Added method for comparing stat results to see if a file has changed since the previous backup.

2 files changed, 71 insertions, 0 deletions

diff --git a/obnam/app.py b/obnam/app.py
index f1b5a416..5612ab29 100644
--- a/obnam/app.py
+++ b/obnam/app.py
@@ -132,6 +132,22 @@ class Application:
             else:
                 i += 1
 
+    def file_is_unchanged(self, stat1, stat2):
+        """Has a file changed?
+        
+        Given the stat results from the previous generation and the
+        current file, return True if the file is identical from the
+        previous generation (i.e., no new data to back up).
+        
+        """
+        
+        fields = ("mode", "dev", "nlink", "uid", "gid", "size", "mtime")
+        for field in fields:
+            field = "st_" + field
+            if getattr(stat1, field) != getattr(stat2, field):
+                return False
+        return True
+
     def set_prevgen_filelist(self, filelist):
         """Set the Filelist object from the previous generation.
         
diff --git a/obnam/appTests.py b/obnam/appTests.py
index 24a982fb..47b64578 100644
--- a/obnam/appTests.py
+++ b/obnam/appTests.py
@@ -144,6 +144,61 @@ class ApplicationMakeFileGroupsTests(unittest.TestCase):
         self.failIf("/" in fg.get_names()[0])
 
 
+class ApplicationUnchangedFileRecognitionTests(unittest.TestCase):
+
+    def setUp(self):
+        context = obnam.context.Context()
+        self.app = obnam.Application(context)
+
+    def testSameFileWhenStatIsIdentical(self):
+        st = obnam.utils.make_stat_result()
+        self.failUnless(self.app.file_is_unchanged(st, st))
+
+    def testSameFileWhenIrrelevantFieldsChange(self):
+        st1 = obnam.utils.make_stat_result()
+        st2 = obnam.utils.make_stat_result(st_ino=42,
+                                           st_atime=42,
+                                           st_blocks=42,
+                                           st_blksize=42,
+                                           st_rdev=42)
+        self.failUnless(self.app.file_is_unchanged(st1, st2))
+
+    def testChangedFileWhenDevChanges(self):
+        st1 = obnam.utils.make_stat_result()
+        st2 = obnam.utils.make_stat_result(st_dev=42)
+        self.failIf(self.app.file_is_unchanged(st1, st2))
+
+    def testChangedFileWhenModeChanges(self):
+        st1 = obnam.utils.make_stat_result()
+        st2 = obnam.utils.make_stat_result(st_mode=42)
+        self.failIf(self.app.file_is_unchanged(st1, st2))
+
+    def testChangedFileWhenNlinkChanges(self):
+        st1 = obnam.utils.make_stat_result()
+        st2 = obnam.utils.make_stat_result(st_nlink=42)
+        self.failIf(self.app.file_is_unchanged(st1, st2))
+
+    def testChangedFileWhenUidChanges(self):
+        st1 = obnam.utils.make_stat_result()
+        st2 = obnam.utils.make_stat_result(st_uid=42)
+        self.failIf(self.app.file_is_unchanged(st1, st2))
+
+    def testChangedFileWhenGidChanges(self):
+        st1 = obnam.utils.make_stat_result()
+        st2 = obnam.utils.make_stat_result(st_gid=42)
+        self.failIf(self.app.file_is_unchanged(st1, st2))
+
+    def testChangedFileWhenSizeChanges(self):
+        st1 = obnam.utils.make_stat_result()
+        st2 = obnam.utils.make_stat_result(st_size=42)
+        self.failIf(self.app.file_is_unchanged(st1, st2))
+
+    def testChangedFileWhenMtimeChanges(self):
+        st1 = obnam.utils.make_stat_result()
+        st2 = obnam.utils.make_stat_result(st_mtime=42)
+        self.failIf(self.app.file_is_unchanged(st1, st2))
+
+
 class ApplicationFindFileByNameTests(unittest.TestCase):
 
     def setUp(self):