Separate retry backoff calculation from retry scheduling

[jbelkins]

Describe the feature

Smithy Reference Architecture defines the RetryBackoffStrategy type, which (translated to Swift) is:

public protocol RetryBackoffStrategy {
    func computeNextBackoffDelay(attempt: Int) -> TimeInterval
}

Calling the computeNextBackoffDelay(attempt:) method on this protocol allows a client to determine the delay to wait before performing a retry. The client can then use this delay to schedule retry using the scheduling mechanism and HTTP client of their choice.

Looking at the CRT implementation of retry, aws-c-io does not expose such a method, even though it does calculate the needed delay internally. Instead, it appears that the C function aws_retry_strategy_schedule_retry is provided, which calculates the delay and schedules the retry, after the appropriate delay, on CRT's own event loop. (aws-crt-swift uses this C method in its scheduleRetry(token:errorType:) method for its own public retry interface.)

Please provide methods for determining retry backoff delay separate from the methods for scheduling retry; this will assist with compliance with the Smithy Reference Architecture and with future modularization work on the AWS SDK for Swift.

Use Case

Allows for use of CRT's retry backoff logic with non-CRT HTTP clients.

Proposed Solution

No response

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

[epau]

Blocked: Needs more information on exactly what is required.

[jbelkins]

This feature is implemented in smithy-swift and further CRT support for retry is not required. Closing.

[github-actions]

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