pyssb/ssb/feed/models.py

# SPDX-License-Identifier: MIT
#
# Copyright (c) 2017 PySSB contributors (see AUTHORS for more details)
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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# SOFTWARE.

"""Feed models"""

from base64 import b64encode
from collections import OrderedDict, namedtuple
from datetime import datetime
from hashlib import sha256

from simplejson import dumps, loads

from ssb.util import tag

OrderedMsg = namedtuple("OrderedMsg", ("previous", "author", "sequence", "timestamp", "hash", "content"))


class NoPrivateKeyException(Exception):
    """Exception to raise when a private key is not available"""


def to_ordered(data):
    """Convert a dictionary to an ``OrderedDict``"""

    smsg = OrderedMsg(**data)

    return OrderedDict((k, getattr(smsg, k)) for k in smsg._fields)


def get_millis_1970():
    """Get the UNIX timestamp in milliseconds"""

    return int(datetime.utcnow().timestamp() * 1000)


class Feed:
    """Base class for feeds"""

    def __init__(self, public_key):
        self.public_key = public_key

    @property
    def id(self):
        """The identifier of the feed"""

        return tag(self.public_key).decode("ascii")

    def sign(self, msg):
        """Sign a message"""

        raise NoPrivateKeyException("Cannot use remote identity to sign (no private key!)")


class LocalFeed(Feed):
    """Class representing a local feed"""

    def __init__(self, private_key):  # pylint: disable=super-init-not-called
        self.private_key = private_key

    @property
    def public_key(self):
        """The public key of the feed"""

        return self.private_key.verify_key

    def sign(self, msg):
        """Sign a message for this feed"""

        return self.private_key.sign(msg).signature


class Message:
    """Base class for SSB messages"""

    def __init__(  # pylint: disable=too-many-arguments
        self, feed, content, signature=None, sequence=1, timestamp=None, previous=None
    ):
        self.feed = feed
        self.content = content

        if signature is None:
            raise ValueError("signature can't be None")
        self.signature = signature

        self.previous = previous
        if self.previous:
            self.sequence = self.previous.sequence + 1
        else:
            self.sequence = sequence

        self.timestamp = get_millis_1970() if timestamp is None else timestamp

    @classmethod
    def parse(cls, data, feed):
        """Parse raw message data"""

        obj = loads(data, object_pairs_hook=OrderedDict)
        msg = cls(feed, obj["content"], timestamp=obj["timestamp"])

        return msg

    def serialize(self, add_signature=True):
        """Serialize the message"""

        return dumps(self.to_dict(add_signature=add_signature), indent=2).encode("utf-8")

    def to_dict(self, add_signature=True):
        """Convert the message to a dictionary"""

        obj = to_ordered(
            {
                "previous": self.previous.key if self.previous else None,
                "author": self.feed.id,
                "sequence": self.sequence,
                "timestamp": self.timestamp,
                "hash": "sha256",
                "content": self.content,
            }
        )

        if add_signature:
            obj["signature"] = self.signature

        return obj

    def verify(self, signature):
        """Verify the signature of the message"""

        return self.signature == signature

    @property
    def hash(self):
        """The cryptographic hash of the message"""

        hash_ = sha256(self.serialize()).digest()
        return b64encode(hash_).decode("ascii") + ".sha256"

    @property
    def key(self):
        """The key of the message"""

        return "%" + self.hash


class LocalMessage(Message):
    """Class representing a local message"""

    def __init__(  # pylint: disable=too-many-arguments,super-init-not-called
        self, feed, content, signature=None, sequence=1, timestamp=None, previous=None
    ):
        self.feed = feed
        self.content = content

        self.previous = previous
        if self.previous:
            self.sequence = self.previous.sequence + 1
        else:
            self.sequence = sequence

        self.timestamp = get_millis_1970() if timestamp is None else timestamp

        if signature is None:
            self.signature = self._sign()
        else:
            self.signature = signature

    def _sign(self):
        # ensure ordering of keys and indentation of 2 characters, like ssb-keys
        data = self.serialize(add_signature=False)
        return (b64encode(bytes(self.feed.sign(data))) + b".sig.ed25519").decode("ascii")