upstream-zulip/zerver/lib/email_mirror_helpers.py

import re
from collections.abc import Callable
from typing import Any

from django.conf import settings
from django.utils.text import slugify

from zerver.models import ChannelEmailAddress, Stream, UserProfile


def default_option_handler_factory(address_option: str) -> Callable[[dict[str, Any]], None]:
    def option_setter(options_dict: dict[str, Any]) -> None:
        options_dict[address_option.replace("-", "_")] = True

    return option_setter


optional_address_tokens = {
    "show-sender": default_option_handler_factory("show-sender"),
    "include-footer": default_option_handler_factory("include-footer"),
    "include-quotes": default_option_handler_factory("include-quotes"),
    "prefer-text": lambda options: options.update(prefer_text=True),
    "prefer-html": lambda options: options.update(prefer_text=False),
}


class ZulipEmailForwardError(Exception):
    pass


class ZulipEmailForwardUserError(ZulipEmailForwardError):
    pass


def get_email_gateway_message_string_from_address(address: str) -> str:
    if settings.EMAIL_GATEWAY_PATTERN == "":
        raise ZulipEmailForwardError("This server is not configured for incoming email.")
    pattern_parts = [re.escape(part) for part in settings.EMAIL_GATEWAY_PATTERN.split("%s")]
    if settings.EMAIL_GATEWAY_EXTRA_PATTERN_HACK:
        # Accept mails delivered to any Zulip server
        pattern_parts[-1] = settings.EMAIL_GATEWAY_EXTRA_PATTERN_HACK
    match_email_re = re.compile(r"(.*?)".join(pattern_parts))
    match = match_email_re.match(address)

    if not match:
        raise ZulipEmailForwardError("Address not recognized by gateway.")
    msg_string = match.group(1)

    return msg_string


def get_channel_email_token(stream: Stream, *, creator: UserProfile, sender: UserProfile) -> str:
    channel_email_address, _created = ChannelEmailAddress.objects.get_or_create(
        realm=stream.realm,
        channel=stream,
        creator=creator,
        sender=sender,
    )
    return channel_email_address.email_token


def encode_email_address(name: str, email_token: str, show_sender: bool = False) -> str:
    # Some deployments may not use the email gateway
    if settings.EMAIL_GATEWAY_PATTERN == "":
        return ""

    # Given the fact that we have almost no restrictions on stream names and
    # that what characters are allowed in e-mail addresses is complicated and
    # dependent on context in the address, we opt for a simple scheme:
    # 1. Replace all substrings of non-alphanumeric characters with a single hyphen.
    # 2. Use Django's slugify to convert the resulting name to ascii.
    # 3. If the resulting name is shorter than the name we got in step 1,
    # it means some letters can't be reasonably turned to ascii and have to be dropped,
    # which would mangle the name, so we just skip the name part of the address.
    name = re.sub(r"\W+", "-", name)
    slug_name = slugify(name)
    encoded_name = slug_name if len(slug_name) == len(name) else ""

    # If encoded_name ends up empty, we just skip this part of the address:
    if encoded_name:
        encoded_token = f"{encoded_name}.{email_token}"
    else:
        encoded_token = email_token

    if show_sender:
        encoded_token += ".show-sender"

    return settings.EMAIL_GATEWAY_PATTERN % (encoded_token,)


def decode_email_address(email: str) -> tuple[str, dict[str, bool]]:
    # Perform the reverse of encode_email_address. Returns a tuple of
    # (email_token, options)
    msg_string = get_email_gateway_message_string_from_address(email)

    # Support both + and . as separators.  For background, the `+` is
    # more aesthetically pleasing, but because Google groups silently
    # drops the use of `+` in email addresses, which would completely
    # break the integration, we now favor `.` as the separator between
    # tokens in the email addresses we generate.
    #
    # We need to keep supporting `+` indefinitely for backwards
    # compatibility with older versions of Zulip that offered users
    # email addresses prioritizing using `+` for better aesthetics.
    msg_string = msg_string.replace(".", "+")

    parts = msg_string.split("+")
    options: dict[str, bool] = {}
    for part in parts:
        if part in optional_address_tokens:
            optional_address_tokens[part](options)

    remaining_parts = [part for part in parts if part not in optional_address_tokens]

    # There should be one or two parts left:
    # [stream_name, email_token] or just [email_token]
    if len(remaining_parts) == 1:
        token = remaining_parts[0]
    else:
        token = remaining_parts[1]

    return token, options