Prevent out of bounds error when traversing near 0.0.0.0 (fixes #29)

CHANGELOG.md

@@ -11,6 +11,10 @@ This project adheres to [CHANGELOG](http://keepachangelog.com/).
 - Filter out subdomains with an A record matching a wildcard A record
 - Official Python 3.7 support
 
+### Fixed
+- Prevent out of bounds error when expanding IPs near 0.0.0.0 or
+  255.255.255.255
+
 ## [1.2.2] - 2018-04-24
 ### Changed
 - Python 3 is now a requirement when installing via setup.py (including pip)

fierce/fierce.py

@@ -168,12 +168,13 @@ def default_expander(ip):
 
 
 def traverse_expander(ip, n=5):
-    class_c = get_class_c_network(ip)
-
-    result = [ipaddress.IPv4Address(ip + i) for i in range(-n, n + 1)]
-    result = [i for i in result if i in class_c]
+    ip = int(ip)
+    class_c_floor = ip - (ip % 256)
+    class_c_ceiling = class_c_floor + 255
 
-    return result
+    ip_min = max(ip - n, class_c_floor)
+    ip_max = min(ip + n, class_c_ceiling)
+    return [ipaddress.IPv4Address(i) for i in range(ip_min, ip_max + 1)]
 
 
 def wide_expander(ip):

tests/test_fierce.py

@@ -144,6 +144,36 @@ def test_traverse_expander_no_cross_upper_boundary(self):
 
         self.assertEqual(expected, result)
 
+    # Upper and lower bound tests are to avoid reintroducing out of
+    # bounds error from IPv4Address. (no_cross_*_boundary tests won't
+    # necessarily cover this; GitHub issue #29)
+
+    def test_traverse_expander_lower_bound_regression(self):
+        ip = ipaddress.IPv4Address('0.0.0.1')
+        expand = 2
+
+        result = fierce.traverse_expander(ip, expand)
+        expected = [
+            ipaddress.IPv4Address('0.0.0.0'),
+            ipaddress.IPv4Address('0.0.0.1'),
+            ipaddress.IPv4Address('0.0.0.2'),
+            ipaddress.IPv4Address('0.0.0.3')
+        ]
+        self.assertEqual(expected, result)
+
+    def test_traverse_expander_upper_bound_regression(self):
+        ip = ipaddress.IPv4Address('255.255.255.254')
+        expand = 2
+
+        result = fierce.traverse_expander(ip, expand)
+        expected = [
+            ipaddress.IPv4Address('255.255.255.252'),
+            ipaddress.IPv4Address('255.255.255.253'),
+            ipaddress.IPv4Address('255.255.255.254'),
+            ipaddress.IPv4Address('255.255.255.255')
+        ]
+        self.assertEqual(expected, result)
+
     def test_wide_expander_basic(self):
         ip = ipaddress.IPv4Address('192.168.1.50')