jstore: Nicer error message on non-numeric file content

An error like “invalid literal for int() with base 10” can be quite
confusing.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

lib/jstore.py

@@ -42,12 +42,19 @@ def _ReadNumericFile(file_name):
 
   """
   try:
-    return int(utils.ReadFile(file_name))
+    contents = utils.ReadFile(file_name)
   except EnvironmentError, err:
     if err.errno in (errno.ENOENT, ):
       return None
     raise
 
+  try:
+    return int(contents)
+  except (ValueError, TypeError), err:
+    # Couldn't convert to int
+    raise errors.JobQueueError("Content of file '%s' is not numeric: %s" %
+                               (file_name, err))
+
 
 def ReadSerial():
   """Read the serial file.

test/ganeti.jstore_unittest.py

@@ -78,5 +78,24 @@ class TestParseJobId(testutils.GanetiTestCase):
     self.assertRaises(errors.ParameterError, jstore.ParseJobId, [])
 
 
+class TestReadNumericFile(testutils.GanetiTestCase):
+  def testNonExistingFile(self):
+    result = jstore._ReadNumericFile("/tmp/this/file/does/not/exist")
+    self.assertTrue(result is None)
+
+  def testValidFile(self):
+    tmpfile = self._CreateTempFile()
+
+    for (data, exp) in [("123", 123), ("0\n", 0)]:
+      utils.WriteFile(tmpfile, data=data)
+      result = jstore._ReadNumericFile(tmpfile)
+      self.assertEqual(result, exp)
+
+  def testInvalidContent(self):
+    tmpfile = self._CreateTempFile()
+    utils.WriteFile(tmpfile, data="{wrong content")
+    self.assertRaises(errors.JobQueueError, jstore._ReadNumericFile, tmpfile)
+
+
 if __name__ == "__main__":
   testutils.GanetiTestProgram()