[vpn] make a vpn creat-able!

[15:40] line:~% http -a nicoschottelius:$(pass ungleich.ch/nico.schottelius@ungleich.ch)  http://localhost:8000/net/vpn/ network_size=48  wireguard_public_key=$(wg genkey | wg pubkey)
HTTP/1.1 201 Created
Allow: GET, POST, HEAD, OPTIONS
Content-Length: 206
Content-Type: application/json
Date: Sun, 12 Apr 2020 13:40:26 GMT
Server: WSGIServer/0.2 CPython/3.7.3
Vary: Accept
X-Content-Type-Options: nosniff
X-Frame-Options: DENY

{
    "extra_data": null,
    "network": "2a0a:e5c1:203::",
    "order": null,
    "owner": 30,
    "status": "PENDING",
    "uuid": "8f977a8f-e06a-4346-94ae-8f525df58b7b",
    "wireguard_public_key": "JvCuUTZHm9unasJkGsLKN0Bf/hu6ZSIv7dnIGPyJ6xA="
}

uncloud_django_based/uncloud/uncloud_net/serializers.py

@@ -19,7 +19,8 @@ class VPNNetworkSerializer(serializers.ModelSerializer):
     # This is required for finding the VPN pool, but does not
     # exist in the model
     network_size = serializers.IntegerField(min_value=0,
-                                            max_value=128)
+                                            max_value=128,
+                                            write_only=True)
 
     def validate_wireguard_public_key(self, value):
         msg = _("Supplied key is not a valid wireguard public key")
@@ -58,18 +59,37 @@ class VPNNetworkSerializer(serializers.ModelSerializer):
         """
         Creating a new vpnnetwork - there are a couple of race conditions,
         especially when run in parallel.
-        """
-        pools = VPNPool.objects.filter(subnetwork_size=data['network_size'])
 
-        found_pool = False
+        What we should be doing:
+
+        - create a reservation race free
+        - map the reservation to a network (?)
+        """
+
+        pools = VPNPool.objects.filter(subnetwork_size=validated_data['network_size'])
+
+        vpn_network = None
+
         for pool in pools:
             if pool.num_free_networks > 0:
-                found_pool = True
-#                address = pool.
-#                reservation = VPNNetworkReservation(vpnpool=pool,
+                next_address = pool.next_free_network
+
+                reservation, created = VPNNetworkReservation.objects.update_or_create(
+                    vpnpool=pool, address=next_address,
+                    defaults = {
+                        'status': 'used'
+                    })
+
+                vpn_network = VPNNetwork.objects.create(
+                    owner=self.context['request'].user,
+                    network=reservation,
+                    wireguard_public_key=validated_data['wireguard_public_key']
+                )
+
+                break
+        if not vpn_network:
+            # FIXME: use correct exception
+            raise Exception("Did not find any free pool")
 
 
-        pool = VPNPool.objects.first(subnetwork_size=data['network_size'])
-
-
-        return VPNNetwork(**validated_data)
+        return vpn_network