def format_stdin_to_stdout(
    fast: bool,
    *,
    content: Optional[str] = None,
    write_back: WriteBack = WriteBack.NO,
    mode: Mode,
    lines: Collection[tuple[int, int]] = (),
) -> bool:
    """Format file on stdin. Return True if changed.

    If content is None, it's read from sys.stdin.

    If `write_back` is YES, write reformatted code back to stdout. If it is DIFF,
    write a diff to stdout. The `mode` argument is passed to
    :func:`format_file_contents`.
    """
    then = datetime.now(timezone.utc)

    if content is None:
        src, encoding, newline = decode_bytes(sys.stdin.buffer.read())
    else:
        src, encoding, newline = content, "utf-8", ""

    dst = src
    try:
        dst = format_file_contents(src, fast=fast, mode=mode, lines=lines)
        return True

    except NothingChanged:
        return False

    finally:
        f = io.TextIOWrapper(
            sys.stdout.buffer, encoding=encoding, newline=newline, write_through=True
        )
        if write_back == WriteBack.YES:
            # Make sure there's a newline after the content
            if dst and dst[-1] != "\n":
                dst += "\n"
            f.write(dst)
        elif write_back in (WriteBack.DIFF, WriteBack.COLOR_DIFF):
            now = datetime.now(timezone.utc)
            src_name = f"STDIN\t{then}"
            dst_name = f"STDOUT\t{now}"
            d = diff(src, dst, src_name, dst_name)
            if write_back == WriteBack.COLOR_DIFF:
                d = color_diff(d)
                f = wrap_stream_for_windows(f)
            f.write(d)
        f.detach()
Format file on stdin. Return True if changed.

    If content is None, it's read from sys.stdin.

    If `write_back` is YES, write reformatted code back to stdout. If it is DIFF,
    write a diff to stdout. The `mode` argument is passed to
    :func:`format_file_contents`.
    
src/black/__init__.py