feat: retry request on API timeout error (#797)

This error code explicitly document that the request should be retried.

Author: jooola

hcloud/client_handler_retry.go

@@ -66,6 +66,8 @@ func retryPolicy(resp *Response, err error) bool {
 				return true
 			case ErrorCodeRateLimitExceeded:
 				return true
+			case ErrorCodeTimeout:
+				return true
 			}
 		case errors.Is(err, ErrStatusCode):
 			switch resp.Response.StatusCode {

hcloud/client_handler_retry_test.go

@@ -130,6 +130,11 @@ func TestRetryPolicy(t *testing.T) {
 			resp: fakeResponse(t, 503, ``, false),
 			want: false,
 		},
+		{
+			name: "server returns timeout error",
+			resp: fakeResponse(t, 504, `{"error":{"code":"timeout"}}`, true),
+			want: true,
+		},
 		{
 			name: "api returns rate_limit_exceeded error",
 			resp: fakeResponse(t, 429, `{"error":{"code":"rate_limit_exceeded"}}`, true),

hcloud/hcloud.go

@@ -24,6 +24,7 @@ When the API returned an HTTP error, with the status code:
 When the API returned an application error, with the code:
   - [ErrorCodeConflict]
   - [ErrorCodeRateLimitExceeded]
+  - [ErrorCodeTimeout]
 
 Changes to the retry policy might occur between releases, and will not be considered
 breaking changes.