fixing #1166 ... cleaner with identity list of binary methods

sarracenia/flow/__init__.py

@@ -1457,7 +1457,7 @@ def file_should_be_downloaded(self, msg) -> bool:
             method='unknown'
 
         # if no method given, then assume binary comparison is good.
-        if method in ['sha512', 'md5', 'unknown']: 
+        if method in sarracenia.identity.binary_methods: 
             if 'size' in msg:
                 end = msg['size']
                 # compare sizes... if (sr_subscribe is downloading partitions into taget file) and (target_file isn't fully done)

sarracenia/identity/__init__.py

@@ -84,6 +84,12 @@ def value(self):
 import sarracenia.identity.random
 import sarracenia.identity.sha512
 
+# the 'unknown' method is created to accomodate cases where a identity field 
+# missing, or the corresponding class is not known to this instance.
+
+# methods where size checks makes sense. updated when new methods added.
+binary_methods = [ 'sha512', 'md5', 'unknown' ]
+
 known_methods = []
 for sc in Identity.__subclasses__():
     known_methods.append(sc.__name__.lower())