[2.6.x] Missing the equivalent of onDoneEnumerating/onRequestCompletion hook for HttpEntity.Strict result body

[FranklinYinanDing]

Play Version (2.5.x / etc)

2.6.x

API (Scala / Java / Neither / Both)

Both

Expected Behavior

Please describe the expected behavior of the issue, starting from the first action.

1. HttpEntity.Strict result body should provide something similar to onDoneEnumerating/onRequestCompletion hook for the approximate timing of last-byte-sent.

Actual Behavior

1. Based on our discussion, the only way to achieve the goal is to convert Strict to Streamed, then use watchTermination hook on the Source.

First, this approach changes the type, and could lead to some issues, if any logic is expecting Strict body but don't know some filter converts it to Streamed type.
And also, the converting introduces some overhead for stream materialization.