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Filename : decoder.py
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# -*- coding: utf-8 -*-
"""

requests_toolbelt.multipart.decoder
===================================

This holds all the implementation details of the MultipartDecoder

"""

import sys
import email.parser
from .encoder import encode_with
from requests.structures import CaseInsensitiveDict


def _split_on_find(content, bound):
    point = content.find(bound)
    return content[:point], content[point + len(bound):]


class ImproperBodyPartContentException(Exception):
    pass


class NonMultipartContentTypeException(Exception):
    pass


def _header_parser(string, encoding):
    major = sys.version_info[0]
    if major == 3:
        string = string.decode(encoding)
    headers = email.parser.HeaderParser().parsestr(string).items()
    return (
        (encode_with(k, encoding), encode_with(v, encoding))
        for k, v in headers
    )


class BodyPart(object):
    """

    The ``BodyPart`` object is a ``Response``-like interface to an individual
    subpart of a multipart response. It is expected that these will
    generally be created by objects of the ``MultipartDecoder`` class.

    Like ``Response``, there is a ``CaseInsensitiveDict`` object named header,
    ``content`` to access bytes, ``text`` to access unicode, and ``encoding``
    to access the unicode codec.

    """

    def __init__(self, content, encoding):
        self.encoding = encoding
        headers = {}
        # Split into header section (if any) and the content
        if b'\r\n\r\n' in content:
            first, self.content = _split_on_find(content, b'\r\n\r\n')
            if first != b'':
                headers = _header_parser(first.lstrip(), encoding)
        else:
            raise ImproperBodyPartContentException(
                'content does not contain CR-LF-CR-LF'
            )
        self.headers = CaseInsensitiveDict(headers)

    @property
    def text(self):
        """Content of the ``BodyPart`` in unicode."""
        return self.content.decode(self.encoding)


class MultipartDecoder(object):
    """

    The ``MultipartDecoder`` object parses the multipart payload of
    a bytestring into a tuple of ``Response``-like ``BodyPart`` objects.

    The basic usage is::

        import requests
        from requests_toolbelt import MultipartDecoder

        response = request.get(url)
        decoder = MultipartDecoder.from_response(response)
        for part in decoder.parts:
            print(part.header['content-type'])

    If the multipart content is not from a response, basic usage is::

        from requests_toolbelt import MultipartDecoder

        decoder = MultipartDecoder(content, content_type)
        for part in decoder.parts:
            print(part.header['content-type'])

    For both these usages, there is an optional ``encoding`` parameter. This is
    a string, which is the name of the unicode codec to use (default is
    ``'utf-8'``).

    """
    def __init__(self, content, content_type, encoding='utf-8'):
        #: Original content
        self.content = content
        #: Original Content-Type header
        self.content_type = content_type
        #: Response body encoding
        self.encoding = encoding
        #: Parsed parts of the multipart response body
        self.parts = tuple()
        self._find_boundary()
        self._parse_body()

    def _find_boundary(self):
        ct_info = tuple(x.strip() for x in self.content_type.split(';'))
        mimetype = ct_info[0]
        if mimetype.split('/')[0] != 'multipart':
            raise NonMultipartContentTypeException(
                "Unexpected mimetype in content-type: '{0}'".format(mimetype)
            )
        for item in ct_info[1:]:
            attr, value = _split_on_find(
                item,
                '='
            )
            if attr.lower() == 'boundary':
                self.boundary = encode_with(value.strip('"'), self.encoding)

    @staticmethod
    def _fix_first_part(part, boundary_marker):
        bm_len = len(boundary_marker)
        if boundary_marker == part[:bm_len]:
            return part[bm_len:]
        else:
            return part

    def _parse_body(self):
        boundary = b''.join((b'--', self.boundary))

        def body_part(part):
            fixed = MultipartDecoder._fix_first_part(part, boundary)
            return BodyPart(fixed, self.encoding)

        def test_part(part):
            return (part != b'' and
                    part != b'\r\n' and
                    part[:4] != b'--\r\n' and
                    part != b'--')

        parts = self.content.split(b''.join((b'\r\n', boundary)))
        self.parts = tuple(body_part(x) for x in parts if test_part(x))

    @classmethod
    def from_response(cls, response, encoding='utf-8'):
        content = response.content
        content_type = response.headers.get('content-type', None)
        return cls(content, content_type, encoding)