frr: return AS0 if AS_PATH length is zero

Local prefixes usually do not have an AS_PATH:
```
vtysh -c "show bgp ipv4 unicast 10.10.10.10 json" | jq '.paths[].aspath'
{
  "string": "Local",
  "segments": [],
  "length": 0
}
```

Set AS0 as a temporary solution when AS_PATH length is zero. This
avoids parser failures for local prefixes, though ideally we should
use the device's actual ASN (see TODO in code).

Signed-off-by: Tan Siewert <[email protected]>

Author: sinuscosinustan

hyperglass/models/parsing/frr.py

@@ -65,7 +65,15 @@ class FRRPath(_FRRBase):
     def validate_path(cls, values):
         """Extract meaningful data from FRR response."""
         new = values.copy()
-        new["aspath"] = values["aspath"]["segments"][0]["list"]
+        # Local prefixes (i.e. those in the same ASN) usually have
+        # no AS_PATH.
+        # Set AS_PATH to AS0 for now as we cannot ensure that the
+        # ASN for the prefix is the primary ASN.
+        if values["aspath"]["length"] != 0:
+            new["aspath"] = values["aspath"]["segments"][0]["list"]
+        else:
+            # TODO: Get an ASN that is reasonable (e.g. primary ASN)
+            new["aspath"] = [0]
         community = values.get("community", {"list": []})
         new["community"] = community["list"]
         new["lastUpdate"] = values["lastUpdate"]["epoch"]