Implement min/max list length validation (#3722)

Author: ipspace

docs/dev/validation-types.txt

@@ -66,7 +66,9 @@ When an attribute has a data type defined with the **type** attribute, you can u
 | **list**  | **valid_values** -- list of valid values, checked for every element in the list |
 |           | **create_empty** (bool) -- replace None value with an empty list |
 |           | **empty** (bool, default: True) -- can the list be empty? |
-|           | **make_list** (bool) -- force non-scalar values to become single-element lists |
+|           | **make_list** (bool) -- force non-scalar values to become single-element lists[^SLE] |
+|           | **min_length** (int) -- minimum list length |
+|           | **max_length** (int) -- maximum list length |
 |           | **split_lines** (bool) -- split multi-line string value into multiple list elements |
 |           | **_subtype** -- validate values as belonging to the specified subtype |
 | **dict**  | **create_empty** (bool) -- replace None value with an empty dictionary |
@@ -82,6 +84,8 @@ When an attribute has a data type defined with the **type** attribute, you can u
 | **ipv4**  | **use** -- [the use of IPv4 address/prefix](validation-ip-address) |
 | **ipv6**  | **use** -- [the use of IPv6 address/prefix](validation-ip-address) |
 
+[^SLE]: Scalar values are automatically converted to single-element lists
+
 **Notes**
 * **_keys** attribute is rarely used in dictionary definitions. Using a [shortcut definition](validation-shortcut-type) is much better. See [examples](validation-definition-examples) for a counterexample.
 

netsim/data/types.py

@@ -447,15 +447,22 @@ def must_be_list(
       value: typing.Any,
       make_list: bool = False,                          # Make anything (not just scalars) into a list
       split_lines: bool = False,                        # Split lines in a string into list items
-      empty: bool = True) -> dict:                      # Is it OK to have an empty list?
-
+      empty: bool = True,                               # Is it OK to have an empty list?
+      min_length: typing.Optional[int] = None,          # Minimum...
+      max_length: typing.Optional[int] = None           # ... and maximum list length
+        ) -> dict:
   def transform_to_list(value: typing.Any) -> list:
     if isinstance(value,str) and split_lines:
       return value.rstrip().split("\n")
 
     return [ value ]
 
   if isinstance(value,list):                            # A list is what we want to have ;)
+    if min_length is not None and len(value) < min_length:    
+      return { '_value': f'a list with at least {min_length} elements'}
+    if max_length is not None and len(value) > max_length:
+      return { '_value': f'a list with at most {max_length} elements'}
+
     if not empty and not value:                         # Do we have an unacceptable empty list?
       return { '_value': 'a scalar or a non-empty list'}
 
@@ -466,6 +473,9 @@ def transform_to_list(value: typing.Any) -> list:
   # is tied to the argument value passed to this function (it's a magic
   # transfer of hidden variables)
   #
+  if min_length is not None and min_length >= 2:
+    return { '_type': f'a list with at least {min_length} elements' }
+
   if isinstance(value,(str,int,float,bool)):
     return { '_valid': True, '_transform': transform_to_list }
 

tests/coverage/errors/attr-empty-list.log

@@ -0,0 +1,10 @@
+IncorrectType in nodes: attribute 'nodes.n1.no_empty[1]' must be a scalar or a list, found NoneType
+... use 'netlab show attributes node' to display valid attributes
+IncorrectType in nodes: attribute 'nodes.n1.not_empty[1]' must be a scalar or a list, found NoneType
+IncorrectValue in nodes: attribute 'nodes.n1.not_empty[4]' must be a scalar or a non-empty list
+IncorrectType in nodes: attribute 'nodes.n1.empty[1]' must be a scalar or a list, found NoneType
+IncorrectType in nodes: attribute 'nodes.n1.regular[3]' must be a scalar or a list, found dictionary
+IncorrectType in nodes: attribute 'nodes.n1.min2[1]' must be a list with at least 2 elements, found str
+IncorrectValue in nodes: attribute 'nodes.n1.min2[2]' must be a list with at least 2 elements
+IncorrectValue in nodes: attribute 'nodes.n1.max3[3]' must be a list with at most 3 elements
+Fatal error in netlab: Cannot proceed beyond this point due to errors, exiting

tests/coverage/errors/attr-empty-list.yml

@@ -0,0 +1,73 @@
+module: [ isis, sr ]
+defaults.device: none
+
+defaults.attributes.node:
+  no_empty:
+    type: list
+    _subtype:
+      type: list
+      create_empty: False
+  not_empty:
+    type: list
+    _subtype:
+      type: list
+      empty: False
+  empty:
+    type: list
+    _subtype:
+      type: list
+      empty: True
+      create_empty: False
+  regular:
+    type: list
+    _subtype: list
+  regular_force:
+    type: list
+    _subtype:
+      type: list
+      make_list: True
+  min2:
+    type: list
+    _subtype:
+      type: list
+      min_length: 2
+  max3:
+    type: list
+    _subtype:
+      type: list
+      max_length: 3
+nodes:
+  n1:
+    no_empty:
+    - Null              # Invalid, will not create an empty list
+    - a
+    - [ a ]
+    not_empty:
+    - Null              # Invalid, the list cannot be empty
+    - False
+    - a
+    - []                # Invalid, the list cannot be empty
+    - [ b ]
+    empty:
+    - Null              # Invalid, empty list is not created
+    - False             # ... but it can have a single False element
+    - []
+    - a
+    - [ b ]
+    regular:
+    - a
+    - [ b ]
+    - { c: d }          # Dict cannot be turned into a list
+    regular_force:      # Everything OK, dict is forced into a list
+    - Null
+    - a
+    - [ b ]
+    - { c: d }
+    min2:
+    - a                 # Cannot convert scalar into list with at least 2 elements
+    - [ a ]             # Too short
+    - [ a, b ]
+    max3:
+    - a
+    - [ a ]
+    - [ a, b, c, d ]    # Too long