Remove args from Features

`args` and `value` are a duplication for most of the features:
`args = [value]`
get rid of `args` and introduce `value` for `Feature` (the main class
instead of the subclasses). This makes the code simpler.

Refactoring the `freeze_serialize` function to not use an array would
simplify the code a bit more, but that needs a bit more of work.

capa/features/__init__.py

@@ -21,28 +21,28 @@ def hex_string(h):
 
 
 class Feature(object):
-    def __init__(self, args, description=None):
+    def __init__(self, value, description=None):
         super(Feature, self).__init__()
         self.name = self.__class__.__name__.lower()
-        self.args = args
+        self.value = value
         self.description = description
 
     def __hash__(self):
-        return hash((self.name, tuple(self.args)))
+        return hash((self.name, self.value))
 
     def __eq__(self, other):
-        return self.name == other.name and self.args == other.args
+        return self.name == other.name and self.value == other.value
 
-    # Used to overwrite the rendering of the feature args in `__str__` and the
+    # Used to overwrite the rendering of the feature value in `__str__` and the
     # json output
-    def get_args_str(self):
-        return ",".join(self.args)
+    def get_value_str(self):
+        return self.value
 
     def __str__(self):
         if self.description:
-            return "%s(%s = %s)" % (self.name, self.get_args_str(), self.description)
+            return "%s(%s = %s)" % (self.name, self.get_value_str(), self.description)
         else:
-            return "%s(%s)" % (self.name, self.get_args_str())
+            return "%s(%s)" % (self.name, self.get_value_str())
 
     def __repr__(self):
         return str(self)
@@ -54,7 +54,7 @@ class Feature(object):
         return self.__dict__
 
     def freeze_serialize(self):
-        return (self.__class__.__name__, self.args)
+        return (self.__class__.__name__, [self.value])
 
     @classmethod
     def freeze_deserialize(cls, args):
@@ -62,16 +62,14 @@ class Feature(object):
 
 
 class MatchedRule(Feature):
-    def __init__(self, rule_name, description=None):
-        super(MatchedRule, self).__init__([rule_name], description)
+    def __init__(self, value, description=None):
+        super(MatchedRule, self).__init__(value, description)
         self.name = "match"
-        self.rule_name = rule_name
 
 
 class Characteristic(Feature):
     def __init__(self, value, description=None):
-        super(Characteristic, self).__init__([value], description)
-        self.value = value
+        super(Characteristic, self).__init__(value, description)
 
     def freeze_serialize(self):
         # in an older version of capa, characteristics could theoretically match non-existence (value=False).
@@ -89,14 +87,12 @@ class Characteristic(Feature):
 
 class String(Feature):
     def __init__(self, value, description=None):
-        super(String, self).__init__([value], description)
-        self.value = value
+        super(String, self).__init__(value, description)
 
 
 class Bytes(Feature):
     def __init__(self, value, description=None):
-        super(Bytes, self).__init__([value], description)
-        self.value = value
+        super(Bytes, self).__init__(value, description)
 
     def evaluate(self, ctx):
         for feature, locations in ctx.items():
@@ -108,11 +104,11 @@ class Bytes(Feature):
 
         return capa.engine.Result(False, self, [])
 
-    def get_args_str(self):
+    def get_value_str(self):
         return hex_string(bytes_to_str(self.value))
 
     def freeze_serialize(self):
-        return (self.__class__.__name__, [bytes_to_str(x).upper() for x in self.args])
+        return (self.__class__.__name__, [bytes_to_str(self.value).upper()])
 
     @classmethod
     def freeze_deserialize(cls, args):

capa/features/basicblock.py

@@ -3,7 +3,14 @@ from capa.features import Feature
 
 class BasicBlock(Feature):
     def __init__(self):
-        super(BasicBlock, self).__init__([])
+        super(BasicBlock, self).__init__(None)
 
     def __str__(self):
         return "basic block"
+
+    def freeze_serialize(self):
+        return (self.__class__.__name__, [])
+
+    @classmethod
+    def freeze_deserialize(cls, args):
+        return cls()

capa/features/file.py

@@ -4,19 +4,16 @@ from capa.features import Feature
 class Export(Feature):
     def __init__(self, value, description=None):
         # value is export name
-        super(Export, self).__init__([value], description)
-        self.value = value
+        super(Export, self).__init__(value, description)
 
 
 class Import(Feature):
     def __init__(self, value, description=None):
         # value is import name
-        super(Import, self).__init__([value], description)
-        self.value = value
+        super(Import, self).__init__(value, description)
 
 
 class Section(Feature):
     def __init__(self, value, description=None):
         # value is section name
-        super(Section, self).__init__([value], description)
-        self.value = value
+        super(Section, self).__init__(value, description)

capa/features/insn.py

@@ -8,28 +8,25 @@ class API(Feature):
             modname, impname = name.split(".")
             name = modname.lower() + "." + impname
 
-        super(API, self).__init__([name], description)
+        super(API, self).__init__(name, description)
 
 
 class Number(Feature):
     def __init__(self, value, description=None):
-        super(Number, self).__init__([value], description)
-        self.value = value
+        super(Number, self).__init__(value, description)
 
-    def get_args_str(self):
+    def get_value_str(self):
         return "0x%X" % self.value
 
 
 class Offset(Feature):
     def __init__(self, value, description=None):
-        super(Offset, self).__init__([value], description)
-        self.value = value
+        super(Offset, self).__init__(value, description)
 
-    def get_args_str(self):
+    def get_value_str(self):
         return "0x%X" % self.value
 
 
 class Mnemonic(Feature):
     def __init__(self, value, description=None):
-        super(Mnemonic, self).__init__([value], description)
-        self.value = value
+        super(Mnemonic, self).__init__(value, description)

capa/render/__init__.py

@@ -85,7 +85,7 @@ def convert_feature_to_result_document(feature):
             "type": "characteristic"
         },
     """
-    result = {"type": feature.name, feature.name: feature.get_args_str()}
+    result = {"type": feature.name, feature.name: feature.get_value_str()}
     if feature.description:
         result["description"] = feature.description
 

capa/rules.py

@@ -423,7 +423,7 @@ class Rule(object):
 
         def rec(statement):
             if isinstance(statement, capa.features.MatchedRule):
-                # we're not sure at this point if the `statement.rule_name` is
+                # we're not sure at this point if the `statement.value` is
                 #  really a rule name or a namespace name (we use `MatchedRule` for both cases).
                 # we'll give precedence to namespaces, and then assume if that does work,
                 #  that it must be a rule name.
@@ -431,12 +431,12 @@ class Rule(object):
                 # we don't expect any collisions between namespaces and rule names, but its possible.
                 # most likely would be collision between top level namespace (e.g. `host-interaction`) and rule name.
                 # but, namespaces tend to use `-` while rule names use ` `. so, unlikely, but possible.
-                if statement.rule_name in namespaces:
+                if statement.value in namespaces:
                     # matches a namespace, so take precedence and don't even check rule names.
-                    deps.update(map(lambda r: r.name, namespaces[statement.rule_name]))
+                    deps.update(map(lambda r: r.name, namespaces[statement.value]))
                 else:
                     # not a namespace, assume its a rule name.
-                    deps.add(statement.rule_name)
+                    deps.add(statement.value)
 
             elif isinstance(statement, Statement):
                 for child in statement.get_children():