1 files changed, 60 insertions, 0 deletions
diff --git a/dedup/hashing.py b/dedup/hashing.py
index 1283c7e..0c786e1 100644
--- a/dedup/hashing.py
+++ b/dedup/hashing.py
@@ -1,3 +1,6 @@
+import io
+import os
+
 class HashBlacklist(object):
     """Turn a hashlib-like object into a hash that returns None for some
     blacklisted hashes instead of the real hash value.
@@ -96,6 +99,63 @@ class SuppressingHash(object):
             return SuppressingHash(self.hashobj.copy(), self.exceptions)
         return SuppressingHash(None, self.exceptions)
 
+class StoredHash(object):
+    """A hash that stores all the updates and then does all the work on the
+    hexdigest call."""
+
+    def __init__(self, digestfunc, acceptfunc=lambda _: True,
+                 sizelimit=1024*1024*16):
+        """
+        @type digestfunc: file-like -> str
+        @param digestfunc: should read the given file-like and return
+            the computed hash. The file-like can be assumed to be seekable.
+        @type acceptfunc: file-like -> bool or None
+            should read enough of file-like to determine whether the hash
+            is computable. To accept the hash, return True. To reject
+            producing a hash return False. To defer the decision until more
+            data is available return None.
+        @type sizelimit: int
+        @param sizelimit: when the content exceeds this size, reject it
+        """
+        self.digestfunc = digestfunc
+        self.acceptfunc = acceptfunc
+        self.sizelimit = sizelimit
+        self.content = io.BytesIO()
+        self.accepted = False
+
+    def update(self, data):
+        if self.content is None or not data:
+            return
+        self.content.seek(0, os.SEEK_END)
+        if self.content.tell() + len(data) > self.sizelimit:
+            self.content = None
+            return
+        self.content.write(data)
+        if not self.accepted:
+            self.content.seek(0, os.SEEK_SET)
+            ret = self.acceptfunc(self.content)
+            if ret is None:
+                return
+            if ret:
+                self.accepted = True
+            else:
+                self.content = None
+
+    def hexdigest(self):
+        if not self.content or not self.accepted:
+            return None
+        self.content.seek(0, os.SEEK_SET)
+        return self.digestfunc(self.content)
+
+    def copy(self):
+        new = StoredHash(self.digestfunc, self.acceptfunc, self.sizelimit)
+        if self.content:
+            new.content = io.BytesIO(self.content.getvalue())
+        else:
+            new.content = None
+        new.accepted = self.accepted
+        return new
+
 def hash_file(hashobj, filelike, blocksize=65536):
     """Feed the entire contents from the given filelike to the given hashobj.
     @param hashobj: hashlib-like object providing an update method