s3io.py

import io


class S3IO(io.BufferedIOBase):
    def __init__(self, s3_obj):
        self.obj = s3_obj
        self._position = io.SEEK_SET

    def tell(self):
        return self._position

    def seek(self, offset, whence=io.SEEK_SET):
        if whence == io.SEEK_SET:
            self._position = offset
        elif whence == io.SEEK_CUR:
            self._position += offset
        else:
            self._position = self.obj.content_length-1 + offset

    def readable(self):
        return True

    def seekable(self):
        return True

    def read(self, size=-1):
        if size == 0:
            return b''
        if size is None or size < 0:
            rng = "bytes={}-".format(self._position)
        else:
            rng = "bytes={}-{}".format(self._position, self._position + size-1)
        resp = self.obj.get(Range=rng)
        self._position += resp['ContentLength']
        return resp['Body'].read()