statd: return empty data from run commands, drop getitem()

These changes are intended to make yanger a bit more robust.  Instead of
bailing out on command errors, we now return empty string or object back
to the callee in run_cmd() and run_json_cmd().

One example where yanger previously exited hard, and dragged with it the
entire session, is when inspecting container status or when attempting
to restart container instances which have yet to be created/stopped.

Fixes #558

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/statd/python/yanger/yanger.py

@@ -62,15 +62,6 @@ def json_get_yang_origin(addr):
     return xlate.get(proto, "other")
 
 
-def getitem(data, key):
-    """Get sub-object from an object"""
-    while key:
-        data = data[key[0]]
-        key = key[1:]
-
-    return data
-
-
 def get_proc_value(procfile):
     """Return contents of /proc file, or None"""
     try:
@@ -111,7 +102,7 @@ def insert(obj, *path_and_value):
     curr[path[-1]] = value
 
 
-def run_cmd(cmd, testfile):
+def run_cmd(cmd, testfile, default=None):
     """Run a command (array of args) and return an array of lines"""
 
     if TESTPATH and testfile:
@@ -122,10 +113,12 @@ def run_cmd(cmd, testfile):
         return output.splitlines()
     except subprocess.CalledProcessError as err:
         logger.error(f"{err}")
-        sys.exit(1)
+        if default is not None:
+            return default
+        raise
 
 
-def run_json_cmd(cmd, testfile):
+def run_json_cmd(cmd, testfile, default=None):
     """Run a command (array of args) with JSON output and return the JSON"""
 
     if TESTPATH and testfile:
@@ -138,11 +131,15 @@ def run_json_cmd(cmd, testfile):
         data = json.loads(output)
     except subprocess.CalledProcessError as err:
         logger.error(f"{err}")
-        data = {}
+        if default is not None:
+            return default
+        raise
     except json.JSONDecodeError as err:
         logger.error(f"failed parsing JSON output of command: {' '.join(cmd)}"
                      f", error: {err}")
-        sys.exit(1)
+        if default is not None:
+            return default
+        raise
     return data
 
 
@@ -466,19 +463,21 @@ def get_bridge_port_stp_state(ifname):
     return None
 
 
-def container_inspect(name, key):
-    """Call podman inspect {name}, return object at {path} or None"""
+def container_inspect(name):
+    """Call podman inspect {name}, return object at {path} or None."""
     cmd = ['podman', 'inspect', name]
-    raw = run_json_cmd(cmd, "")
-
-    return getitem(raw[0], key)
+    try:
+        return run_json_cmd(cmd, "", default=[])
+    except Exception as e:
+        logging.error(f"Error running podman inspect: {e}")
+        return []
 
 
 def add_container(containers):
     """We list *all* containers, not just those in the configuraion."""
     cmd = ['podman', 'ps', '-a', '--format=json']
 
-    raw = run_json_cmd(cmd, "")
+    raw = run_json_cmd(cmd, "", default=[])
     for entry in raw:
         running = entry["State"] == "running"
 
@@ -497,8 +496,14 @@ def add_container(containers):
 
         # The 'podman ps' command lists ports even in host mode, but
         # that's not applicable, so skip networks and port forwardings
-        networks = container_inspect(container["name"], ("NetworkSettings", "Networks"))
-        if "host" in networks:
+        cont = container_inspect(container["name"])
+        if cont and isinstance(cont, list) and len(cont) > 0:
+            cont = cont[0]
+        else:
+            cont = {}
+
+        networks = cont.get("NetworkSettings", {}).get("Networks")
+        if networks and "host" in networks:
             container["network"] = {"host": True}
         else:
             container["network"] = {