When a Docker container with the same name already exists (e.g., from a
previous crashed GNS3 session), Docker returns a 409 Conflict error
when trying to create a new container with that name. This causes the
project open operation to fail.
This fix adds automatic cleanup of stale containers when encountering
a name conflict:
- Added DockerHttp409Error exception class
- Updated http_query to detect 409 status codes
- Modified create() to remove conflicting containers and retry
Fixes the issue where opening a project fails with:
"Docker has returned an error: 409 Conflict. The container name
'/GNS3.xxx' is already in use by container 'xxx'"
