From e74405d27a63434c9114c906a7250ab59570ff93 Mon Sep 17 00:00:00 2001
From: William Grant <me@williamgrant.id.au>
Date: Sat, 12 Mar 2011 12:24:55 +1100
Subject: [PATCH] Raise more descriptive exceptions, DuplicateTag and
 InvalidTagSpec.

---
 dkim/tests/test_dkim.py | 11 ++++++-----
 dkim/util.py            | 14 ++++++++++++--
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/dkim/tests/test_dkim.py b/dkim/tests/test_dkim.py
index 4d88eef..d8d2f58 100644
--- a/dkim/tests/test_dkim.py
+++ b/dkim/tests/test_dkim.py
@@ -3,7 +3,8 @@ import unittest
 
 import dkim
 from dkim.util import (
-    InvalidTagValueList,
+    DuplicateTag,
+    InvalidTagSpec,
     parse_tag_value,
     )
 
@@ -83,13 +84,13 @@ class TestParseTagValue(unittest.TestCase):
             parse_tag_value('   foo  \t= bar;\tbaz=  f oo=bar  '))
 
     def test_missing_value_is_an_error(self):
-        self.assertRaises(
-            InvalidTagValueList,
+        self.assertRaisesRegexp(
+            InvalidTagSpec, 'baz',
             parse_tag_value, 'foo=bar;baz')
 
     def test_duplicate_tag_is_an_error(self):
-        self.assertRaises(
-            InvalidTagValueList,
+        self.assertRaisesRegexp(
+            DuplicateTag, 'foo',
             parse_tag_value, 'foo=bar;foo=baz')
 
 
diff --git a/dkim/util.py b/dkim/util.py
index b977c79..8511ca2 100644
--- a/dkim/util.py
+++ b/dkim/util.py
@@ -17,6 +17,8 @@
 # Copyright (c) 2011 William Grant <me@williamgrant.id.au>
 
 __all__ = [
+    'DuplicateTag',
+    'InvalidTagSpec',
     'InvalidTagValueList',
     'parse_tag_value',
     ]
@@ -26,6 +28,14 @@ class InvalidTagValueList(Exception):
     pass
 
 
+class DuplicateTag(InvalidTagValueList):
+    pass
+
+
+class InvalidTagSpec(InvalidTagValueList):
+    pass
+
+
 def parse_tag_value(tag_list):
     """Parse a DKIM Tag=Value list.
 
@@ -43,8 +53,8 @@ def parse_tag_value(tag_list):
         try:
             key, value = tag_spec.split('=', 1)
         except ValueError:
-            raise InvalidTagValueList()
+            raise InvalidTagSpec(tag_spec)
         if key.strip() in tags:
-            raise InvalidTagValueList()
+            raise DuplicateTag(key.strip())
         tags[key.strip()] = value.strip()
     return tags