Limit length of filenames (#311)

* Limit length of filenames

If whipper generated filenames are longer thant the maximum value supported by the filesystem, the I/O operations are going to fail.
With this commit filenames which may be too long are truncated to the maximum allowable length.

Fixes #197.

whipper/common/common.py

@@ -23,6 +23,7 @@ import os
 import os.path
 import math
 import subprocess
+import unicodedata
 
 from whipper.extern import asyncsub
 
@@ -153,6 +154,20 @@ class MissingFrames(Exception):
     pass
 
 
+def truncate_filename(path):
+    """
+    Truncate filename to the max. len. allowed by the path's filesystem
+    Hopefully it handles Unicode strings correctly
+    """
+    p, f = os.path.split(os.path.normpath(path))
+    f, e = os.path.splitext(f)
+    fn_lim = os.pathconf(p, 'PC_NAME_MAX')  # max filenmae length in bytes
+    max = fn_lim - len(e.encode('utf-8'))
+    f = unicodedata.normalize('NFC', f)
+    f_trunc = unicode(f.encode('utf-8')[:max], 'utf-8', errors='ignore')
+    return os.path.join(p, f_trunc + e)
+
+
 def shrinkPath(path):
     """
     Shrink a full path to a shorter version.