email: dns: Show table for desired DNS entries

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/email/dns.py

@@ -0,0 +1,68 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""
+Manage DNS entries needed for an email server.
+"""
+
+from dataclasses import dataclass
+from typing import Union
+
+from plinth.errors import ActionError
+
+
+@dataclass
+class Entry:  # pylint: disable=too-many-instance-attributes
+    """A DNS entry."""
+    type_: str
+    value: str
+    domain: Union[str, None] = None
+    class_: str = 'IN'
+    ttl: int = 60
+    priority: int = 10
+    weight: Union[int, None] = None
+    port: Union[int, None] = None
+
+    def get_split_value(self):
+        """If the record is TXT and value > 255, split it."""
+        if len(self.value) <= 255:
+            return self.value
+
+        pieces = []
+        value = self.value
+        while value:
+            pieces.append(f'"{value[:255]}"')
+            value = value[255:]
+
+        return ' '.join(pieces)
+
+
+def get_entries():
+    """Return the list of DNS entries to make."""
+    from . import audit
+
+    domain = audit.domain.get_domains()['primary_domain']
+    mx_spam_entries = [
+        Entry(type_='MX', value=f'{domain}.'),
+        Entry(type_='TXT', value='v=spf1 mx a ~all'),
+        Entry(
+            domain='_dmarc', type_='TXT',
+            value='v=DMARC1; p=none; sp=quarantine; '
+            f'rua=mailto:postmaster@{domain}; ')
+    ]
+    try:
+        dkim_public_key = audit.dkim.get_public_key(domain)
+        dkim_entries = [
+            Entry(domain='dkim._domainkey', type_='TXT',
+                  value=f'v=DKIM1; k=rsa; p={dkim_public_key}')
+        ]
+    except ActionError:
+        dkim_entries = []
+
+    autoconfig_entries = [
+        Entry(domain='_submission._tcp', type_='SRV', weight=10, port=587,
+              value=f'{domain}.'),
+        Entry(domain='_imaps._tcp', type_='SRV', weight=10, port=993,
+              value=f'{domain}.'),
+        Entry(domain='_pop3s._tcp', type_='SRV', priority=20, weight=10,
+              port=995, value=f'{domain}.'),
+    ]
+    return mx_spam_entries + dkim_entries + autoconfig_entries

plinth/modules/email/templates/email.html

@@ -15,3 +15,47 @@
     {% trans "Manage Aliases" %}
   </a>
 {% endblock %}
+
+{% block extra_content %}
+  {{ block.super }}
+
+  <h3>{% trans "DNS Records" %}</h3>
+
+  <p>
+    {% blocktrans trimmed %}
+      The following DNS records must be added manually on your primary domain
+      for the mail server to work properly.
+    {% endblocktrans %}
+  </p>
+
+  <div class="table-responsive">
+    <table class="table table-sm">
+      <thead>
+        <tr>
+          <th>{% trans "Domain" %}</th>
+          <th>{% trans "TTL" %}</th>
+          <th>{% trans "Class" %}</th>
+          <th>{% trans "Type" %}</th>
+          <th>{% trans "Priority" %}</th>
+          <th>{% trans "Weight" %}</th>
+          <th>{% trans "Port" %}</th>
+          <th>{% trans "Host/Target/Value" %}</th>
+        </tr>
+      </thead>
+      <tbody>
+        {% for dns_entry in dns_entries %}
+          <tr>
+            <td>{{ dns_entry.domain|default_if_none:"" }}</td>
+            <td>{{ dns_entry.ttl }}</td>
+            <td>{{ dns_entry.class_ }}</td>
+            <td>{{ dns_entry.type_ }}</td>
+            <td>{{ dns_entry.priority }}</td>
+            <td>{{ dns_entry.weight|default_if_none:"" }}</td>
+            <td>{{ dns_entry.port|default_if_none:"" }}</td>
+            <td class="text-break">{{ dns_entry.get_split_value }}</td>
+          </tr>
+        {% endfor %}
+      </tbody>
+    </table>
+  </div>
+{% endblock %}

plinth/modules/email/views.py

@@ -9,6 +9,7 @@ from django.utils.translation import gettext_lazy as _
 from django.views.generic.base import TemplateView
 from django.views.generic.edit import FormView
 
+from plinth.modules.email import dns
 from plinth.views import AppView
 
 from . import aliases as aliases_module
@@ -21,6 +22,12 @@ class EmailAppView(AppView):
     form_class = forms.DomainForm
     template_name = 'email.html'
 
+    def get_context_data(self, **kwargs):
+        """Add additional context data for rendering the template."""
+        context = super().get_context_data(**kwargs)
+        context['dns_entries'] = dns.get_entries()
+        return context
+
     def get_initial(self):
         """Return the initial values to populate in the form."""
         initial = super().get_initial()