Fix edge case of server tags unescaping, when the backslash is followed by an 'invalid' char.

src/ircmsgs.py

@@ -63,8 +63,19 @@ SERVER_TAG_ESCAPE = [
     ]
 escape_server_tag_value = utils.str.MultipleReplacer(
         dict(SERVER_TAG_ESCAPE))
-unescape_server_tag_value = utils.str.MultipleReplacer(
-        dict(map(lambda x:(x[1],x[0]), SERVER_TAG_ESCAPE)))
+
+_server_tag_unescape = {k: v for (v, k) in SERVER_TAG_ESCAPE}
+_escape_sequence_pattern = re.compile(r'\\.?')
+def _unescape_replacer(m):
+    escape_sequence = m.group(0)
+    unescaped = _server_tag_unescape.get(escape_sequence)
+    if unescaped is None:
+        # Matches both a lone \ at the end and a \ followed by an "invalid"
+        # character. In both cases, the \ must be dropped.
+        return escape_sequence[1:]
+    return unescaped
+def unescape_server_tag_value(s):
+    return _escape_sequence_pattern.sub(_unescape_replacer, s)
 
 def parse_server_tags(s):
     server_tags = {}

test/test_ircmsgs.py

@@ -163,6 +163,24 @@ class IrcMsgTestCase(SupyTestCase):
         m._str = None  # Clear the cache (set before parsing)
         self.assertEqual(str(m), s + '\r\n')
 
+        # bar\1 is equivalent to baz1
+        s = r'@foo=;bar=baz\1;qux= ' \
+            r':nick!ident@host.com PRIVMSG me :Hello'
+        m = ircmsgs.IrcMsg(s)
+        self.assertEqual(m.server_tags, {
+            'foo': None,
+            'bar': 'baz1',
+            'qux': None})
+
+        # bar\ is equivalent to baz
+        s = r'@foo=;bar=baz\;qux= ' \
+            r':nick!ident@host.com PRIVMSG me :Hello'
+        m = ircmsgs.IrcMsg(s)
+        self.assertEqual(m.server_tags, {
+            'foo': None,
+            'bar': 'baz',
+            'qux': None})
+
         s = r'@foo=;bar=baz;qux= ' \
             r':nick!ident@host.com PRIVMSG me :Hello'
         m = ircmsgs.IrcMsg(s)