Start message sender

[wolf4ood]

Feature Request

Currently as per state machine diagram, when a transfer process is in a SUSPENDED state either the consumer or the provider can send the start message for starting again the transfer process.
but in here only the provider is mentioned as the sender for the TransferStartMessage.

If the consumer is allowed to restart a transfer, in some scenario the provider, upon receiving a start message from the consumer, might need to transmit additional information about the restarted process like a new dataAddress. But I'm not sure if this is doable with the current state diagram

Which Areas Would Be Affected?

e.g., data offering, policy negotiation, data transfer, etc.

Type: normative / non-normative <-- please specify the affected scope

Why Is the Feature Desired?

Are there any requirements?

Solution Proposal

If possible, provide a (brief!) solution proposal.

[jimmarino]

Some notes:

The issue is that when there is a consumer pull transfer, it requires an access token sent from the provider, and the consumer suspends the transfer. In this case, if the consumer resumes, there is no way for the provider to send a new access token.

There are at least two ways to handle this:

1. Have the provider honor the old access token (originally sent when the transfer process was last started) or have a token refresh mechanism in the data plane.

2. Handling this in the control plane. This would require the provider to respond with an HTTP ACCEPTED when the consumer starts the transfer again, and send an async response message to the consumer with the token (the process of creating a token must be async and not a sync response to the consumer start request). This would require the definition of a new message type ("resume") and endpoint on the consumer.

I think we should select option 1 and not support 2 since the case of consumer pull, the consumer is in control of the data flow and can always pause receiving data directly in the data plane (i.e. pause a subscription or stop dequeuing messages).

[jimmarino]

Add best practices:

• Option 1
• Provider may need to terminate and restart