Build .conda packages with conda-package-streaming

build.py

@contextmanager
def builder(
    destination, file_id, is_info=lambda filename: filename.startswith("info/")
):
    """
    Yield TarFile object for adding files, then transmute to "{destination}/{file_id}.conda"
    """
    # Stream through a pipe instead of collecting all data in a temporary
    # tarfile. Underlying transmute_stream collects data into separate pkg, info
    # tar to be able to send complete size to zstd, so this strategy avoids one
    # temporary file but not all of them. Compare to conda-package-handling 2.3
    # which uses less temporary space but reads every input file twice; once to
    # count the size and a second time to stream into a zstd compressor.
    r, w = os.pipe()
    with open(r, mode="rb") as reader, open(w, mode="wb") as writer:

        def transmute_thread():
            with tarfile.open(fileobj=reader, mode="r|") as tar:
                transmute_stream(
                    file_id,
                    destination,
                    package_stream=((tar, entry) for entry in tar),
                    is_info=is_info,
                )

        t = threading.Thread(target=transmute_thread)
        t.start()

        with tarfile.open(fileobj=writer, mode="w|") as tar:
            yield tar

        t.join()