1 files changed, 85 insertions, 0 deletions
diff --git a/external/construct/protocols/layer3/ipv4.py b/external/construct/protocols/layer3/ipv4.py
new file mode 100644
index 0000000..82dfaa9
--- /dev/null
+++ b/external/construct/protocols/layer3/ipv4.py
@@ -0,0 +1,85 @@
+"""
+Internet Protocol version 4 (TCP/IP protocol stack)
+"""
+from construct import *
+import six
+from binascii import unhexlify
+
+try:
+    bytes
+except NameError:
+    bytes = str
+
+
+class IpAddressAdapter(Adapter):
+    def _encode(self, obj, context):
+        if bytes is str:
+            return "".join(chr(int(b)) for b in obj.split("."))
+        else:
+            return bytes(int(b) for b in obj.split("."))
+    def _decode(self, obj, context):
+        if bytes is str:
+            return ".".join(str(ord(b)) for b in obj)
+        else:
+            return ".".join("%d" % (b,) for b in obj)
+
+def IpAddress(name):
+    return IpAddressAdapter(Bytes(name, 4))
+
+def ProtocolEnum(code):
+    return Enum(code,
+        ICMP = 1,
+        TCP = 6,
+        UDP = 17,
+    )
+
+ipv4_header = Struct("ip_header",
+    EmbeddedBitStruct(
+        Const(Nibble("version"), 4),
+        ExprAdapter(Nibble("header_length"), 
+            decoder = lambda obj, ctx: obj * 4, 
+            encoder = lambda obj, ctx: obj / 4
+        ),
+    ),
+    BitStruct("tos",
+        Bits("precedence", 3),
+        Flag("minimize_delay"),
+        Flag("high_throuput"),
+        Flag("high_reliability"),
+        Flag("minimize_cost"),
+        Padding(1),
+    ),
+    UBInt16("total_length"),
+    Value("payload_length", lambda ctx: ctx.total_length - ctx.header_length),
+    UBInt16("identification"),
+    EmbeddedBitStruct(
+        Struct("flags",
+            Padding(1),
+            Flag("dont_fragment"),
+            Flag("more_fragments"),
+        ),
+        Bits("frame_offset", 13),
+    ),
+    UBInt8("ttl"),
+    ProtocolEnum(UBInt8("protocol")),
+    UBInt16("checksum"),
+    IpAddress("source"),
+    IpAddress("destination"),
+    Field("options", lambda ctx: ctx.header_length - 20),
+)
+
+
+if __name__ == "__main__":
+    cap = unhexlify(six.b("4500003ca0e3000080116185c0a80205d474a126"))
+    obj = ipv4_header.parse(cap)
+    print (obj)
+    print (repr(ipv4_header.build(obj)))
+
+
+
+
+
+
+
+
+