[tor-commits] [stem/master] Internal _content_range() helper

[atagar at torproject.org]

commit f816134a0623cf464282ae1053e58edf312aa7a7
Author: Damian Johnson <atagar at torproject.org>
Date:   Thu Nov 15 10:18:16 2018 -0800

    Internal _content_range() helper
    
    Our new digest type and encoding arguments make our _digest_for_content()
    helper a poor fit. The only useful thing this helper does is narrow our
    content to a specific range. As such adding a helper that does only that.
    
    This doesn't yet change any of our _digest_for_content() callers. That's
    next.
---
 stem/descriptor/__init__.py | 39 +++++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/stem/descriptor/__init__.py b/stem/descriptor/__init__.py
index cf661c58..07ed5b1b 100644
--- a/stem/descriptor/__init__.py
+++ b/stem/descriptor/__init__.py
@@ -929,19 +929,38 @@ class Descriptor(object):
     :raises: ValueError if the digest canot be calculated
     """
 
-    raw_descriptor = self.get_bytes()
+    digest_content = self._content_range(start, end)
+    digest_hash = hashlib.sha1(stem.util.str_tools._to_bytes(digest_content))
+    return stem.util.str_tools._to_unicode(digest_hash.hexdigest().upper())
 
-    start_index = raw_descriptor.find(start)
-    end_index = raw_descriptor.find(end, start_index)
+  def _content_range(self, start = None, end = None):
+    """
+    Provides the descriptor content inclusively between two substrings.
 
-    if start_index == -1:
-      raise ValueError("Digest is for the range starting with '%s' but that isn't in our descriptor" % start)
-    elif end_index == -1:
-      raise ValueError("Digest is for the range ending with '%s' but that isn't in our descriptor" % end)
+    :param bytes start: start of the content range to get
+    :param bytes end: end of the content range to get
 
-    digest_content = raw_descriptor[start_index:end_index + len(end)]
-    digest_hash = hashlib.sha1(stem.util.str_tools._to_bytes(digest_content))
-    return stem.util.str_tools._to_unicode(digest_hash.hexdigest().upper())
+    :raises: ValueError if either the start or end substring are not within our content
+    """
+
+    content = self.get_bytes()
+    start_index, end_index = None, None
+
+    if start is not None:
+      start_index = content.find(start)
+
+      if start_index == -1:
+        raise ValueError("'%s' is not present within our descriptor content" % start)
+
+    if end is not None:
+      end_index = content.find(end, start_index)
+
+      if end_index == -1:
+        raise ValueError("'%s' is not present within our descriptor content" % end)
+
+      end_index += len(end)  # make the ending index inclusive
+
+    return content[start_index:end_index]
 
   def __getattr__(self, name):
     # We can't use standard hasattr() since it calls this function, recursing.