demo: show default route on the route graph

This is useful because the default one is not always the same as the route
to the registry.

Before, arrows were filled dot. Now only the default one is filled.

demo/demo

@@ -247,17 +247,18 @@ def node_by_ll(addr):
                     _ll[a] = n, t
     return _ll[addr]
 
-def route_svg(z=4):
+def route_svg(z = 4, default = type('', (), {'short': None})):
     graph = {}
     for n in nodes:
         g = graph[n] = defaultdict(list)
         for r in n.get_routes():
-            if r.prefix and r.prefix.startswith('2001:db8:'):
+            if r.prefix is None or r.prefix.startswith('2001:db8:'):
                 try:
-                    g[node_by_ll(r.nexthop)].append(node_by_ll(r.prefix)[0])
+                    g[node_by_ll(r.nexthop)].append(
+                        node_by_ll(r.prefix)[0] if r.prefix else default)
                 except KeyError:
                     pass
-    gv = ["digraph { splines = true; edge[color=grey, labelangle=0, arrowhead=dot];"]
+    gv = ["digraph { splines = true; edge[color=grey, labelangle=0];"]
     N = len(nodes)
     a = 2 * math.pi / N
     edges = set()
@@ -270,17 +271,23 @@ def route_svg(z=4):
             l.append((min(j, N - j), p, r))
         for j, (l, (p, t), r) in enumerate(sorted(l)):
             l = []
+            arrowhead = 'odot'
             for r in sorted(r.short for r in r):
+                if r:
                     if r == p.short:
                         r = '<font color="grey">%s</font>' % r
                     l.append(r)
+                else:
+                    arrowhead = 'dot'
             if (n.name, p.name) in edges:
                 r = 'penwidth=0'
             else:
                 edges.add((p.name, n.name))
                 r = 'style=solid' if t else 'style=dashed'
-            gv.append('%s -> %s [labeldistance=%u, headlabel=<%s>, %s];'
-                % (p.name, n.name, 1.5 * math.sqrt(j) + 2, ','.join(l), r))
+            gv.append(
+                '%s -> %s [labeldistance=%u, headlabel=<%s>, arrowhead=%s, %s];'
+                % (p.name, n.name, 1.5 * math.sqrt(j) + 2, ','.join(l),
+                   arrowhead, r))
     gv.append('}\n')
     return subprocess.Popen(('neato', '-Tsvg'),
         stdin=subprocess.PIPE, stdout=subprocess.PIPE,