T2719: prototype of an op mode command runner

based on type hints and introspection

1 files changed, 123 insertions, 0 deletions

diff --git a/python/vyos/opmode.py b/python/vyos/opmode.py
new file mode 100644
index 000000000..c0812c7fd
--- /dev/null
+++ b/python/vyos/opmode.py
@@ -0,0 +1,123 @@
+# Copyright 2022 VyOS maintainers and contributors <maintainers@vyos.io>
+#
+# This library is free software; you can redistribute it and/or
+# modify it under the terms of the GNU Lesser General Public
+# License as published by the Free Software Foundation; either
+# version 2.1 of the License, or (at your option) any later version.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+# Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public
+# License along with this library.  If not, see <http://www.gnu.org/licenses/>.
+
+import typing
+
+
+def _is_op_mode_function_name(name):
+    from re import match
+
+    if match(r"^(show|clear|reset|restart)", name):
+        return True
+    else:
+        return False
+
+def _is_show(name):
+    from re import match
+
+    if match(r"^show", name):
+        return True
+    else:
+        return False
+
+def _get_op_mode_functions(module):
+    from inspect import getmembers, isfunction
+
+    # Get all functions in that module
+    funcs = getmembers(module, isfunction)
+
+    # getmembers returns (name, func) tuples
+    funcs = list(filter(lambda ft: _is_op_mode_function_name(ft[0]), funcs))
+
+    funcs_dict = {}
+    for (name, thunk) in funcs:
+        funcs_dict[name] = thunk
+
+    return funcs_dict
+
+def _is_optional_type(t):
+    # Optional[t] is internally an alias for Union[t, NoneType]
+    # and there's no easy way to get union members it seems
+    if (type(t) == typing._UnionGenericAlias):
+        if (len(t.__args__) == 2):
+            if t.__args__[1] == type(None):
+                return True
+
+    return False
+
+def _get_arg_type(t):
+    """ Returns the type itself if it's a primitive type,
+        or the "real" type of typing.Optional
+
+       Doesn't work with anything else at the moment!
+    """
+    if _is_optional_type(t):
+        t.__args__[0]
+    else:
+        return t
+
+def run(module):
+    from argparse import ArgumentParser
+
+    functions = _get_op_mode_functions(module)
+
+    parser = ArgumentParser()
+    subparsers = parser.add_subparsers(dest="subcommand")
+
+    for function_name in functions:
+        subparser = subparsers.add_parser(function_name, help=functions[function_name].__doc__)
+
+        type_hints = typing.get_type_hints(functions[function_name])
+        for opt in type_hints:
+            th = type_hints[opt]
+
+            # Show commands require an option to choose between raw JSON and human-readable
+            # formatted output.
+            # For interactive use, they default to formatted output.
+            if (function_name == "show") and (opt == "raw"):
+                subparser.add_argument(f"--raw",  action='store_true')
+            elif _is_optional_type(th):
+                subparser.add_argument(f"--{opt}", type=_get_arg_type(th), default=None)
+            else:
+                subparser.add_argument(f"--{opt}", type=_get_arg_type(th), required=True)
+
+    # Get options as a dict rather than a namespace,
+    # so that we can modify it and pack for passing to functions
+    args = vars(parser.parse_args())
+
+    func = functions[args["subcommand"]]
+
+    # Remove the subcommand from the arguments,
+    # it would cause an extra argument error when we pass the dict to a function
+    del args["subcommand"]
+
+    if "raw" not in args:
+        args["raw"] = False
+
+    if function_name == "show":
+        # Show commands are slightly special:
+        # they may return human-formatted output
+        # or a raw dict that we need to serialize in JSON for printing
+        res = func(**args)
+        if not args["raw"]:
+            return res
+        else:
+            from json import dumps
+            return dumps(res, indent=4)
+    else:
+        # Other functions should not return anything,
+        # although they may print their own warnings or status messages
+        func(**args)
+