seconds ago
+	if client.LastAuthorizationTime != 0 && client.LastAuthorizationTime > time.Now().Unix() - 30 {
+		return nil, false
+	}
+
 	readCloser, _, _, err := client.call(threadIndex, B2AuthorizationURL, http.MethodPost, nil, make(map[string]string))
 	if err != nil {
-		return err
+		return err, true
 	}
 
 	defer readCloser.Close()
@@ -305,7 +316,7 @@ func (client *B2Client) AuthorizeAccount(threadIndex int) (err error) {
 	output := &B2AuthorizeAccountOutput{}
 
 	if err = json.NewDecoder(readCloser).Decode(&output); err != nil {
-		return err
+		return err, true
 	}
 
 	// The account id may be different from the application key id so we're getting the account id from the returned
@@ -317,7 +328,9 @@ func (client *B2Client) AuthorizeAccount(threadIndex int) (err error) {
 	client.DownloadURL = output.DownloadURL
 	client.IsAuthorized = true
 
-	return nil
+	client.LastAuthorizationTime = time.Now().Unix()
+
+	return nil, true
 }
 
 type ListBucketOutput struct {

src/duplicacy_b2client_test.go

@@ -50,7 +50,7 @@ func TestB2Client(t *testing.T) {
 
 	b2Client.TestMode = true
 
-	err := b2Client.AuthorizeAccount(0)
+	err, _ := b2Client.AuthorizeAccount(0)
 	if err != nil {
 		t.Errorf("Failed to authorize the b2 account: %v", err)
 		return

src/duplicacy_b2storage.go

@@ -19,7 +19,7 @@ func CreateB2Storage(accountID string, applicationKey string, bucket string, sto
 
 	client := NewB2Client(accountID, applicationKey, storageDir, threads)
 
-	err = client.AuthorizeAccount(0)
+	err, _ = client.AuthorizeAccount(0)
 	if err != nil {
 		return nil, err
 	}