Refactor 'interface_feature_check' in link transformation code

I thought I would need to check more features in that function, and
it was already bloated with all the IPv4 and IPv6 checks, so I
refactored it into 'ipv4 checks', 'ipv6 checks' and 'common code'.

Not only does it look nicer (and easier to read), it's also ready for
further checks. Maybe I'll eventually move the 'is RA implemented'
checks there.

Author: ipspace

netsim/augment/links.py

@@ -1030,46 +1030,53 @@ def check_link_type(data: Box) -> bool:
   return True
 
 #
-# Interface Feature Check -- validate that the selected addressing works on target lab devices
+# Interface Feature Check -- validate that the selected interface features work on target lab devices
 #
 
+def interface_fc_ipv4(ifdata: Box, ndata: Box, features: Box, more_data: str) -> None:
+  if 'ipv4' not in ifdata:
+    return
+  if ifdata.ipv4 is True:
+    f_v4_unnum = features.initial.ipv4.unnumbered
+    if not f_v4_unnum:
+      log.error(
+        text=f'Invalid unnumbered IPv4 interface {ifdata.ifname} ({ifdata.name}) on node {ndata.name} ',
+        more_hints=f'Device {ndata.device} (node {ndata.name}) does not support unnumbered IPv4 interfaces',
+        category=log.IncorrectValue,
+        module='interfaces')
+    elif isinstance(f_v4_unnum,list):
+      if ifdata.type not in features.initial.ipv4.unnumbered:
+        log.error(
+          text=f'Node {ndata.name} uses unsupported unnumbered IPv4 interface type {ifdata.type}',
+          more_data=more_data,
+          more_hints=f'Device {ndata.device} supports only {",".join(f_v4_unnum)} unnumbered IPv4 interfaces',
+          category=log.IncorrectValue,
+          module='interfaces')
+    elif f_v4_unnum == 'peer':
+      if len(ifdata.neighbors)!=1 or ifdata.neighbors[0].get('ipv4',False) is not True:
+        log.error(
+          text=f'The unnumbered IPv4 interface {ifdata.ifname} ({ifdata.name}) on node {ndata.name} is not supported',
+          more_hints=f'Device {ndata.device} can have unnumbered IPv4 interfaces with a single unnumbered peer',
+          category=log.IncorrectType,
+          module='interfaces')
+
+def interface_fc_ipv6(ifdata: Box, ndata: Box, features: Box, more_data: str) -> None:
+  if 'ipv6' not in ifdata:
+    return
+  if ifdata.ipv6 is True and not features.initial.ipv6.lla:
+    log.error(
+      f'Device {ndata.device} (node {ndata.name}) does not support LLA-only IPv6 interfaces',
+      category=log.IncorrectValue,
+      more_data=more_data,
+      module='interfaces')
+
 def interface_feature_check(nodes: Box, defaults: Box) -> None:
   for node,ndata in nodes.items():
     features = devices.get_device_features(ndata,defaults)
     for ifdata in ndata.get('interfaces',[]):
       more_data = f'Interface {ifdata.ifname} (link {ifdata.name})'
-      if 'ipv4' in ifdata:
-        if ifdata.ipv4 is True:
-          f_v4_unnum = features.initial.ipv4.unnumbered
-          if not f_v4_unnum:
-            log.error(
-              text=f'Invalid unnumbered IPv4 interface {ifdata.ifname} ({ifdata.name}) on node {node} ',
-              more_hints=f'Device {ndata.device} (node {node}) does not support unnumbered IPv4 interfaces',
-              category=log.IncorrectValue,
-              module='interfaces')
-          elif isinstance(f_v4_unnum,list):
-            if ifdata.type not in features.initial.ipv4.unnumbered:
-              log.error(
-                text=f'Node {node} uses unsupported unnumbered IPv4 interface type {ifdata.type}',
-                more_data=more_data,
-                more_hints=f'Device {ndata.device} supports only {",".join(f_v4_unnum)} unnumbered IPv4 interfaces',
-                category=log.IncorrectValue,
-                module='interfaces')
-          elif f_v4_unnum == 'peer':
-            if len(ifdata.neighbors)!=1 or ifdata.neighbors[0].get('ipv4',False) is not True:
-              log.error(
-                text=f'The unnumbered IPv4 interface {ifdata.ifname} ({ifdata.name}) on node {node} is not supported',
-                more_hints=f'Device {ndata.device} can have unnumbered IPv4 interfaces with a single unnumbered peer',
-                category=log.IncorrectType,
-                module='interfaces')
-
-      if 'ipv6' in ifdata:
-        if ifdata.ipv6 is True and not features.initial.ipv6.lla:
-          log.error(
-            f'Device {ndata.device} (node {node}) does not support LLA-only IPv6 interfaces',
-            category=log.IncorrectValue,
-            more_data=more_data,
-            module='interfaces')
+      interface_fc_ipv4(ifdata,ndata,features,more_data)
+      interface_fc_ipv6(ifdata,ndata,features,more_data)
 
 '''
 copy_link_gateway -- copy link gateway addresses to node-on-link (future interface) data