Added documentation, flags, TCP options skipping (see #353)

network/tcp_segment.ksy

@@ -5,9 +5,11 @@ meta:
     rfc:
       - 793
       - 1323
+      - 9293
     wikidata: Q8803
   license: CC0-1.0
   endian: be
+  ks-version: 0.10
 doc: |
   TCP is one of the core Internet protocols on transport layer (AKA
   OSI layer 4), providing stateful connections with error checking,
@@ -16,21 +18,69 @@ doc: |
 seq:
   - id: src_port
     type: u2
+    doc: Source port
   - id: dst_port
     type: u2
+    doc: Destination port
   - id: seq_num
     type: u4
+    doc: Sequence number
   - id: ack_num
     type: u4
-  - id: b12
-    type: u1
-  - id: b13
-    type: u1
+    doc: Acknowledgment number
+  - id: data_offset
+    type: b4
+    doc: Data offset (in 32-bit words from the beginning of this type, normally 32 or can be extended if there are any TCP options or padding is present)
+  - id: reserved
+    type: b4
+  - id: flags
+    type: flags
   - id: window_size
     type: u2
   - id: checksum
     type: u2
   - id: urgent_pointer
     type: u2
+  - id: options
+    size: (data_offset * 4) - 20
+    if: ((data_offset * 4) - 20) != 0
   - id: body
     size-eos: true
+types:
+  flags:
+    doc: |
+      TCP header flags as defined "TCP Header Flags" registry.
+    seq:
+      - id: cwr
+        type: b1
+        doc: Congestion Window Reduced
+      - id: ece
+        type: b1
+        doc: ECN-Echo
+      - id: urg
+        type: b1
+        doc: Urgent pointer field is significant
+      - id: ack
+        type: b1
+        doc: Acknowledgment field is significant
+      - id: psh
+        type: b1
+        doc: Push function
+      - id: rst
+        type: b1
+        doc: Reset the connection
+      - id: syn
+        type: b1
+        doc: Synchronize sequence numbers
+      - id: fin
+        type: b1
+        doc: No more data from sender
+    to-string: |
+      (cwr ? "|CWR" : "") +
+      (ece ? "|ECE" : "") +
+      (urg ? "|URG" : "") +
+      (ack ? "|ACK" : "") +
+      (psh ? "|PSH" : "") +
+      (rst ? "|RST" : "") +
+      (syn ? "|SYN" : "") +
+      (fin ? "|FIN" : "")