initial commit

.classpath

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+<?xml version="1.0" encoding="UTF-8"?>
+<classpath>
+	<classpathentry kind="src" output="target/classes" path="src/main/java">
+		<attributes>
+			<attribute name="optional" value="true"/>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry excluding="**" kind="src" output="target/classes" path="src/main/resources">
+		<attributes>
+			<attribute name="maven.pomderived" value="true"/>
+			<attribute name="optional" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="src" output="target/test-classes" path="src/test/java">
+		<attributes>
+			<attribute name="test" value="true"/>
+			<attribute name="optional" value="true"/>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry excluding="**" kind="src" output="target/test-classes" path="src/test/resources">
+		<attributes>
+			<attribute name="test" value="true"/>
+			<attribute name="maven.pomderived" value="true"/>
+			<attribute name="optional" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-17">
+		<attributes>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">
+		<attributes>
+			<attribute name="maven.pomderived" value="true"/>
+		</attributes>
+	</classpathentry>
+	<classpathentry kind="output" path="target/classes"/>
+</classpath>

.gitignore

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+/target/
+/.settings/

.project

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+<?xml version="1.0" encoding="UTF-8"?>
+<projectDescription>
+	<name>netsim</name>
+	<comment></comment>
+	<projects>
+	</projects>
+	<buildSpec>
+		<buildCommand>
+			<name>org.eclipse.jdt.core.javabuilder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+		<buildCommand>
+			<name>org.eclipse.m2e.core.maven2Builder</name>
+			<arguments>
+			</arguments>
+		</buildCommand>
+	</buildSpec>
+	<natures>
+		<nature>org.eclipse.jdt.core.javanature</nature>
+		<nature>org.eclipse.m2e.core.maven2Nature</nature>
+	</natures>
+</projectDescription>

pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" >
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>eu.m724</groupId>
+  <artifactId>netsim</artifactId>
+  <version>0.0.1-SNAPSHOT</version>
+  
+  <properties>
+    <maven.compiler.target>17</maven.compiler.target>
+    <maven.compiler.source>17</maven.compiler.source>
+  </properties>
+  
+  <dependencies>
+	<dependency>
+	  <groupId>junit</groupId>
+	  <artifactId>junit</artifactId>
+	  <version>4.13.2</version>
+	  <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

src/main/java/eu/m724/netsim/Machine.java

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+package eu.m724.netsim;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+
+public class Machine {
+	public final String id;
+	
+	private List<Machine> peers = new ArrayList<>();
+	// key - destination
+	private HashMap<Machine, RoutingInfo> routingTable = new HashMap<>();
+	
+	
+	public Machine(String id) {
+		this.id = id;
+	}
+	
+	
+	/**
+	 * get route to machine
+	 * @param machine the machine to get route to
+	 * @return the route to machine
+	 */
+	public RoutingInfo getRouteTo(Machine machine) {
+		return routingTable.get(machine);
+	}
+	
+	/**
+	 * import a route
+	 * @param from the machine the route is imported from
+	 * @param route
+	 * @return if I accepted the route
+	 */
+	public boolean importRoute(Machine from, RoutingInfo route) {
+		Machine dest = route.dest();
+		int pathLength = route.pathLength();
+		
+		// if this route leads to this machine
+		//                       or via this machine          or the route is from an unknown machine
+		if (dest.equals(this) || route.from().equals(this) || !route.from().equals(from)) {
+			System.out.printf("%s rejected from %s route %s\n", id, from.id, route.toString());
+			return false;
+		}
+		
+		RoutingInfo existingInfo = routingTable.get(dest);
+		
+		// reject if destination already exists and is faster
+		if (existingInfo != null && existingInfo.pathLength() < pathLength) {
+			return false;
+		}
+		
+		// TODO other import filtering here
+		
+		routingTable.put(route.dest(), route);
+		
+		if (from.equals(dest) && pathLength == 1)
+			System.out.printf("%s accepted direct from %s\n", id, from.id);
+		else
+			System.out.printf("%s accepted from %s route %s\n", id, from.id, route.toString());
+		
+		for (Machine peer : peers) {
+			if (peer.equals(from) || peer.equals(dest)) continue;
+			exportRoute(peer, route);
+		}
+		
+		return true;
+	}
+	
+	/**
+	 * export a route
+	 * @param to the machine to export a route to
+	 * @param route
+	 * @return if the machine accepted the route
+	 */
+	public boolean exportRoute(Machine to, RoutingInfo route) {
+		if (route == null) return false;
+		if (to.equals(route.dest())) return false;
+		if (to.equals(route.from())) return false;
+		// TODO export filtering here
+		System.out.printf("%s exports to %s route %s\n", id, to.id, route.toString());
+		return to.importRoute(this, route.nextHop(this));
+	}
+	
+	/**
+	 * 
+	 * @param to the machine to export a route to
+	 * @param dest the destination of exported route
+	 * @return if the machine accepted the route
+	 */
+	public boolean exportRouteTo(Machine to, Machine dest) {
+		return exportRoute(to, routingTable.get(dest));
+	}
+	
+	
+	/**
+	 * peer with somebody
+	 * all tables are exported
+	 * @param machine the machine to peer with
+	 * @return peering successful (if not already peering)
+	 */
+	public boolean peer(Machine machine) {
+		System.out.printf("%s peering with %s\n", id, machine.id);
+		boolean success = peers.add(machine);
+		importRoute(machine, RoutingInfo.direct(machine));
+		for (RoutingInfo route : routingTable.values()) {
+			exportRoute(machine, route);
+		}
+		return success;
+	}
+
+	/**
+	 * peer with somebody and make that somebody peer with me
+	 * all tables are exported
+	 * @param machine the machine to peer with
+	 * @return peering successful (if not already peering)
+	 */
+	public boolean peerWith(Machine machine) {
+		if (peer(machine)) return machine.peer(this);
+		return false;
+	}
+	
+	
+	@Override
+	public boolean equals(Object object) {
+		if (object == this) return true;
+		if (object == null) return false;
+		if (!(object instanceof Machine)) return false;
+		Machine machine = (Machine) object;
+		if (!machine.id.equals(this.id)) return false;
+		
+		return true;
+	}
+}

src/main/java/eu/m724/netsim/RoutingInfo.java

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+package eu.m724.netsim;
+
+public record RoutingInfo(Machine dest, Machine from, int pathLength) {
+	public String toString() {
+		return "%s via %s len %d".formatted(dest.id, from.id, pathLength);
+	}
+	
+	public RoutingInfo nextHop(Machine from) {
+		return new RoutingInfo(dest, from, pathLength + 1);
+	}
+	
+	public static RoutingInfo direct(Machine machine) {
+		return new RoutingInfo(machine, machine, 1);
+	}
+}

src/test/java/netsim/PeeringTest.java

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+package netsim;
+
+import org.junit.Test;
+
+import eu.m724.netsim.Machine;
+
+public class PeeringTest {
+	@Test
+	public void testPeering() {
+		// machine1 - machine2 - machine3
+		// so machine1 goes to machine3 through machine2
+		
+		Machine machine1 = new Machine("machine1");
+		Machine machine2 = new Machine("machine2");
+		Machine machine3 = new Machine("machine3");
+
+		machine1.peerWith(machine2);
+		machine2.peerWith(machine3);
+		
+		System.out.println("");
+		System.out.println(machine1.getRouteTo(machine2).toString());
+		System.out.println(machine2.getRouteTo(machine3).toString());
+		System.out.println(machine1.getRouteTo(machine3).toString());
+	}
+}