Normalizer inode and device numbers. This is necessary so that

if a directory tree is moved to a new disk, the manifest doesn't
change.

1 files changed, 54 insertions, 3 deletions

diff --git a/summainlib.py b/summainlib.py
index 29ae21e..31b42a7 100644
--- a/summainlib.py
+++ b/summainlib.py
@@ -23,6 +23,57 @@ import time
 import urllib
 
 
+class NumberNormalizer(object):
+
+    '''Normalize inode and device numbers.
+    
+    When we make two manifests of the same directory tree, but the
+    tree may have been moved to another disk, the inode and device
+    numbers may be different. This should not be a cause for concern,
+    however. What is important is that if two names were hardlinked
+    to the same file before, they still are, and if they weren't,
+    they still aren't.
+    
+    To achieve this, we normalize the inode and device numbers.
+    The input files are fed to the normalizer in a deterministic
+    sequence, and the sequence defines the numbers we use. Thus,
+    if the input files have inode numbers [42, 13, 105], we produce
+    [1, 2, 3]. If one of the input numbers is repeated, that number
+    is re-used.
+    
+    This is not a perfect solution. If the second manifest has a
+    new file, it will throw off the entire remaining sequence, causing
+    a big diff. But we'll live with that.
+    
+    '''
+    
+    def __init__(self):
+        self.reset()
+
+    def get(self, input_number, numbers, next):
+        if input_number in numbers:
+            return numbers[input_number], next
+        else:
+            numbers[input_number] = next
+            return numbers[input_number], next + 1
+    
+    def get_ino(self, ino):
+        output, self.next_ino = self.get(ino, self.ino_numbers, self.next_ino)
+        return output
+    
+    def get_dev(self, dev):
+        output, self.next_dev = self.get(dev, self.dev_numbers, self.next_dev)
+        return output
+
+    def reset(self):
+        '''This is used by unit tests.'''
+        self.ino_numbers = dict()
+        self.next_ino = 1
+
+        self.dev_numbers = dict()
+        self.next_dev = 1
+
+
 class FilesystemObject(object):
 
     '''An object in the file system.
@@ -34,7 +85,7 @@ class FilesystemObject(object):
     
     '''
     
-    def __init__(self, filename, stat_result=None, sha1=None,
+    def __init__(self, filename, normalizer, stat_result=None, sha1=None,
                  open_file=None, readlink=None):
         stat_result = stat_result or os.lstat(filename)
         sha1 = sha1 or hashlib.sha1()
@@ -45,8 +96,8 @@ class FilesystemObject(object):
         self['Name'] = filename
         self['Mtime'] = self.format_time(stat_result.st_mtime)
         self['Mode'] = '%o' % stat_result.st_mode
-        self['Ino'] = '%d' % stat_result.st_ino
-        self['Dev'] = '%d' % stat_result.st_dev
+        self['Ino'] = '%d' % normalizer.get_ino(stat_result.st_ino)
+        self['Dev'] = '%d' % normalizer.get_dev(stat_result.st_dev)
         self['Nlink'] = '%d' % stat_result.st_nlink
         self['Size'] = '%d' % stat_result.st_size
         self['Uid'] = '%d' % stat_result.st_uid