Create chunks, strata in cache via temporary files

This avoids problems with files with the right names but partial
content, if morph is killed in the middle of writing the file.

1 files changed, 17 insertions, 0 deletions

diff --git a/morphlib/cachedir.py b/morphlib/cachedir.py
index cc528a43..d0763c4c 100644
--- a/morphlib/cachedir.py
+++ b/morphlib/cachedir.py
@@ -17,6 +17,8 @@
 import hashlib
 import os
 
+import morphlib
+
 
 class CacheDir(object):
 
@@ -62,3 +64,18 @@ class CacheDir(object):
 
         return os.path.join(self.dirname, key + suffix)
 
+    def open(self, relative_name):
+        '''Open a file for writing in the cache.
+        
+        The file will be written with a temporary name, and renamed to
+        the final name when the file is closed. Additionally, if the
+        caller decides, mid-writing, that they don't want to write the
+        file after all (e.g., a log file), then the ``abort`` method
+        in the returned file handle can be called to remove the
+        temporary file.
+        
+        '''
+        
+        path = os.path.join(self.dirname, relative_name)
+        return morphlib.savefile.SaveFile(path, 'w')
+