takahe/users/models/identity.py

import base64
import uuid
from functools import partial
from typing import Optional, Tuple
from urllib.parse import urlparse

import httpx
import urlman
from asgiref.sync import async_to_sync, sync_to_async
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import rsa
from django.db import models
from django.utils import timezone
from OpenSSL import crypto

from core.ld import canonicalise
from stator.models import State, StateField, StateGraph, StatorModel
from users.models.domain import Domain


class IdentityStates(StateGraph):
    outdated = State(try_interval=3600)
    updated = State()

    outdated.transitions_to(updated)

    @classmethod
    async def handle_outdated(cls, identity: "Identity"):
        # Local identities never need fetching
        if identity.local:
            return "updated"
        # Run the actor fetch and progress to updated if it succeeds
        if await identity.fetch_actor():
            return "updated"


def upload_namer(prefix, instance, filename):
    """
    Names uploaded images etc.
    """
    now = timezone.now()
    filename = base64.b32encode(uuid.uuid4().bytes).decode("ascii")
    return f"{prefix}/{now.year}/{now.month}/{now.day}/{filename}"


class Identity(StatorModel):
    """
    Represents both local and remote Fediverse identities (actors)
    """

    # The Actor URI is essentially also a PK - we keep the default numeric
    # one around as well for making nice URLs etc.
    actor_uri = models.CharField(max_length=500, unique=True)

    state = StateField(IdentityStates)

    local = models.BooleanField()
    users = models.ManyToManyField(
        "users.User",
        related_name="identities",
        blank=True,
    )

    username = models.CharField(max_length=500, blank=True, null=True)
    # Must be a display domain if present
    domain = models.ForeignKey(
        "users.Domain",
        blank=True,
        null=True,
        on_delete=models.PROTECT,
    )

    name = models.CharField(max_length=500, blank=True, null=True)
    summary = models.TextField(blank=True, null=True)
    manually_approves_followers = models.BooleanField(blank=True, null=True)

    profile_uri = models.CharField(max_length=500, blank=True, null=True)
    inbox_uri = models.CharField(max_length=500, blank=True, null=True)
    outbox_uri = models.CharField(max_length=500, blank=True, null=True)
    icon_uri = models.CharField(max_length=500, blank=True, null=True)
    image_uri = models.CharField(max_length=500, blank=True, null=True)

    icon = models.ImageField(
        upload_to=partial(upload_namer, "profile_images"), blank=True, null=True
    )
    image = models.ImageField(
        upload_to=partial(upload_namer, "background_images"), blank=True, null=True
    )

    private_key = models.TextField(null=True, blank=True)
    public_key = models.TextField(null=True, blank=True)

    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)
    fetched = models.DateTimeField(null=True, blank=True)
    deleted = models.DateTimeField(null=True, blank=True)

    ### Model attributes ###

    class Meta:
        verbose_name_plural = "identities"
        unique_together = [("username", "domain")]

    class urls(urlman.Urls):
        view = "/@{self.username}@{self.domain_id}/"
        view_short = "/@{self.username}/"
        action = "{view}action/"
        activate = "{view}activate/"

        def get_scheme(self, url):
            return "https"

        def get_hostname(self, url):
            return self.instance.domain.uri_domain

    def __str__(self):
        if self.username and self.domain_id:
            return self.handle
        return self.actor_uri

    ### Alternate constructors/fetchers ###

    @classmethod
    def by_username_and_domain(cls, username, domain, fetch=False, local=False):
        if username.startswith("@"):
            raise ValueError("Username must not start with @")
        try:
            if local:
                return cls.objects.get(username=username, domain_id=domain, local=True)
            else:
                return cls.objects.get(username=username, domain_id=domain)
        except cls.DoesNotExist:
            if fetch and not local:
                actor_uri, handle = async_to_sync(cls.fetch_webfinger)(
                    f"{username}@{domain}"
                )
                username, domain = handle.split("@")
                domain = Domain.get_remote_domain(domain)
                return cls.objects.create(
                    actor_uri=actor_uri,
                    username=username,
                    domain_id=domain,
                    local=False,
                )
            return None

    @classmethod
    def by_actor_uri(cls, uri, create=False) -> "Identity":
        try:
            return cls.objects.get(actor_uri=uri)
        except cls.DoesNotExist:
            if create:
                return cls.objects.create(actor_uri=uri, local=False)
            else:
                raise KeyError(f"No identity found matching {uri}")

    ### Dynamic properties ###

    @property
    def name_or_handle(self):
        return self.name or self.handle

    @property
    def handle(self):
        if self.domain_id:
            return f"{self.username}@{self.domain_id}"
        return f"{self.username}@UNKNOWN-DOMAIN"

    @property
    def data_age(self) -> float:
        """
        How old our copy of this data is, in seconds
        """
        if self.local:
            return 0
        if self.fetched is None:
            return 10000000000
        return (timezone.now() - self.fetched).total_seconds()

    @property
    def outdated(self) -> bool:
        # TODO: Setting
        return self.data_age > 60 * 24 * 24

    @property
    def key_id(self):
        return self.actor_uri + "#main-key"

    ### Actor/Webfinger fetching ###

    @classmethod
    async def fetch_webfinger(cls, handle: str) -> Tuple[Optional[str], Optional[str]]:
        """
        Given a username@domain handle, returns a tuple of
        (actor uri, canonical handle) or None, None if it does not resolve.
        """
        domain = handle.split("@")[1]
        async with httpx.AsyncClient() as client:
            response = await client.get(
                f"https://{domain}/.well-known/webfinger?resource=acct:{handle}",
                headers={"Accept": "application/json"},
                follow_redirects=True,
            )
        if response.status_code >= 400:
            return None, None
        data = response.json()
        if data["subject"].startswith("acct:"):
            data["subject"] = data["subject"][5:]
        for link in data["links"]:
            if (
                link.get("type") == "application/activity+json"
                and link.get("rel") == "self"
            ):
                return link["href"], data["subject"]
        return None, None

    async def fetch_actor(self) -> bool:
        """
        Fetches the user's actor information, as well as their domain from
        webfinger if it's available.
        """
        if self.local:
            raise ValueError("Cannot fetch local identities")
        async with httpx.AsyncClient() as client:
            response = await client.get(
                self.actor_uri,
                headers={"Accept": "application/json"},
                follow_redirects=True,
            )
            if response.status_code >= 400:
                return False
            document = canonicalise(response.json(), include_security=True)
            self.name = document.get("name")
            self.profile_uri = document.get("url")
            self.inbox_uri = document.get("inbox")
            self.outbox_uri = document.get("outbox")
            self.summary = document.get("summary")
            self.username = document.get("preferredUsername")
            if self.username and "@value" in self.username:
                self.username = self.username["@value"]
            self.manually_approves_followers = document.get(
                "as:manuallyApprovesFollowers"
            )
            self.public_key = document.get("publicKey", {}).get("publicKeyPem")
            self.icon_uri = document.get("icon", {}).get("url")
            self.image_uri = document.get("image", {}).get("url")
        # Now go do webfinger with that info to see if we can get a canonical domain
        actor_url_parts = urlparse(self.actor_uri)
        get_domain = sync_to_async(Domain.get_remote_domain)
        if self.username:
            webfinger_actor, webfinger_handle = await self.fetch_webfinger(
                f"{self.username}@{actor_url_parts.hostname}"
            )
            if webfinger_handle:
                webfinger_username, webfinger_domain = webfinger_handle.split("@")
                self.username = webfinger_username
                self.domain = await get_domain(webfinger_domain)
            else:
                self.domain = await get_domain(actor_url_parts.hostname)
        else:
            self.domain = await get_domain(actor_url_parts.hostname)
        self.fetched = timezone.now()
        await sync_to_async(self.save)()
        return True

    ### Cryptography ###

    def generate_keypair(self):
        if not self.local:
            raise ValueError("Cannot generate keypair for remote user")
        private_key = rsa.generate_private_key(
            public_exponent=65537,
            key_size=2048,
        )
        self.private_key = private_key.private_bytes(
            encoding=serialization.Encoding.PEM,
            format=serialization.PrivateFormat.PKCS8,
            encryption_algorithm=serialization.NoEncryption(),
        ).decode("ascii")
        self.public_key = (
            private_key.public_key()
            .public_bytes(
                encoding=serialization.Encoding.PEM,
                format=serialization.PublicFormat.SubjectPublicKeyInfo,
            )
            .decode("ascii")
        )
        self.save()

    def sign(self, cleartext: str) -> bytes:
        if not self.private_key:
            raise ValueError("Cannot sign - no private key")
        pkey = crypto.load_privatekey(
            crypto.FILETYPE_PEM,
            self.private_key.encode("ascii"),
        )
        return crypto.sign(
            pkey,
            cleartext.encode("ascii"),
            "sha256",
        )

    def verify_signature(self, signature: bytes, cleartext: str) -> bool:
        if not self.public_key:
            raise ValueError("Cannot verify - no public key")
        x509 = crypto.X509()
        x509.set_pubkey(
            crypto.load_publickey(
                crypto.FILETYPE_PEM,
                self.public_key.encode("ascii"),
            )
        )
        try:
            crypto.verify(x509, signature, cleartext.encode("ascii"), "sha256")
        except crypto.Error:
            return False
        return True