Add an example sending chunked responses

[mfelsche]

FYI @redvers

Let me know if this example addresses your problem.

[redvers]

The issue as I understand it is that finished() is called by actor _ServerConnection here:

  be _receive_finished(request_id: RequestID) =>
    """
    Indicates that the last *inbound* body chunk has been sent to
    `_chunk`. This is passed on to the back end.
    """
    _backend.finished(request_id)

In your example, (Line 211-212):

    while true do
      let file_chunk = file.read(chunk_size)

All the Array[U8 val] iso's that you create will be new allocations and will never have any opportunity to be available for Garbage Collection until:

a. The loop has completed (In other words, the entire size of the file has to have been fully allocated to memory).
b. The _receive_finished() behaviour has terminated.

I don't think it solves the problem, as it still results in at least 4.7G of memory allocation for a 4.7G .iso file.

[redvers]

After receiving the completed request, we need to send the chunks across multiple behaviours to allow for GC to happen.

[mfelsche]

I solved that issue by delegating the actual file reading and sending to another actor

[jemc]

We discussed this on the sync call. The basic outlook here is that both Sean and Red would like to see a refactored API for this library in the future, but Red says that for now this PR is good documentation of the API that currently exists, and it makes sense to merge.