fix #139, add unit tests for tcp.parse_opts()

dpkt/tcp.py

@@ -99,14 +99,54 @@ def parse_opts(buf):
         o = ord(buf[0])
         if o > TCP_OPT_NOP:
             try:
-                l = ord(buf[1])
+                # advance buffer at least 2 bytes = 1 type + 1 length
+                l = max(2, ord(buf[1]))
                 d, buf = buf[2:l], buf[l:]
-            except ValueError:
+            except (IndexError, ValueError):
                 # print 'bad option', repr(str(buf))
                 opts.append(None)  # XXX
                 break
         else:
+            # options 0 and 1 are not followed by length byte
             d, buf = '', buf[1:]
         opts.append((o, d))
     return opts
 
+
+def test_parse_opts():
+    # normal scenarios
+    buf = '\x02\x04\x23\x00\x01\x01\x04\x02'
+    opts = parse_opts(buf)
+    assert opts == [
+        (TCP_OPT_MSS, '\x23\x00'),
+        (TCP_OPT_NOP, ''),
+        (TCP_OPT_NOP, ''),
+        (TCP_OPT_SACKOK, '')
+    ]
+
+    buf = '\x01\x01\x05\x0a\x37\xf8\x19\x70\x37\xf8\x29\x78'
+    opts = parse_opts(buf)
+    assert opts == [
+        (TCP_OPT_NOP, ''),
+        (TCP_OPT_NOP, ''),
+        (TCP_OPT_SACK, '\x37\xf8\x19\x70\x37\xf8\x29\x78')
+    ]
+
+    # test a zero-length option
+    buf = '\x02\x00\x01'
+    opts = parse_opts(buf)
+    assert opts == [
+        (TCP_OPT_MSS, ''),
+        (TCP_OPT_NOP, '')
+    ]
+
+    # test a one-byte malformed option
+    buf = '\xff'
+    opts = parse_opts(buf)
+    assert opts == [None]
+
+
+if __name__ == '__main__':
+    # Runs all the test associated with this class/file
+    test_parse_opts()
+    print 'Tests Successful...'