1 files changed, 62 insertions, 0 deletions
diff --git a/obnamlib/whole_file_checksummer.py b/obnamlib/whole_file_checksummer.py
new file mode 100644
index 00000000..517c09a1
--- /dev/null
+++ b/obnamlib/whole_file_checksummer.py
@@ -0,0 +1,62 @@
+# Copyright 2016  Lars Wirzenius
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+# =*= License: GPL-3+ =*=
+
+
+import hashlib
+
+import obnamlib
+
+
+class WholeFileCheckSummer(object):
+
+    '''Compute a whole-file checksum.
+
+    Ask the repository its preferred checksum algorithm. Use that.
+
+    If the algorithm is MD5, compute the checksum from all the bytes
+    in the file. For everything else, compute the checksum from (size,
+    checksum) pairs for all the chunks in the file. This convoluted
+    thing is because the latter is necessary for speed, and the former
+    is necessary for backwards compatibilty.
+
+    '''
+
+    def __init__(self, repo):
+        self._summer = self._create_checksum_algorithm(repo)
+
+    def _create_checksum_algorithm(self, repo):
+        file_key = repo.get_file_checksum_key()
+        if file_key is None:
+            return _NullChecksum()
+        name = obnamlib.get_checksum_algorithm_name(file_key)
+        return obnamlib.get_checksum_algorithm(name)
+
+    def append_chunk(self, chunk_data, token):
+        self._summer.update(chunk_data)
+
+    def get_checksum(self):
+        '''Get the current whole-file checksum.'''
+        return self._summer.hexdigest()
+
+
+class _NullChecksum(object):
+
+    def update(self, data):
+        pass
+
+    def hexdigest(self):
+        return None