Limit the number of subscriptions per user.

This limit is necessary to limit the size of subscription update
packets; it can be lifted when incremental subscription updates are
implemented.

briar-core/src/net/sf/briar/db/Database.java

@@ -132,11 +132,12 @@ interface Database<T> {
 			throws DbException;
 
 	/**
-	 * Subscribes to the given group.
+	 * Subscribes to the given group, or returns false if the user already has
+	 * the maximum number of subscriptions.
 	 * <p>
 	 * Locking: subscription write.
 	 */
-	void addSubscription(T txn, Group g) throws DbException;
+	boolean addSubscription(T txn, Group g) throws DbException;
 
 	/**
 	 * Adds a new transport to the database.

briar-core/src/net/sf/briar/db/DatabaseComponentImpl.java

@@ -1715,14 +1715,16 @@ DatabaseCleaner.Callback {
 			callListeners(new LocalSubscriptionsUpdatedEvent(affected));
 	}
 
-	public void subscribe(Group g) throws DbException {
+	public boolean subscribe(Group g) throws DbException {
 		subscriptionLock.writeLock().lock();
 		try {
 			T txn = db.startTransaction();
 			try {
+				boolean added = false;
 				if(!db.containsSubscription(txn, g.getId()))
-					db.addSubscription(txn, g);
+					added = db.addSubscription(txn, g);
 				db.commitTransaction(txn);
+				return added;
 			} catch(DbException e) {
 				db.abortTransaction(txn);
 				throw e;

briar-core/src/net/sf/briar/db/JdbcDatabase.java

@@ -4,6 +4,7 @@ import static java.sql.Types.BINARY;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 import static net.sf.briar.api.Rating.UNRATED;
+import static net.sf.briar.api.messaging.MessagingConstants.MAX_SUBSCRIPTIONS;
 import static net.sf.briar.db.DatabaseConstants.RETENTION_MODULUS;
 import static net.sf.briar.db.ExponentialBackoff.calculateExpiry;
 
@@ -709,11 +710,21 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
-	public void addSubscription(Connection txn, Group g) throws DbException {
+	public boolean addSubscription(Connection txn, Group g) throws DbException {
 		PreparedStatement ps = null;
+		ResultSet rs = null;
 		try {
-			String sql = "INSERT INTO groups"
-					+ " (groupId, name, key) VALUES (?, ?, ?)";
+			String sql = "SELECT COUNT (groupId) from GROUPS";
+			ps = txn.prepareStatement(sql);
+			rs = ps.executeQuery();
+			if(!rs.next()) throw new DbStateException();
+			int count = rs.getInt(1);
+			if(rs.next()) throw new DbStateException();
+			rs.close();
+			ps.close();
+			if(count > MAX_SUBSCRIPTIONS) throw new DbStateException();
+			if(count == MAX_SUBSCRIPTIONS) return false;
+			sql = "INSERT INTO groups (groupId, name, key) VALUES (?, ?, ?)";
 			ps = txn.prepareStatement(sql);
 			ps.setBytes(1, g.getId().getBytes());
 			ps.setString(2, g.getName());
@@ -721,6 +732,7 @@ abstract class JdbcDatabase implements Database<Connection> {
 			int affected = ps.executeUpdate();
 			if(affected != 1) throw new DbStateException();
 			ps.close();
+			return true;
 		} catch(SQLException e) {
 			tryToClose(ps);
 			throw new DbException(e);

briar-core/src/net/sf/briar/messaging/PacketReaderImpl.java

@@ -221,8 +221,7 @@ class PacketReaderImpl implements PacketReader {
 		r.setMaxStringLength(MAX_PROPERTY_LENGTH);
 		Map<String, String> m = r.readMap(String.class, String.class);
 		r.resetMaxStringLength();
-		if(m.size() > MAX_PROPERTIES_PER_TRANSPORT)
-			throw new FormatException();
+		if(m.size() > MAX_PROPERTIES_PER_TRANSPORT) throw new FormatException();
 		// Read the version number
 		long version = r.readInt64();
 		if(version < 0) throw new FormatException();

briar-core/src/net/sf/briar/messaging/SubscriptionUpdateReader.java

@@ -1,6 +1,7 @@
 package net.sf.briar.messaging;
 
 import static net.sf.briar.api.messaging.MessagingConstants.MAX_PACKET_LENGTH;
+import static net.sf.briar.api.messaging.MessagingConstants.MAX_SUBSCRIPTIONS;
 import static net.sf.briar.api.messaging.Types.SUBSCRIPTION_UPDATE;
 
 import java.io.IOException;
@@ -31,7 +32,8 @@ class SubscriptionUpdateReader implements StructReader<SubscriptionUpdate> {
 		// Read the subscriptions
 		List<Group> subs = new ArrayList<Group>();
 		r.readListStart();
-		while(!r.hasListEnd()) subs.add(groupReader.readStruct(r));
+		for(int i = 0; i < MAX_SUBSCRIPTIONS && !r.hasListEnd(); i++)
+			subs.add(groupReader.readStruct(r));
 		r.readListEnd();
 		// Read the version number
 		long version = r.readInt64();