Add new logical level - IpPayload

IpPacket consists of IpHeader and IpPayload.
IpHeader can be IPv4 or IPv6.
IpPayload can be TCP, UDP, ICMP, etc.

Earlier we inherited each IP Packet type directly from IpPacket.

Author: hirsivaja

src/main/java/com/github/hirsivaja/ip/IpPacket.java

@@ -14,6 +14,7 @@
 public sealed interface IpPacket extends EthernetPayload permits Ipv4Packet, Ipv6Packet {
     Logger logger = Logger.getLogger("IpPacket");
     IpHeader header();
+    IpPayload payload();
 
     @Override
     default byte[] toBytes() {

src/main/java/com/github/hirsivaja/ip/IpPayload.java

@@ -0,0 +1,11 @@
+package com.github.hirsivaja.ip;
+
+import com.github.hirsivaja.ip.ipv4.Ipv4Payload;
+import com.github.hirsivaja.ip.ipv6.Ipv6Payload;
+
+import java.nio.ByteBuffer;
+
+public sealed interface IpPayload permits Ipv4Payload, Ipv6Payload {
+    void encode(ByteBuffer out);
+    int length();
+}

src/main/java/com/github/hirsivaja/ip/icmp/AddressMaskReply.java

@@ -13,7 +13,7 @@ public void encode(ByteBuffer out) {
 
     @Override
     public int length() {
-        return BASE_LEN + 8;
+        return 8;
     }
 
     public static IcmpMessage decode(ByteBuffer in) {

src/main/java/com/github/hirsivaja/ip/icmp/AddressMaskRequest.java

@@ -13,7 +13,7 @@ public void encode(ByteBuffer out) {
 
     @Override
     public int length() {
-        return BASE_LEN + 8;
+        return 8;
     }
 
     public static IcmpMessage decode(ByteBuffer in) {

src/main/java/com/github/hirsivaja/ip/icmp/DestinationUnreachable.java

@@ -16,7 +16,7 @@ public void encode(ByteBuffer out) {
 
     @Override
     public int length() {
-        return BASE_LEN + 4 + payload.array().length;
+        return 4 + payload.array().length;
     }
 
     public static IcmpMessage decode(ByteBuffer in, IcmpCode code) {

src/main/java/com/github/hirsivaja/ip/icmp/EchoReply.java

@@ -17,7 +17,7 @@ public void encode(ByteBuffer out) {
 
     @Override
     public int length() {
-        return BASE_LEN + 4 + payload.array().length;
+        return 4 + payload.array().length;
     }
 
     public static IcmpMessage decode(ByteBuffer in) {

src/main/java/com/github/hirsivaja/ip/icmp/EchoRequest.java

@@ -18,7 +18,7 @@ public void encode(ByteBuffer out) {
 
     @Override
     public int length() {
-        return BASE_LEN + 4 + payload.array().length;
+        return 4 + payload.array().length;
     }
 
     public static IcmpMessage decode(ByteBuffer in) {

src/main/java/com/github/hirsivaja/ip/icmp/ExtendedEchoReply.java

@@ -31,7 +31,7 @@ public void encode(ByteBuffer out) {
 
     @Override
     public int length() {
-        return BASE_LEN + 4;
+        return 4;
     }
 
     public static IcmpMessage decode(ByteBuffer in, IcmpCode code) {

src/main/java/com/github/hirsivaja/ip/icmp/ExtendedEchoRequest.java

@@ -24,7 +24,7 @@ public void encode(ByteBuffer out) {
 
     @Override
     public int length() {
-        return BASE_LEN + 4 + extension.array().length;
+        return 4 + extension.array().length;
     }
 
     public static IcmpMessage decode(ByteBuffer in) {

src/main/java/com/github/hirsivaja/ip/icmp/GenericIcmpMessage.java

@@ -16,7 +16,7 @@ public void encode(ByteBuffer out) {
 
     @Override
     public int length() {
-        return BASE_LEN + payload.array().length;
+        return payload.array().length;
     }
 
     public static IcmpMessage decode(ByteBuffer in, IcmpType type, IcmpCode code) {