Add an IntroductionManager and Validator

This Introduction BSP Client uses its own group to communicate with
existing contacts. It uses four types of messages to facilitate
introductions: the introduction, the response, the ack and the abort.

The protocol logic is encapsulated in two protocol engines, one for the
introducer and one for the introducee. The introduction client keeps the
local state for each engine, hands messages over to the engines and
processes the result and state changes they return.

briar-api/src/org/briarproject/api/introduction/IntroducerAction.java

@@ -0,0 +1,46 @@
+package org.briarproject.api.introduction;
+
+import static org.briarproject.api.introduction.IntroductionConstants.TYPE_ABORT;
+import static org.briarproject.api.introduction.IntroductionConstants.TYPE_ACK;
+import static org.briarproject.api.introduction.IntroductionConstants.TYPE_REQUEST;
+import static org.briarproject.api.introduction.IntroductionConstants.TYPE_RESPONSE;
+
+public enum IntroducerAction {
+
+	LOCAL_REQUEST,
+	LOCAL_ABORT,
+	REMOTE_ACCEPT_1,
+	REMOTE_ACCEPT_2,
+	REMOTE_DECLINE_1,
+	REMOTE_DECLINE_2,
+	REMOTE_ABORT,
+	ACK_1,
+	ACK_2;
+
+	public static IntroducerAction getLocal(int type) {
+		if (type == TYPE_REQUEST) return LOCAL_REQUEST;
+		if (type == TYPE_ABORT) return LOCAL_ABORT;
+		return null;
+	}
+
+	public static IntroducerAction getRemote(int type, boolean one,
+			boolean accept) {
+
+		if (one) {
+			if (type == TYPE_RESPONSE && accept) return REMOTE_ACCEPT_1;
+			if (type == TYPE_RESPONSE) return REMOTE_DECLINE_1;
+			if (type == TYPE_ACK) return ACK_1;
+		} else {
+			if (type == TYPE_RESPONSE && accept) return REMOTE_ACCEPT_2;
+			if (type == TYPE_RESPONSE) return REMOTE_DECLINE_2;
+			if (type == TYPE_ACK) return ACK_2;
+		}
+		if (type == TYPE_ABORT) return REMOTE_ABORT;
+		return null;
+	}
+
+	public static IntroducerAction getRemote(int type, boolean one) {
+		return getRemote(type, one, true);
+	}
+
+}