Fix ECDriverError.__str__

If ECDriverError is initialized with a non-string argument then its
str method returns non-string, it will return a confusable message
for users.

This patch fixes ECDriverError to set a string message when
the argument doesn't have str method which return a string.

pyeclib/ec_iface.py

@@ -112,8 +112,12 @@ class PyECLib_FRAGHDRCHKSUM_Types(PyECLibEnum):
 # Generic ECDriverException
 class ECDriverError(Exception):
 
-    def __init__(self, error_str):
-        self.error_str = error_str
+    def __init__(self, error):
+        try:
+            self.error_str = str(error)
+        except TypeError:
+            self.error_str = 'Error retrieving the error message from %s' \
+                % error.__class__.__name__
 
     def __str__(self):
         return self.error_str

test/test_pyeclib_api.py

@@ -26,12 +26,14 @@ from string import ascii_letters, ascii_uppercase, digits
 import sys
 import tempfile
 import unittest
+import mock
 from pyeclib.ec_iface import ECDriverError
 
 from pyeclib.ec_iface import ECDriver, VALID_EC_TYPES, ECDriverError, \
     PyECLib_EC_Types
 from test_pyeclib_c import _available_backends
 import pyeclib_c
+from pyeclib_c import error as PyECLibError
 
 if sys.version < '3':
     def b2i(b):
@@ -207,7 +209,7 @@ class TestPyECLibDriver(unittest.TestCase):
 
     def test_get_metadata_formatted(self):
         pyeclib_driver = ECDriver(k=12, m=2, ec_type="jerasure_rs_vand", chksum_type="inline_crc32")
-        
+
         filesize = 1024 * 1024 * 3
         file_str = ''.join(random.choice(ascii_letters) for i in range(filesize))
         file_bytes = file_str.encode('utf-8')
@@ -547,5 +549,45 @@ class TestPyECLibDriver(unittest.TestCase):
         self.assertTrue(
             pyeclib_drivers[0].min_parity_fragments_needed() == 1)
 
+    def test_ECDriver_error_handling(self):
+        driver = ECDriver(k=3, m=1, ec_type="jerasure_rs_vand")
+
+        class MockPyECLibError(PyECLibError):
+            def __str__(self):
+                return mock.MagicMock()
+
+        with mock.patch('pyeclib_c.decode', side_effect=MockPyECLibError()):
+            with self.assertRaises(ECDriverError) as cm:
+                driver.decode([' ' for x in xrange(4)])
+            exception = cm.exception
+            expected = 'Error retrieving the error message from MockPyECLibError'
+            self.assertEquals(expected, str(exception))
+
+    def test_ECDriverError_init(self):
+
+        class mock_class(object):
+            def __init__(self, return_str):
+                self.return_str = return_str
+
+            def __str__(self):
+                if self.return_str:
+                    return 'message'
+                else:
+                    return mock.MagicMock()
+
+        # init with str
+        error = ECDriverError('message')
+        self.assertEquals('message', str(error))
+
+        # init with instance with valid __str__
+        error = ECDriverError(mock_class(True))
+        self.assertEquals('message', str(error))
+
+        # init with instance with invalid __str__
+        error = ECDriverError(mock_class(False))
+        self.assertEquals('Error retrieving the error message from mock_class',
+                          str(error))
+
+
 if __name__ == '__main__':
     unittest.main()