Fix index out of bounds panic for Retry-After header (jomei#122)

* fix index out of bounds * RateLimitedError

Author: dxaviud

client.go

@@ -142,10 +142,15 @@ func (c *Client) request(ctx context.Context, method string, urlStr string, quer
 
 failedAttempts++
 if failedAttempts == c.maxRetries {
-return nil, fmt.Errorf("Retry request with 429 response failed after %d retries", failedAttempts)
+return nil, &RateLimitedError{Message: fmt.Sprintf("Retry request with 429 response failed after %d retries", failedAttempts)}
 }
 // https://developers.notion.com/reference/request-limits#rate-limits
-retryAfter := res.Header["Retry-After"][0]
+retryAfterHeader := res.Header["Retry-After"]
+if len(retryAfterHeader) == 0 {
+return nil, &RateLimitedError{Message: "Retry-After header missing from Notion API response headers for 429 response"}
+}
+retryAfter := retryAfterHeader[0]
+
 waitSeconds, err := strconv.Atoi(retryAfter)
 if err != nil {
 break // should not happen

error.go

@@ -12,3 +12,11 @@ type Error struct {
 func (e *Error) Error() string {
 return e.Message
 }
+
+type RateLimitedError struct {
+Message string
+}
+
+func (e *RateLimitedError) Error() string {
+return e.Message
+}