Resume after shutdown always fetch last interrupted message again

[chingkamhing]

Condition:

• pub/sub provider use redis
• use message router to handle all the message handler
• publish 10 messages
• handler function takes 5 seconds to process
• Ctrl+C the pubsub server after successfully processed first message
• during shutdown, 1 pending message (e.g. msg 2) is successfully processed (i.e. returned nil error in handler)
• pubsub server finished shutdown after the pending message is handled
• restart pubsub server, success to resume process the rest of the messages

Problem

• although the pending message (i.e. msg 2) was processed successfully before shutdown, the same message is fetched again after resume (i.e. msg 2 is incorrectly processed twice)

Attempts to fix but the problem still the same:

• tried to increase the message.RouterConfig CloseTimeout to something like 30s
• tried manually acknowledge the message in handler

Question:
Just wonder how to avoid the successfully handled message from being fetched again after resume? Did I miss any setting?

Thanks,
Kam Ching