Improve missing_sessions Jinja2 filters

It should now work correctly with PeeringDB network objects by returning
all possible sessions. It does not exclude the existing ones (for now).

docs/templating/filters.md

@@ -260,6 +260,10 @@ On an autonomous system, it will return all sessions that can be configured
 between two autonomous systems. You must provide a second AS, providing an IXP
 is optional.
 
+When one of the parameters is a PeeringDB network object, e.g. when used to
+send an e-mail to an AS unknown to Peering Manager, all possible sessions will
+be returned (according to PeeringDB).
+
 Example:
 
 ```no-highlight

peering_manager/jinja2/filters.py

@@ -22,7 +22,7 @@
     Router,
 )
 from peering_manager.models.features import ConfigContextMixin, TagsMixin
-from peeringdb.functions import get_shared_facilities
+from peeringdb.functions import get_possible_peering_sessions, get_shared_facilities
 from peeringdb.models import Network
 from utils.functions import get_key_in_hash, serialize_object
 
@@ -637,17 +637,32 @@ def shared_facilities(value, other):
 def missing_sessions(value, other, ixp=None):
     """
     Returns all missing sessions between two ASNs, optionally on an IXP.
+
+    When used with a PeeringDB network record, this will return possible
+    sessions between the two networks without excluding already existing
+    sessions (known limitation).
     """
+    # Comparing two autonomous systems
+    if isinstance(value, AutonomousSystem) and isinstance(other, AutonomousSystem):
+        return value.get_missing_peering_sessions(other, internet_exchange_point=ixp)
+
+    ixlan = ixp.peeringdb_ixlan if ixp is not None else None
+
     if isinstance(value, AutonomousSystem):
-        as1 = value
-        as2 = other
-    elif isinstance(other, AutonomousSystem):
-        as1 = other
-        as2 = value
+        network_a = value.peeringdb_network
+    elif isinstance(value, Network):
+        network_a = value
+    else:
+        raise ValueError(f"{value} is not an autonomous system or a peeringdb network")
+
+    if isinstance(other, AutonomousSystem):
+        network_b = other.peeringdb_network
+    elif isinstance(other, Network):
+        network_b = other
     else:
-        raise ValueError(f"at least {value} or {other} must be an autonomous system")
+        raise ValueError(f"{other} is not an autonomous system or a peeringdb network")
 
-    return as1.get_missing_peering_sessions(as2, internet_exchange_point=ixp)
+    return get_possible_peering_sessions(network_a, network_b, ixlan=ixlan)
 
 
 def prefix_list(value, family=0):

peeringdb/functions.py

@@ -1,9 +1,9 @@
-from .models import Facility, IXLan, IXLanPrefix, NetworkFacility, NetworkIXLan
+from .models import Facility, IXLan, NetworkFacility, NetworkIXLan
 
 __all__ = (
+    "get_possible_peering_sessions",
     "get_shared_internet_exchanges",
     "get_shared_facilities",
-    "get_ixlan_prefixes",
 )
 
 
@@ -12,21 +12,38 @@ def get_shared_internet_exchanges(as1, as2):
     Returns shared IXPs (via PeeringDB IXLAN objects) between two autonomous systems
     based on PeeringDB data.
     """
-    # If both AS are the same or one of each has not PeeringDB record
+    # If both AS are the same or one of each has no PeeringDB record
     # Cannot find shared IXPs
-    if as1 == as2 or as1 is None or as2 is None:
+    if as1 is None or as2 is None or as1 == as2:
         return IXLan.objects.none()
 
     # Find IX LANs to which AS are participating to and get IDs
     ixlan_ids_1 = NetworkIXLan.objects.filter(net=as1).values_list("ixlan", flat=True)
     ixlan_ids_2 = NetworkIXLan.objects.filter(net=as2).values_list("ixlan", flat=True)
 
     # Return IXP LANs found previously
-    return IXLan.objects.filter(pk__in=ixlan_ids_1).intersection(
-        IXLan.objects.filter(pk__in=ixlan_ids_2)
+    return IXLan.objects.filter(pk__in=ixlan_ids_1) & IXLan.objects.filter(
+        pk__in=ixlan_ids_2
     )
 
 
+def get_possible_peering_sessions(as1, as2, ixlan=None):
+    # If both AS are the same or one of each has no PeeringDB record
+    # Cannot find sessions for AS1 to peer with AS2
+    if as1 is None or as2 is None or as1 == as2:
+        return NetworkIXLan.objects.none()
+
+    # Find network IX LANs of AS2 that could be used to peer with AS1
+    if ixlan:
+        ixlan_ids = NetworkIXLan.objects.filter(net=as1, ixlan=ixlan).values_list(
+            "ixlan", flat=True
+        )
+    else:
+        ixlan_ids = NetworkIXLan.objects.filter(net=as1).values_list("ixlan", flat=True)
+
+    return NetworkIXLan.objects.filter(net=as2, ixlan__in=ixlan_ids)
+
+
 def get_shared_facilities(as1, as2):
     """
     Returns shared facilities between two autonomous systems based on PeeringDB data.
@@ -40,15 +57,6 @@ def get_shared_facilities(as1, as2):
     netfac_ids_1 = NetworkFacility.objects.filter(net=as1).values_list("fac", flat=True)
     netfac_ids_2 = NetworkFacility.objects.filter(net=as2).values_list("fac", flat=True)
 
-    return Facility.objects.filter(pk__in=netfac_ids_1).intersection(
-        Facility.objects.filter(pk__in=netfac_ids_2)
+    return Facility.objects.filter(pk__in=netfac_ids_1) & Facility.objects.filter(
+        pk__in=netfac_ids_2
     )
-
-
-def get_ixlan_prefixes(ixlan):
-    """
-    Returns all prefixes used on an IXP LAN.
-    """
-    if not ixlan or not isinstance(ixlan, IXLan):
-        return IXLanPrefix.objects.none()
-    return IXLanPrefix.objects.filter(ixlan=ixlan)