django-anymail/anymail/webhooks/mailgun.py

import json
from datetime import datetime

import hashlib
import hmac
from django.utils.crypto import constant_time_compare
from django.utils.timezone import utc

from .base import AnymailBaseWebhookView
from ..exceptions import AnymailConfigurationError, AnymailWebhookValidationFailure, AnymailInvalidAddress
from ..inbound import AnymailInboundMessage
from ..signals import inbound, tracking, AnymailInboundEvent, AnymailTrackingEvent, EventType, RejectReason
from ..utils import get_anymail_setting, combine, querydict_getfirst, parse_single_address, UNSET


class MailgunBaseWebhookView(AnymailBaseWebhookView):
    """Base view class for Mailgun webhooks"""

    esp_name = "Mailgun"
    warn_if_no_basic_auth = False  # because we validate against signature

    webhook_signing_key = None  # (Declaring class attr allows override by kwargs in View.as_view.)

    # The `api_key` attribute name is still allowed for compatibility with earlier Anymail releases.
    api_key = None  # (Declaring class attr allows override by kwargs in View.as_view.)

    def __init__(self, **kwargs):
        # webhook_signing_key: falls back to api_key if webhook_signing_key not provided
        api_key = get_anymail_setting('api_key', esp_name=self.esp_name,
                                      kwargs=kwargs, allow_bare=True, default=None)
        webhook_signing_key = get_anymail_setting('webhook_signing_key', esp_name=self.esp_name,
                                                  kwargs=kwargs, default=UNSET if api_key is None else api_key)
        self.webhook_signing_key = webhook_signing_key.encode('ascii')  # hmac.new requires bytes key
        super().__init__(**kwargs)

    def validate_request(self, request):
        super().validate_request(request)  # first check basic auth if enabled
        if request.content_type == "application/json":
            # New-style webhook: json payload with separate signature block
            try:
                event = json.loads(request.body.decode('utf-8'))
                signature_block = event['signature']
                token = signature_block['token']
                timestamp = signature_block['timestamp']
                signature = signature_block['signature']
            except (KeyError, ValueError, UnicodeDecodeError) as err:
                raise AnymailWebhookValidationFailure(
                    "Mailgun webhook called with invalid payload format") from err
        else:
            # Legacy webhook: signature fields are interspersed with other POST data
            try:
                # Must use the *last* value of these fields if there are conflicting merged user-variables.
                # (Fortunately, Django QueryDict is specced to return the last value.)
                token = request.POST['token']
                timestamp = request.POST['timestamp']
                signature = request.POST['signature']
            except KeyError as err:
                raise AnymailWebhookValidationFailure(
                    "Mailgun webhook called without required security fields") from err

        expected_signature = hmac.new(key=self.webhook_signing_key, msg='{}{}'.format(timestamp, token).encode('ascii'),
                                      digestmod=hashlib.sha256).hexdigest()
        if not constant_time_compare(signature, expected_signature):
            raise AnymailWebhookValidationFailure("Mailgun webhook called with incorrect signature")


class MailgunTrackingWebhookView(MailgunBaseWebhookView):
    """Handler for Mailgun delivery and engagement tracking webhooks"""

    signal = tracking

    def parse_events(self, request):
        if request.content_type == "application/json":
            esp_event = json.loads(request.body.decode('utf-8'))
            return [self.esp_to_anymail_event(esp_event)]
        else:
            return [self.mailgun_legacy_to_anymail_event(request.POST)]

    event_types = {
        # Map Mailgun event: Anymail normalized type
        'accepted': EventType.QUEUED,  # not delivered to webhooks (8/2018)
        'rejected': EventType.REJECTED,
        'delivered': EventType.DELIVERED,
        'failed': EventType.BOUNCED,
        'opened': EventType.OPENED,
        'clicked': EventType.CLICKED,
        'unsubscribed': EventType.UNSUBSCRIBED,
        'complained': EventType.COMPLAINED,
    }

    reject_reasons = {
        # Map Mailgun event_data.reason: Anymail normalized RejectReason
        # (these appear in webhook doc examples, but aren't actually documented anywhere)
        "bounce": RejectReason.BOUNCED,
        "suppress-bounce": RejectReason.BOUNCED,
        "generic": RejectReason.OTHER,  # ??? appears to be used for any temporary failure?
    }

    severities = {
        # Remap some event types based on "severity" payload field
        (EventType.BOUNCED, 'temporary'): EventType.DEFERRED
    }

    def esp_to_anymail_event(self, esp_event):
        event_data = esp_event.get('event-data', {})

        event_type = self.event_types.get(event_data['event'], EventType.UNKNOWN)

        event_type = self.severities.get((EventType.BOUNCED, event_data.get('severity')), event_type)

        # Use signature.token for event_id, rather than event_data.id,
        # because the latter is only "guaranteed to be unique within a day".
        event_id = esp_event.get('signature', {}).get('token')

        recipient = event_data.get('recipient')

        try:
            timestamp = datetime.fromtimestamp(float(event_data['timestamp']), tz=utc)
        except KeyError:
            timestamp = None

        try:
            message_id = event_data['message']['headers']['message-id']
        except KeyError:
            message_id = None
        if message_id and not message_id.startswith('<'):
            message_id = "<{}>".format(message_id)

        metadata = event_data.get('user-variables', {})
        tags = event_data.get('tags', [])

        try:
            delivery_status = event_data['delivery-status']
        except KeyError:
            description = None
            mta_response = None
        else:
            description = delivery_status.get('description')
            mta_response = delivery_status.get('message')

        if 'reason' in event_data:
            reject_reason = self.reject_reasons.get(event_data['reason'], RejectReason.OTHER)
        else:
            reject_reason = None

        if event_type == EventType.REJECTED:
            # This event has a somewhat different structure than the others...
            description = description or event_data.get("reject", {}).get("reason")
            reject_reason = reject_reason or RejectReason.OTHER
            if not recipient:
                try:
                    to_email = parse_single_address(
                        event_data["message"]["headers"]["to"])
                except (AnymailInvalidAddress, KeyError):
                    pass
                else:
                    recipient = to_email.addr_spec

        return AnymailTrackingEvent(
            event_type=event_type,
            timestamp=timestamp,
            message_id=message_id,
            event_id=event_id,
            recipient=recipient,
            reject_reason=reject_reason,
            description=description,
            mta_response=mta_response,
            tags=tags,
            metadata=metadata,
            click_url=event_data.get('url'),
            user_agent=event_data.get('client-info', {}).get('user-agent'),
            esp_event=esp_event,
        )

    # Legacy event handling
    # (Prior to 2018-06-29, these were the only Mailgun events.)

    legacy_event_types = {
        # Map Mailgun event: Anymail normalized type
        'delivered': EventType.DELIVERED,
        'dropped': EventType.REJECTED,
        'bounced': EventType.BOUNCED,
        'complained': EventType.COMPLAINED,
        'unsubscribed': EventType.UNSUBSCRIBED,
        'opened': EventType.OPENED,
        'clicked': EventType.CLICKED,
        # Mailgun does not send events corresponding to QUEUED or DEFERRED
    }

    legacy_reject_reasons = {
        # Map Mailgun (SMTP) error codes to Anymail normalized reject_reason.
        # By default, we will treat anything 400-599 as REJECT_BOUNCED
        # so only exceptions are listed here.
        499: RejectReason.TIMED_OUT,  # unable to connect to MX (also covers invalid recipients)
        # These 6xx codes appear to be Mailgun extensions to SMTP
        # (and don't seem to be documented anywhere):
        605: RejectReason.BOUNCED,  # previous bounce
        607: RejectReason.SPAM,  # previous spam complaint
    }

    def mailgun_legacy_to_anymail_event(self, esp_event):
        # esp_event is a Django QueryDict (from request.POST),
        # which has multi-valued fields, but is *not* case-insensitive.
        # Because of the way Mailgun merges user-variables into the event,
        # we must generally use the *first* value of any multi-valued field
        # to avoid potential conflicting user-data.
        esp_event.getfirst = querydict_getfirst.__get__(esp_event)

        if 'event' not in esp_event and 'sender' in esp_event:
            # Inbound events don't (currently) have an event field
            raise AnymailConfigurationError(
                "You seem to have set Mailgun's *inbound* route "
                "to Anymail's Mailgun *tracking* webhook URL.")

        event_type = self.legacy_event_types.get(esp_event.getfirst('event'), EventType.UNKNOWN)
        timestamp = datetime.fromtimestamp(int(esp_event['timestamp']), tz=utc)  # use *last* value of timestamp
        # Message-Id is not documented for every event, but seems to always be included.
        # (It's sometimes spelled as 'message-id', lowercase, and missing the <angle-brackets>.)
        message_id = esp_event.getfirst('Message-Id', None) or esp_event.getfirst('message-id', None)
        if message_id and not message_id.startswith('<'):
            message_id = "<{}>".format(message_id)

        description = esp_event.getfirst('description', None)
        mta_response = esp_event.getfirst('error', None) or esp_event.getfirst('notification', None)
        reject_reason = None
        try:
            mta_status = int(esp_event.getfirst('code'))
        except (KeyError, TypeError):
            pass
        except ValueError:
            # RFC-3463 extended SMTP status code (class.subject.detail, where class is "2", "4" or "5")
            try:
                status_class = esp_event.getfirst('code').split('.')[0]
            except (TypeError, IndexError):
                # illegal SMTP status code format
                pass
            else:
                reject_reason = RejectReason.BOUNCED if status_class in ("4", "5") else RejectReason.OTHER
        else:
            reject_reason = self.legacy_reject_reasons.get(
                mta_status,
                RejectReason.BOUNCED if 400 <= mta_status < 600
                else RejectReason.OTHER)

        metadata = self._extract_legacy_metadata(esp_event)

        # tags are supposed to be in 'tag' fields, but are sometimes in undocumented X-Mailgun-Tag
        tags = esp_event.getlist('tag', None) or esp_event.getlist('X-Mailgun-Tag', [])

        return AnymailTrackingEvent(
            event_type=event_type,
            timestamp=timestamp,
            message_id=message_id,
            event_id=esp_event.get('token', None),  # use *last* value of token
            recipient=esp_event.getfirst('recipient', None),
            reject_reason=reject_reason,
            description=description,
            mta_response=mta_response,
            tags=tags,
            metadata=metadata,
            click_url=esp_event.getfirst('url', None),
            user_agent=esp_event.getfirst('user-agent', None),
            esp_event=esp_event,
        )

    def _extract_legacy_metadata(self, esp_event):
        # Mailgun merges user-variables into the POST fields. If you know which user variable
        # you want to retrieve--and it doesn't conflict with a Mailgun event field--that's fine.
        # But if you want to extract all user-variables (like we do), it's more complicated...
        event_type = esp_event.getfirst('event')
        metadata = {}

        if 'message-headers' in esp_event:
            # For events where original message headers are available, it's most reliable
            # to recover user-variables from the X-Mailgun-Variables header(s).
            headers = json.loads(esp_event['message-headers'])
            variables = [value for [field, value] in headers if field == 'X-Mailgun-Variables']
            if len(variables) >= 1:
                # Each X-Mailgun-Variables value is JSON. Parse and merge them all into single dict:
                metadata = combine(*[json.loads(value) for value in variables])

        elif event_type in self._known_legacy_event_fields:
            # For other events, we must extract from the POST fields, ignoring known Mailgun
            # event parameters, and treating all other values as user-variables.
            known_fields = self._known_legacy_event_fields[event_type]
            for field, values in esp_event.lists():
                if field not in known_fields:
                    # Unknown fields are assumed to be user-variables. (There should really only be
                    # a single value, but just in case take the last one to match QueryDict semantics.)
                    metadata[field] = values[-1]
                elif field == 'tag':
                    # There's no way to distinguish a user-variable named 'tag' from an actual tag,
                    # so don't treat this/these value(s) as metadata.
                    pass
                elif len(values) == 1:
                    # This is an expected event parameter, and since there's only a single value
                    # it must be the event param, not metadata.
                    pass
                else:
                    # This is an expected event parameter, but there are (at least) two values.
                    # One is the event param, and the other is a user-variable metadata value.
                    # Which is which depends on the field:
                    if field in {'signature', 'timestamp', 'token'}:
                        metadata[field] = values[0]  # values = [user-variable, event-param]
                    else:
                        metadata[field] = values[-1]  # values = [event-param, user-variable]

        return metadata

    _common_legacy_event_fields = {
        # These fields are documented to appear in all Mailgun opened, clicked and unsubscribed events:
        'event', 'recipient', 'domain', 'ip', 'country', 'region', 'city', 'user-agent', 'device-type',
        'client-type', 'client-name', 'client-os', 'campaign-id', 'campaign-name', 'tag', 'mailing-list',
        'timestamp', 'token', 'signature',
        # Undocumented, but observed in actual events:
        'body-plain', 'h', 'message-id',
    }
    _known_legacy_event_fields = {
        # For all Mailgun event types that *don't* include message-headers,
        # map Mailgun (not normalized) event type to set of expected event fields.
        # Used for metadata extraction.
        'clicked': _common_legacy_event_fields | {'url'},
        'opened': _common_legacy_event_fields,
        'unsubscribed': _common_legacy_event_fields,
    }


class MailgunInboundWebhookView(MailgunBaseWebhookView):
    """Handler for Mailgun inbound (route forward-to-url) webhook"""

    signal = inbound

    def parse_events(self, request):
        if request.content_type == "application/json":
            esp_event = json.loads(request.body.decode('utf-8'))
            event_type = esp_event.get('event-data', {}).get('event', '')
            raise AnymailConfigurationError(
                "You seem to have set Mailgun's *%s tracking* webhook "
                "to Anymail's Mailgun *inbound* webhook URL. "
                "(Or Mailgun has changed inbound events to use json.)"
                % event_type)
        return [self.esp_to_anymail_event(request)]

    def esp_to_anymail_event(self, request):
        # Inbound uses the entire Django request as esp_event, because we need POST and FILES.
        # Note that request.POST is case-sensitive (unlike email.message.Message headers).
        esp_event = request

        if request.POST.get('event', 'inbound') != 'inbound':
            # (Legacy) tracking event
            raise AnymailConfigurationError(
                "You seem to have set Mailgun's *%s tracking* webhook "
                "to Anymail's Mailgun *inbound* webhook URL." % request.POST['event'])

        if 'attachments' in request.POST:
            # Inbound route used store() rather than forward().
            # ("attachments" seems to be the only POST param that differs between
            # store and forward; Anymail could support store by handling the JSON
            # attachments param in message_from_mailgun_parsed.)
            raise AnymailConfigurationError(
                "You seem to have configured Mailgun's receiving route using the store()"
                " action. Anymail's inbound webhook requires the forward() action.")

        if 'body-mime' in request.POST:
            # Raw-MIME
            message = AnymailInboundMessage.parse_raw_mime(request.POST['body-mime'])
        else:
            # Fully-parsed
            message = self.message_from_mailgun_parsed(request)

        message.envelope_sender = request.POST.get('sender', None)
        message.envelope_recipient = request.POST.get('recipient', None)
        message.stripped_text = request.POST.get('stripped-text', None)
        message.stripped_html = request.POST.get('stripped-html', None)

        message.spam_detected = message.get('X-Mailgun-Sflag', 'No').lower() == 'yes'
        try:
            message.spam_score = float(message['X-Mailgun-Sscore'])
        except (TypeError, ValueError):
            pass

        return AnymailInboundEvent(
            event_type=EventType.INBOUND,
            timestamp=datetime.fromtimestamp(int(request.POST['timestamp']), tz=utc),
            event_id=request.POST.get('token', None),
            esp_event=esp_event,
            message=message,
        )

    def message_from_mailgun_parsed(self, request):
        """Construct a Message from Mailgun's "fully-parsed" fields"""
        # Mailgun transcodes all fields to UTF-8 for "fully parsed" messages
        try:
            attachment_count = int(request.POST['attachment-count'])
        except (KeyError, TypeError):
            attachments = None
        else:
            # Load attachments from posted files: Mailgun file field names are 1-based
            att_ids = ['attachment-%d' % i for i in range(1, attachment_count+1)]
            att_cids = {  # filename: content-id (invert content-id-map)
                att_id: cid for cid, att_id
                in json.loads(request.POST.get('content-id-map', '{}')).items()
            }
            attachments = [
                AnymailInboundMessage.construct_attachment_from_uploaded_file(
                    request.FILES[att_id], content_id=att_cids.get(att_id, None))
                for att_id in att_ids
            ]

        return AnymailInboundMessage.construct(
            headers=json.loads(request.POST['message-headers']),  # includes From, To, Cc, Subject, etc.
            text=request.POST.get('body-plain', None),
            html=request.POST.get('body-html', None),
            attachments=attachments,
        )