fix: stop the blind backoff from growing after timed retries

internal/httpclient/httpclient.go

@@ -74,6 +74,8 @@ func (c *Client) Get(url string, headers map[string]string) ([]byte, error) {
 // GetWithContext is Get with a context. The request and the waits between
 // retries stop when ctx is cancelled or reaches its deadline.
 func (c *Client) GetWithContext(ctx context.Context, url string, headers map[string]string) ([]byte, error) {
+	blind := 0
+
 	for attempt := 1; ; attempt++ {
 		resp, err := c.do(ctx, url, headers)
 		if err != nil {
@@ -87,13 +89,14 @@ func (c *Client) GetWithContext(ctx context.Context, url string, headers map[str
 
 		_ = resp.Body.Close()
 
-		limit := maxAttempts
+		// The backoff doubles per blind retry, not per attempt: retries
+		// where the server gave a time must not inflate it.
 		if !told {
-			limit = maxBlindAttempts
-			wait = time.Minute << (attempt - 1)
+			blind++
+			wait = time.Minute << (blind - 1)
 		}
 
-		if attempt == limit {
+		if attempt >= maxAttempts || blind >= maxBlindAttempts {
 			return nil, fmt.Errorf("%w after %d attempts: %s", ErrRateLimited, attempt, resp.Status)
 		}
 

internal/httpclient/httpclient_test.go

@@ -361,3 +361,28 @@ func TestGetWithContextCancelInterruptsBackoff(t *testing.T) {
 		t.Errorf("cancel did not interrupt backoff: elapsed %v", elapsed)
 	}
 }
+
+func TestGetCountsBlindRetriesOnTheirOwn(t *testing.T) {
+	steps := []step{
+		{status: http.StatusTooManyRequests, retryAfter: "1"},
+		{status: http.StatusTooManyRequests, retryAfter: "1"},
+		{status: http.StatusTooManyRequests, retryAfter: "1"},
+		{status: http.StatusTooManyRequests, retryAfter: "1"},
+	}
+	for range maxBlindAttempts {
+		steps = append(steps, step{status: http.StatusTooManyRequests})
+	}
+	c, url, waits := newClient(t, steps...)
+
+	_, err := c.Get(url, nil)
+	if !errors.Is(err, ErrRateLimited) {
+		t.Errorf("err = %v, want ErrRateLimited", err)
+	}
+	want := []time.Duration{
+		time.Second, time.Second, time.Second, time.Second,
+		time.Minute, 2 * time.Minute, 4 * time.Minute,
+	}
+	if !slices.Equal(*waits, want) {
+		t.Errorf("waits = %v, want %v", *waits, want)
+	}
+}