1 files changed, 61 insertions, 0 deletions
diff --git a/external/construct/protocols/layer4/tcp.py b/external/construct/protocols/layer4/tcp.py
new file mode 100644
index 0000000..44f1bd7
--- /dev/null
+++ b/external/construct/protocols/layer4/tcp.py
@@ -0,0 +1,61 @@
+"""
+Transmission Control Protocol (TCP/IP protocol stack)
+"""
+from construct import *
+from binascii import unhexlify
+import six
+
+
+tcp_header = Struct("tcp_header",
+    UBInt16("source"),
+    UBInt16("destination"),
+    UBInt32("seq"),
+    UBInt32("ack"),
+    EmbeddedBitStruct(
+        ExprAdapter(Nibble("header_length"), 
+            encoder = lambda obj, ctx: obj / 4,
+            decoder = lambda obj, ctx: obj * 4,
+        ),
+        Padding(3),
+        Struct("flags",
+            Flag("ns"),
+            Flag("cwr"),
+            Flag("ece"),
+            Flag("urg"),
+            Flag("ack"),
+            Flag("psh"),
+            Flag("rst"),
+            Flag("syn"),
+            Flag("fin"),
+        ),
+    ),
+    UBInt16("window"),
+    UBInt16("checksum"),
+    UBInt16("urgent"),
+    Field("options", lambda ctx: ctx.header_length - 20),
+)
+
+if __name__ == "__main__":
+    cap = unhexlify(six.b("0db5005062303fb21836e9e650184470c9bc0000"))
+    
+    obj = tcp_header.parse(cap)
+    print (obj)
+    built = tcp_header.build(obj)
+    print (built)
+    assert cap == built
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+