[MESOS-6568] JSON serialization should not omit empty arrays in HTTP APIs

• Type: Improvement
• Status: Reviewable
• Priority: Major
• Resolution: Unresolved
• Component/s: HTTP API
• Labels: mesosphere
• Epic Link: Operator API v1 Improvements
• Sprint: Studio 4: RI-21 61, Studio 4: RI-22 62, Studio 4: RI-22 63, Studio 4: RI-23 64
• Story Points: 3
• Assignee: Benjamin Mahler
• Reporter: Neil Conway
• Created: 09/Nov/16 20:45
• Updated: 22/Apr/20 17:12

Description

When using the JSON content type with the HTTP APIs, a repeated protobuf field is omitted entirely from the JSON serialization of the message. For example, this is a response to the GetTasks call:

{
  "get_tasks": {
    "tasks": [{...}]
  },
  "type": "GET_TASKS"
}

I think it would be better to include empty arrays for the other fields of the message (pending_tasks, completed_tasks, etc.). Advantages:

1. Consistency with the old HTTP endpoints, e.g., /state
2. Semantically, an empty array is more accurate. The master's response should be interpreted as saying it doesn't know about any pending/completed tasks; that is more accurately conveyed by explicitly including an empty array, not by omitting the key entirely.

NOTE: The asV1Protobuf copy needs to also be updated.

Issue Links

• relates to: MESOS-9896 Consider using protobuf provided json conversion facilities rather than custom ones.