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"""Reader objects to abstract out different body response types.

This module is package-private. It is not expected that these will
have any clients outside of httpplus.
"""
from __future__ import absolute_import

import httplib
import logging

logger = logging.getLogger(__name__)


class ReadNotReady(Exception):
    """Raised when read() is attempted but not enough data is loaded."""


class HTTPRemoteClosedError(httplib.HTTPException):
    """The server closed the remote socket in the middle of a response."""


class AbstractReader(object):
    """Abstract base class for response readers.

    Subclasses must implement _load, and should implement _close if
    it's not an error for the server to close their socket without
    some termination condition being detected during _load.
    """
    def __init__(self):
        self._finished = False
        self._done_chunks = []
        self.available_data = 0

    def _addchunk(self, data):
        self._done_chunks.append(data)
        self.available_data += len(data)

    def _pushchunk(self, data):
        self._done_chunks.insert(0, data)
        self.available_data += len(data)

    def _popchunk(self):
        b = self._done_chunks.pop(0)
        self.available_data -= len(b)

        return b

    def done(self):
        """Returns true if the response body is entirely read."""
        return self._finished

    def read(self, amt):
        """Read amt bytes from the response body."""
        if self.available_data < amt and not self._finished:
            raise ReadNotReady()
        blocks = []
        need = amt
        while self._done_chunks:
            b = self._popchunk()
            if len(b) > need:
                nb = b[:need]
                self._pushchunk(b[need:])
                b = nb
            blocks.append(b)
            need -= len(b)
            if need == 0:
                break
        result = ''.join(blocks)
        assert len(result) == amt or (self._finished and len(result) < amt)

        return result

    def readto(self, delimstr, blocks = None):
        """return available data chunks up to the first one in which
        delimstr occurs. No data will be returned after delimstr --
        the chunk in which it occurs will be split and the remainder
        pushed back onto the available data queue. If blocks is
        supplied chunks will be added to blocks, otherwise a new list
        will be allocated.
        """
        if blocks is None:
            blocks = []

        while self._done_chunks:
            b = self._popchunk()
            i = b.find(delimstr) + len(delimstr)
            if i:
                if i < len(b):
                    self._pushchunk(b[i:])
                blocks.append(b[:i])
                break
            else:
                blocks.append(b)

        return blocks

    def _load(self, data): # pragma: no cover
        """Subclasses must implement this.

        As data is available to be read out of this object, it should
        be placed into the _done_chunks list. Subclasses should not
        rely on data remaining in _done_chunks forever, as it may be
        reaped if the client is parsing data as it comes in.
        """
        raise NotImplementedError

    def _close(self):
        """Default implementation of close.

        The default implementation assumes that the reader will mark
        the response as finished on the _finished attribute once the
        entire response body has been read. In the event that this is
        not true, the subclass should override the implementation of
        close (for example, close-is-end responses have to set
        self._finished in the close handler.)
        """
        if not self._finished:
            raise HTTPRemoteClosedError(
                'server appears to have closed the socket mid-response')


class AbstractSimpleReader(AbstractReader):
    """Abstract base class for simple readers that require no response decoding.

    Examples of such responses are Connection: Close (close-is-end)
    and responses that specify a content length.
    """
    def _load(self, data):
        if data:
            assert not self._finished, (
                'tried to add data (%r) to a closed reader!' % data)
        logger.debug('%s read an additional %d data',
                     self.name, len(data)) # pylint: disable=E1101
        self._addchunk(data)


class CloseIsEndReader(AbstractSimpleReader):
    """Reader for responses that specify Connection: Close for length."""
    name = 'close-is-end'

    def _close(self):
        logger.info('Marking close-is-end reader as closed.')
        self._finished = True


class ContentLengthReader(AbstractSimpleReader):
    """Reader for responses that specify an exact content length."""
    name = 'content-length'

    def __init__(self, amount):
        AbstractSimpleReader.__init__(self)
        self._amount = amount
        if amount == 0:
            self._finished = True
        self._amount_seen = 0

    def _load(self, data):
        AbstractSimpleReader._load(self, data)
        self._amount_seen += len(data)
        if self._amount_seen >= self._amount:
            self._finished = True
            logger.debug('content-length read complete')


class ChunkedReader(AbstractReader):
    """Reader for chunked transfer encoding responses."""
    def __init__(self, eol):
        AbstractReader.__init__(self)
        self._eol = eol
        self._leftover_skip_amt = 0
        self._leftover_data = ''

    def _load(self, data):
        assert not self._finished, 'tried to add data to a closed reader!'
        logger.debug('chunked read an additional %d data', len(data))
        position = 0
        if self._leftover_data:
            logger.debug(
                'chunked reader trying to finish block from leftover data')
            # TODO: avoid this string concatenation if possible
            data = self._leftover_data + data
            position = self._leftover_skip_amt
            self._leftover_data = ''
            self._leftover_skip_amt = 0
        datalen = len(data)
        while position < datalen:
            split = data.find(self._eol, position)
            if split == -1:
                self._leftover_data = data
                self._leftover_skip_amt = position
                return
            amt = int(data[position:split], base=16)
            block_start = split + len(self._eol)
            # If the whole data chunk plus the eol trailer hasn't
            # loaded, we'll wait for the next load.
            if block_start + amt + len(self._eol) > len(data):
                self._leftover_data = data
                self._leftover_skip_amt = position
                return
            if amt == 0:
                self._finished = True
                logger.debug('closing chunked reader due to chunk of length 0')
                return
            self._addchunk(data[block_start:block_start + amt])
            position = block_start + amt + len(self._eol)
# no-check-code
