Collate a string representation of root into a single string.

This is basically gluing flatten to an io.BytesIO and returning the results. See flatten for the exact meanings of request and root.

ReturnsA Deferred which will be called back with a single string as its result when root has been completely flattened into write or which will be errbacked if an unexpected exception occurs.
API Documentation for Twisted, generated by pydoctor at 2017-09-23 19:45:03.