Show which contacts subscribe to each forum. Dev task #79.

briar-core/src/org/briarproject/db/Database.java

@@ -486,6 +486,13 @@ interface Database<T> {
 	 */
 	Settings getSettings(T txn) throws DbException;
 
+	/**
+	 * Returns all contacts who subscribe to the given group.
+	 * <p>
+	 * Locking: subscription read.
+	 */
+	Collection<Contact> getSubscribers(T txn, GroupId g) throws DbException;
+
 	/**
 	 * Returns a subscription ack for the given contact, or null if no ack is
 	 * due.

briar-core/src/org/briarproject/db/DatabaseComponentImpl.java

@@ -1154,6 +1154,23 @@ DatabaseCleaner.Callback {
 		}
 	}
 
+	public Collection<Contact> getSubscribers(GroupId g) throws DbException {
+		subscriptionLock.readLock().lock();
+		try {
+			T txn = db.startTransaction();
+			try {
+				Collection<Contact> contacts = db.getSubscribers(txn, g);
+				db.commitTransaction(txn);
+				return contacts;
+			} catch(DbException e) {
+				db.abortTransaction(txn);
+				throw e;
+			}
+		} finally {
+			subscriptionLock.readLock().unlock();
+		}
+	}
+
 	public Map<TransportId, Long> getTransportLatencies() throws DbException {
 		transportLock.readLock().lock();
 		try {

briar-core/src/org/briarproject/db/JdbcDatabase.java

@@ -2154,6 +2154,40 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	public Collection<Contact> getSubscribers(Connection txn, GroupId g)
+			throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT c.contactId, authorId, c.name, publicKey,"
+					+ " localAuthorId"
+					+ " FROM contacts AS c"
+					+ " JOIN contactGroups AS cg"
+					+ " ON c.contactId = cg.contactId"
+					+ " WHERE groupId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setBytes(1, g.getBytes());
+			rs = ps.executeQuery();
+			List<Contact> contacts = new ArrayList<Contact>();
+			while(rs.next()) {
+				ContactId contactId = new ContactId(rs.getInt(1));
+				AuthorId authorId = new AuthorId(rs.getBytes(2));
+				String name = rs.getString(3);
+				byte[] publicKey = rs.getBytes(4);
+				Author author = new Author(authorId, name, publicKey);
+				AuthorId localAuthorId = new AuthorId(rs.getBytes(5));
+				contacts.add(new Contact(contactId, author, localAuthorId));
+			}
+			rs.close();
+			ps.close();
+			return Collections.unmodifiableList(contacts);
+		} catch(SQLException e) {
+			tryToClose(rs);
+			tryToClose(ps);
+			throw new DbException(e);
+		}
+	}
+
 	public SubscriptionAck getSubscriptionAck(Connection txn, ContactId c)
 			throws DbException {
 		PreparedStatement ps = null;