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path: root/backends/leap_backend.py
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"""
A U1DB backend that encrypts data before sending to server and decrypts after
receiving.
"""

try:
    import simplejson as json
except ImportError:
    import json  # noqa

from u1db import Document
from u1db.remote import utils
from u1db.remote.http_target import HTTPSyncTarget
from u1db.remote.http_database import HTTPDatabase
from u1db.errors import BrokenSyncStream

import uuid


class NoDefaultKey(Exception):
    """
    Exception to signal that there's no default OpenPGP key configured.
    """
    pass


class NoSoledadInstance(Exception):
    """
    Exception to signal that no Soledad instance was found.
    """
    pass


class DocumentNotEncrypted(Exception):
    """
    Exception to signal failures in document encryption.
    """
    pass


class LeapDocument(Document):
    """
    Encryptable and syncable document.

    LEAP Documents are standard u1db documents with cabability of returning an
    encrypted version of the document json string as well as setting document
    content based on an encrypted version of json string.
    """

    def __init__(self, doc_id=None, rev=None, json='{}', has_conflicts=False,
                 encrypted_json=None, soledad=None, syncable=True):
        super(LeapDocument, self).__init__(doc_id, rev, json, has_conflicts)
        self._soledad = soledad
        self._syncable = syncable
        if encrypted_json:
            self.set_encrypted_json(encrypted_json)

    def get_encrypted_content(self):
        """
        Return an encrypted JSON serialization of document's contents.
        """
        if not self._soledad:
            raise NoSoledadInstance()
        return self._soledad.encrypt_symmetric(self.doc_id,
                                               self.get_json())

    def set_encrypted_content(self, cyphertext):
        """
        Set document's content based on an encrypted JSON serialization of
        contents.
        """
        plaintext = self._soledad.decrypt_symmetric(self.doc_id, cyphertext)
        return self.set_json(plaintext)

    def get_encrypted_json(self):
        """
        Return a valid JSON string containing document's content encrypted to
        the user's public key.
        """
        return json.dumps({'_encrypted_json': self.get_encrypted_content()})

    def set_encrypted_json(self, encrypted_json):
        """
        Set document's content based on a valid JSON string containing the
        encrypted document's contents.
        """
        if not self._soledad:
            raise NoSoledadInstance()
        cyphertext = json.loads(encrypted_json)['_encrypted_json']
        self.set_encrypted_content(cyphertext)

    def _get_syncable(self):
        return self._syncable

    def _set_syncable(self, syncable=True):
        self._syncable = syncable

    syncable = property(
        _get_syncable,
        _set_syncable,
        doc="Determine if document should be synced with server."
    )

    # Returning the revision as string solves the following exception in
    # Twisted web:
    #     exceptions.TypeError: Can only pass-through bytes on Python 2
    def _get_rev(self):
        if self._rev is None:
            return None
        return str(self._rev)

    def _set_rev(self, rev):
        self._rev = rev

    rev = property(
        _get_rev,
        _set_rev,
        doc="Wrapper to ensure `doc.rev` is always returned as bytes.")


class LeapSyncTarget(HTTPSyncTarget):
    """
    A SyncTarget that encrypts data before sending and decrypts data after
    receiving.
    """

    def __init__(self, url, creds=None, soledad=None):
        super(LeapSyncTarget, self).__init__(url, creds)
        self._soledad = soledad

    def _parse_sync_stream(self, data, return_doc_cb, ensure_callback=None):
        """
        Does the same as parent's method but ensures incoming content will be
        decrypted.
        """
        parts = data.splitlines()  # one at a time
        if not parts or parts[0] != '[':
            raise BrokenSyncStream
        data = parts[1:-1]
        comma = False
        if data:
            line, comma = utils.check_and_strip_comma(data[0])
            res = json.loads(line)
            if ensure_callback and 'replica_uid' in res:
                ensure_callback(res['replica_uid'])
            for entry in data[1:]:
                if not comma:  # missing in between comma
                    raise BrokenSyncStream
                line, comma = utils.check_and_strip_comma(entry)
                entry = json.loads(line)
                # decrypt after receiving from server.
                if not self._soledad:
                    raise NoSoledadInstance()
                enc_json = json.loads(entry['content'])['_encrypted_json']
                if not self._soledad.is_encrypted_sym(enc_json):
                    raise DocumentNotEncrypted(
                        "Incoming document from sync is not encrypted.")
                doc = LeapDocument(entry['id'], entry['rev'],
                                   encrypted_json=entry['content'],
                                   soledad=self._soledad)
                return_doc_cb(doc, entry['gen'], entry['trans_id'])
        if parts[-1] != ']':
            try:
                partdic = json.loads(parts[-1])
            except ValueError:
                pass
            else:
                if isinstance(partdic, dict):
                    self._error(partdic)
            raise BrokenSyncStream
        if not data or comma:  # no entries or bad extra comma
            raise BrokenSyncStream
        return res

    def sync_exchange(self, docs_by_generations, source_replica_uid,
                      last_known_generation, last_known_trans_id,
                      return_doc_cb, ensure_callback=None):
        """
        Does the same as parent's method but encrypts content before syncing.
        """
        self._ensure_connection()
        if self._trace_hook:  # for tests
            self._trace_hook('sync_exchange')
        url = '%s/sync-from/%s' % (self._url.path, source_replica_uid)
        self._conn.putrequest('POST', url)
        self._conn.putheader('content-type', 'application/x-u1db-sync-stream')
        for header_name, header_value in self._sign_request('POST', url, {}):
            self._conn.putheader(header_name, header_value)
        entries = ['[']
        size = 1

        def prepare(**dic):
            entry = comma + '\r\n' + json.dumps(dic)
            entries.append(entry)
            return len(entry)

        comma = ''
        size += prepare(
            last_known_generation=last_known_generation,
            last_known_trans_id=last_known_trans_id,
            ensure=ensure_callback is not None)
        comma = ','
        for doc, gen, trans_id in docs_by_generations:
            if doc.syncable:
                # encrypt and verify before sending to server.
                enc_json = json.loads(
                    doc.get_encrypted_json())['_encrypted_json']
                if not self._soledad.is_encrypted_sym(enc_json):
                    raise DocumentNotEncrypted(
                        "Could not encrypt document before sync.")
                size += prepare(id=doc.doc_id, rev=doc.rev,
                                content=doc.get_encrypted_json(),
                                gen=gen, trans_id=trans_id)
        entries.append('\r\n]')
        size += len(entries[-1])
        self._conn.putheader('content-length', str(size))
        self._conn.endheaders()
        for entry in entries:
            self._conn.send(entry)
        entries = None
        data, _ = self._response()
        res = self._parse_sync_stream(data, return_doc_cb, ensure_callback)
        data = None
        return res['new_generation'], res['new_transaction_id']