EasyAwscr::S3::Internals::ChunkedIO::Handler

Will be called once after the last write operation.

Will be called once before the first write operation.

Can be called multiple times. The input is the current chunk. The implementer can either process it synchronously or asynchronously. Optionally, the function can return a buffer (either the input buffer or another buffer of equal size) that the ChunkedIO class can reuse. However, it is always safe to return nil and let the class reallocate a new buffer instead.