Re-introduce InvitationResponse

This was done, so private responses don't need to include a Nameable already.
Retreiving a nameable is tricky and requires a data migration,
so we just don't do it now.

briar-android/src/main/java/org/briarproject/briar/android/blog/BlogControllerImpl.java

@@ -21,11 +21,11 @@ import org.briarproject.briar.android.controller.ActivityLifecycleController;
 import org.briarproject.briar.android.controller.handler.ResultExceptionHandler;
 import org.briarproject.briar.api.android.AndroidNotificationManager;
 import org.briarproject.briar.api.blog.Blog;
+import org.briarproject.briar.api.blog.BlogInvitationResponse;
 import org.briarproject.briar.api.blog.BlogManager;
 import org.briarproject.briar.api.blog.BlogSharingManager;
 import org.briarproject.briar.api.blog.event.BlogInvitationResponseReceivedEvent;
 import org.briarproject.briar.api.blog.event.BlogPostAddedEvent;
-import org.briarproject.briar.api.messaging.PrivateResponse;
 import org.briarproject.briar.api.sharing.event.ContactLeftShareableEvent;
 
 import java.util.ArrayList;
@@ -107,8 +107,8 @@ class BlogControllerImpl extends BaseControllerImpl
 		} else if (e instanceof BlogInvitationResponseReceivedEvent) {
 			BlogInvitationResponseReceivedEvent b =
 					(BlogInvitationResponseReceivedEvent) e;
-			PrivateResponse<Blog> r = b.getMessageHeader();
-			if (r.getNameable().getId().equals(groupId) && r.wasAccepted()) {
+			BlogInvitationResponse r = b.getMessageHeader();
+			if (r.getShareableId().equals(groupId) && r.wasAccepted()) {
 				LOG.info("Blog invitation accepted");
 				onBlogInvitationAccepted(b.getContactId());
 			}

briar-android/src/main/java/org/briarproject/briar/android/contact/ConversationItem.java

@@ -167,14 +167,14 @@ abstract class ConversationItem {
 			if (ir.wasAccepted()) {
 				text = ctx.getString(
 						R.string.introduction_response_accepted_sent,
-						ir.getNameable().getName());
+						ir.getIntroducedAuthor().getName());
 				text += "\n\n" + ctx.getString(
 						R.string.introduction_response_accepted_sent_info,
-						ir.getNameable().getName());
+						ir.getIntroducedAuthor().getName());
 			} else {
 				text = ctx.getString(
 						R.string.introduction_response_declined_sent,
-						ir.getNameable().getName());
+						ir.getIntroducedAuthor().getName());
 			}
 			return new ConversationNoticeOutItem(ir.getId(), ir.getGroupId(),
 					text, null, ir.getTimestamp(), ir.isSent(), ir.isSeen());
@@ -191,7 +191,7 @@ abstract class ConversationItem {
 				}
 			}
 			String text =
-					ctx.getString(res, contactName, ir.getNameable().getName());
+					ctx.getString(res, contactName, ir.getIntroducedAuthor().getName());
 			return new ConversationNoticeInItem(ir.getId(), ir.getGroupId(),
 					text, null, ir.getTimestamp(), ir.isRead());
 		}

briar-android/src/main/java/org/briarproject/briar/android/forum/ForumControllerImpl.java

@@ -85,7 +85,7 @@ class ForumControllerImpl extends
 			ForumInvitationResponseReceivedEvent f =
 					(ForumInvitationResponseReceivedEvent) e;
 			ForumInvitationResponse r = f.getMessageHeader();
-			if (r.getNameable().getId().equals(getGroupId()) && r.wasAccepted()) {
+			if (r.getShareableId().equals(getGroupId()) && r.wasAccepted()) {
 				LOG.info("Forum invitation was accepted");
 				onForumInvitationAccepted(f.getContactId());
 			}

briar-android/src/main/java/org/briarproject/briar/android/privategroup/conversation/GroupControllerImpl.java

@@ -100,7 +100,7 @@ class GroupControllerImpl extends
 			GroupInvitationResponseReceivedEvent g =
 					(GroupInvitationResponseReceivedEvent) e;
 			GroupInvitationResponse r = g.getMessageHeader();
-			if (getGroupId().equals(r.getNameable().getId()) && r.wasAccepted()) {
+			if (getGroupId().equals(r.getShareableId()) && r.wasAccepted()) {
 				listener.runOnUiThreadUnlessDestroyed(
 						() -> listener.onInvitationAccepted(g.getContactId()));
 			}

briar-api/src/main/java/org/briarproject/briar/api/blog/BlogInvitationResponse.java

@@ -4,16 +4,16 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.briar.api.client.SessionId;
-import org.briarproject.briar.api.messaging.PrivateResponse;
+import org.briarproject.briar.api.sharing.InvitationResponse;
 
 @NotNullByDefault
-public class BlogInvitationResponse extends PrivateResponse<Blog> {
+public class BlogInvitationResponse extends InvitationResponse {
 
 	public BlogInvitationResponse(MessageId id, GroupId groupId, long time,
 			boolean local, boolean sent, boolean seen, boolean read,
-			SessionId sessionId, Blog blog, boolean accept) {
-		super(id, groupId, time, local, sent, seen, read, sessionId, blog,
-				accept);
+			SessionId sessionId, boolean accept, GroupId shareableId) {
+		super(id, groupId, time, local, sent, seen, read, sessionId,
+				accept, shareableId);
 	}
 
 }

briar-api/src/main/java/org/briarproject/briar/api/forum/ForumInvitationResponse.java

@@ -4,19 +4,19 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.briar.api.client.SessionId;
-import org.briarproject.briar.api.messaging.PrivateResponse;
+import org.briarproject.briar.api.sharing.InvitationResponse;
 
 import javax.annotation.concurrent.Immutable;
 
 @Immutable
 @NotNullByDefault
-public class ForumInvitationResponse extends PrivateResponse<Forum> {
+public class ForumInvitationResponse extends InvitationResponse {
 
 	public ForumInvitationResponse(MessageId id, GroupId groupId, long time,
 			boolean local, boolean sent, boolean seen, boolean read,
-			SessionId sessionId, Forum forum, boolean accept) {
-		super(id, groupId, time, local, sent, seen, read, sessionId, forum,
-				accept);
+			SessionId sessionId, boolean accept, GroupId shareableId) {
+		super(id, groupId, time, local, sent, seen, read, sessionId,
+				accept, shareableId);
 	}
 
 }

briar-api/src/main/java/org/briarproject/briar/api/introduction/IntroductionResponse.java

@@ -13,18 +13,24 @@ import static org.briarproject.briar.api.introduction.Role.INTRODUCER;
 
 @Immutable
 @NotNullByDefault
-public class IntroductionResponse extends PrivateResponse<Author> {
+public class IntroductionResponse extends PrivateResponse {
 
+	private final Author introducedAuthor;
 	private final Role ourRole;
 
 	public IntroductionResponse(MessageId messageId, GroupId groupId, long time,
 			boolean local, boolean sent, boolean seen, boolean read,
-			SessionId sessionId, Author author, boolean accepted, Role role) {
+			SessionId sessionId, boolean accepted, Author author, Role role) {
 		super(messageId, groupId, time, local, sent, seen, read, sessionId,
-				author, accepted);
+				accepted);
+		this.introducedAuthor = author;
 		this.ourRole = role;
 	}
 
+	public Author getIntroducedAuthor() {
+		return introducedAuthor;
+	}
+
 	public boolean isIntroducer() {
 		return ourRole == INTRODUCER;
 	}

briar-api/src/main/java/org/briarproject/briar/api/messaging/PrivateResponse.java

 package org.briarproject.briar.api.messaging;
 
-import org.briarproject.bramble.api.Nameable;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.MessageId;
@@ -10,19 +9,16 @@ import javax.annotation.concurrent.Immutable;
 
 @Immutable
 @NotNullByDefault
-public abstract class PrivateResponse<N extends Nameable>
-		extends PrivateMessageHeader {
+public abstract class PrivateResponse extends PrivateMessageHeader {
 
 	private final SessionId sessionId;
-	private final N nameable;
 	private final boolean accepted;
 
 	public PrivateResponse(MessageId id, GroupId groupId, long time,
 			boolean local, boolean sent, boolean seen, boolean read,
-			SessionId sessionId, N nameable, boolean accepted) {
+			SessionId sessionId, boolean accepted) {
 		super(id, groupId, time, local, sent, seen, read);
 		this.sessionId = sessionId;
-		this.nameable = nameable;
 		this.accepted = accepted;
 	}
 
@@ -30,10 +26,6 @@ public abstract class PrivateResponse<N extends Nameable>
 		return sessionId;
 	}
 
-	public N getNameable() {
-		return nameable;
-	}
-
 	public boolean wasAccepted() {
 		return accepted;
 	}

briar-api/src/main/java/org/briarproject/briar/api/privategroup/invitation/GroupInvitationResponse.java

@@ -4,20 +4,19 @@ import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.briar.api.client.SessionId;
-import org.briarproject.briar.api.messaging.PrivateResponse;
-import org.briarproject.briar.api.privategroup.PrivateGroup;
+import org.briarproject.briar.api.sharing.InvitationResponse;
 
 import javax.annotation.concurrent.Immutable;
 
 @Immutable
 @NotNullByDefault
-public class GroupInvitationResponse extends PrivateResponse<PrivateGroup> {
+public class GroupInvitationResponse extends InvitationResponse {
 
 	public GroupInvitationResponse(MessageId id, GroupId groupId, long time,
 			boolean local, boolean sent, boolean seen, boolean read,
-			SessionId sessionId, PrivateGroup privateGroup, boolean accept) {
+			SessionId sessionId, boolean accept, GroupId shareableId) {
 		super(id, groupId, time, local, sent, seen, read, sessionId,
-				privateGroup, accept);
+				accept, shareableId);
 	}
 
 }

briar-api/src/main/java/org/briarproject/briar/api/sharing/InvitationResponse.java

+package org.briarproject.briar.api.sharing;
+
+import org.briarproject.bramble.api.sync.GroupId;
+import org.briarproject.bramble.api.sync.MessageId;
+import org.briarproject.briar.api.client.SessionId;
+import org.briarproject.briar.api.messaging.PrivateResponse;
+
+public abstract class InvitationResponse extends PrivateResponse {
+
+	private final GroupId shareableId;
+
+	public InvitationResponse(MessageId id, GroupId groupId, long time,
+			boolean local, boolean sent, boolean seen, boolean read,
+			SessionId sessionId, boolean accepted, GroupId shareableId) {
+		super(id, groupId, time, local, sent, seen, read, sessionId, accepted);
+		this.shareableId = shareableId;
+	}
+
+	public GroupId getShareableId() {
+		return shareableId;
+	}
+
+}

briar-core/src/main/java/org/briarproject/briar/introduction/AbstractProtocolEngine.java

@@ -152,8 +152,8 @@ abstract class AbstractProtocolEngine<S extends Session>
 		IntroductionResponse response =
 				new IntroductionResponse(m.getMessageId(), m.getGroupId(),
 						m.getTimestamp(), false, false, false, false,
-						s.getSessionId(), otherAuthor,
-						m instanceof AcceptMessage, s.getRole());
+						s.getSessionId(), m instanceof AcceptMessage,
+						otherAuthor, s.getRole());
 		IntroductionResponseReceivedEvent e =
 				new IntroductionResponseReceivedEvent(response, c.getId());
 		txn.attach(e);

briar-core/src/main/java/org/briarproject/briar/introduction/IntroductionManagerImpl.java

@@ -495,7 +495,7 @@ class IntroductionManagerImpl extends ConversationClientImpl
 		} else throw new AssertionError();
 		return new IntroductionResponse(m, contactGroupId, meta.getTimestamp(),
 				meta.isLocal(), status.isSent(), status.isSeen(), meta.isRead(),
-				sessionId, author, accept, role);
+				sessionId, accept, author, role);
 	}
 
 	private void removeSessionWithIntroducer(Transaction txn,

briar-core/src/main/java/org/briarproject/briar/privategroup/invitation/CreatorProtocolEngine.java

@@ -15,7 +15,6 @@ import org.briarproject.briar.api.client.MessageTracker;
 import org.briarproject.briar.api.client.ProtocolStateException;
 import org.briarproject.briar.api.client.SessionId;
 import org.briarproject.briar.api.privategroup.GroupMessageFactory;
-import org.briarproject.briar.api.privategroup.PrivateGroup;
 import org.briarproject.briar.api.privategroup.PrivateGroupFactory;
 import org.briarproject.briar.api.privategroup.PrivateGroupManager;
 import org.briarproject.briar.api.privategroup.event.GroupInvitationResponseReceivedEvent;
@@ -193,10 +192,8 @@ class CreatorProtocolEngine extends AbstractProtocolEngine<CreatorSession> {
 		setPrivateGroupVisibility(txn, s, SHARED);
 		// Broadcast an event
 		ContactId contactId = getContactId(txn, m.getContactGroupId());
-		PrivateGroup privateGroup =
-				privateGroupManager.getPrivateGroup(txn, m.getPrivateGroupId());
 		txn.attach(new GroupInvitationResponseReceivedEvent(
-				createInvitationResponse(m, privateGroup, true), contactId));
+				createInvitationResponse(m, true), contactId));
 		// Move to the JOINED state
 		return new CreatorSession(s.getContactGroupId(), s.getPrivateGroupId(),
 				sent.getId(), m.getId(), sent.getTimestamp(),
@@ -217,10 +214,8 @@ class CreatorProtocolEngine extends AbstractProtocolEngine<CreatorSession> {
 				m.getTimestamp(), false);
 		// Broadcast an event
 		ContactId contactId = getContactId(txn, m.getContactGroupId());
-		PrivateGroup privateGroup =
-				privateGroupManager.getPrivateGroup(txn, m.getPrivateGroupId());
 		txn.attach(new GroupInvitationResponseReceivedEvent(
-				createInvitationResponse(m, privateGroup, false), contactId));
+				createInvitationResponse(m, false), contactId));
 		// Move to the START state
 		return new CreatorSession(s.getContactGroupId(), s.getPrivateGroupId(),
 				s.getLastLocalMessageId(), m.getId(), s.getLocalTimestamp(),
@@ -258,11 +253,10 @@ class CreatorProtocolEngine extends AbstractProtocolEngine<CreatorSession> {
 	}
 
 	private GroupInvitationResponse createInvitationResponse(
-			GroupInvitationMessage m, PrivateGroup privateGroup,
-			boolean accept) {
+			GroupInvitationMessage m, boolean accept) {
 		SessionId sessionId = new SessionId(m.getPrivateGroupId().getBytes());
 		return new GroupInvitationResponse(m.getId(), m.getContactGroupId(),
 				m.getTimestamp(), false, false, true, false, sessionId,
-				privateGroup, accept);
+				accept, m.getPrivateGroupId());
 	}
 }

briar-core/src/main/java/org/briarproject/briar/privategroup/invitation/GroupInvitationManagerImpl.java

@@ -378,36 +378,21 @@ class GroupInvitationManagerImpl extends ConversationClientImpl
 					.getMessageMetadataAsDictionary(txn, contactGroupId, query);
 			List<PrivateMessageHeader> messages =
 					new ArrayList<>(results.size());
-			// get invite message first and remember private groups
-			Map<SessionId, PrivateGroup> privateGroups = new HashMap<>();
 			for (Entry<MessageId, BdfDictionary> e : results.entrySet()) {
 				MessageId m = e.getKey();
 				MessageMetadata meta =
 						messageParser.parseMetadata(e.getValue());
-				MessageType type = meta.getMessageType();
-				if (type != INVITE) continue;
 				MessageStatus status = db.getMessageStatus(txn, c, m);
-				GroupInvitationRequest invite = parseInvitationRequest(txn,
-						contactGroupId, m, meta, status);
-				messages.add(invite);
-				privateGroups.put(invite.getSessionId(), invite.getNameable());
-			}
-			for (Entry<MessageId, BdfDictionary> e : results.entrySet()) {
-				MessageId m = e.getKey();
-				MessageMetadata meta =
-						messageParser.parseMetadata(e.getValue());
 				MessageType type = meta.getMessageType();
-				if (type == INVITE) continue;
-				MessageStatus status = db.getMessageStatus(txn, c, m);
-				SessionId sessionId = getSessionId(meta.getPrivateGroupId());
-				PrivateGroup privateGroup = privateGroups.get(sessionId);
-				if (privateGroup == null) throw new AssertionError();
-				if (type == JOIN) {
+				if (type == INVITE) {
+					messages.add(parseInvitationRequest(txn, contactGroupId, m,
+							meta, status));
+				} else if (type == JOIN) {
 					messages.add(parseInvitationResponse(contactGroupId, m,
-							meta, status, sessionId, privateGroup, true));
+							meta, status, true));
 				} else if (type == LEAVE) {
 					messages.add(parseInvitationResponse(contactGroupId, m,
-							meta, status, sessionId, privateGroup, false));
+							meta, status, false));
 				}
 			}
 			return messages;
@@ -436,12 +421,13 @@ class GroupInvitationManagerImpl extends ConversationClientImpl
 
 	private GroupInvitationResponse parseInvitationResponse(
 			GroupId contactGroupId, MessageId m, MessageMetadata meta,
-			MessageStatus status, SessionId sessionId,
-			PrivateGroup privateGroup, boolean accept) {
+			MessageStatus status, boolean accept) {
+		SessionId sessionId = getSessionId(meta.getPrivateGroupId());
 		return new GroupInvitationResponse(m, contactGroupId,
 				meta.getTimestamp(), meta.isLocal(), status.isSent(),
-				status.isSeen(), meta.isRead(), sessionId, privateGroup,
-				accept);
+				status.isSeen(), meta.isRead(), sessionId, accept,
+				meta.getPrivateGroupId()
+		);
 	}
 
 	@Override

briar-core/src/main/java/org/briarproject/briar/sharing/BlogInvitationFactoryImpl.java

@@ -30,10 +30,10 @@ public class BlogInvitationFactoryImpl
 	@Override
 	public BlogInvitationResponse createInvitationResponse(MessageId id,
 			GroupId contactGroupId, long time, boolean local, boolean sent,
-			boolean seen, boolean read, Blog blog, boolean accept) {
-		SessionId sessionId = new SessionId(blog.getId().getBytes());
+			boolean seen, boolean read, boolean accept, GroupId shareableId) {
+		SessionId sessionId = new SessionId(shareableId.getBytes());
 		return new BlogInvitationResponse(id, contactGroupId, time, local, sent,
-				seen, read, sessionId, blog, accept);
+				seen, read, sessionId, accept, shareableId);
 	}
 
 }

briar-core/src/main/java/org/briarproject/briar/sharing/BlogProtocolEngineImpl.java

@@ -58,21 +58,21 @@ class BlogProtocolEngineImpl extends ProtocolEngineImpl<Blog> {
 
 	@Override
 	Event getInvitationResponseReceivedEvent(AcceptMessage m,
-			ContactId contactId, Blog shareable) {
+			ContactId contactId) {
 		BlogInvitationResponse response = invitationFactory
 				.createInvitationResponse(m.getId(), m.getContactGroupId(),
 						m.getTimestamp(), false, false, true, false,
-						shareable, true);
+						true, m.getShareableId());
 		return new BlogInvitationResponseReceivedEvent(response, contactId);
 	}
 
 	@Override
 	Event getInvitationResponseReceivedEvent(DeclineMessage m,
-			ContactId contactId, Blog shareable) {
+			ContactId contactId) {
 		BlogInvitationResponse response = invitationFactory
 				.createInvitationResponse(m.getId(), m.getContactGroupId(),
 						m.getTimestamp(), false, false, true, false,
-						shareable, true);
+						true, m.getShareableId());
 		return new BlogInvitationResponseReceivedEvent(response, contactId);
 	}
 

briar-core/src/main/java/org/briarproject/briar/sharing/ForumInvitationFactoryImpl.java

@@ -30,10 +30,10 @@ public class ForumInvitationFactoryImpl
 	@Override
 	public ForumInvitationResponse createInvitationResponse(MessageId id,
 			GroupId contactGroupId, long time, boolean local, boolean sent,
-			boolean seen, boolean read, Forum forum, boolean accept) {
-		SessionId sessionId = new SessionId(forum.getId().getBytes());
+			boolean seen, boolean read, boolean accept, GroupId shareableId) {
+		SessionId sessionId = new SessionId(shareableId.getBytes());
 		return new ForumInvitationResponse(id, contactGroupId, time, local,
-				sent, seen, read, sessionId, forum, accept);
+				sent, seen, read, sessionId, accept, shareableId);
 	}
 
 }

briar-core/src/main/java/org/briarproject/briar/sharing/ForumProtocolEngineImpl.java

@@ -31,8 +31,7 @@ import static org.briarproject.briar.api.forum.ForumManager.MAJOR_VERSION;
 class ForumProtocolEngineImpl extends ProtocolEngineImpl<Forum> {
 
 	private final ForumManager forumManager;
-	private final InvitationFactory<Forum, ForumInvitationResponse>
-			invitationFactory;
+	private final InvitationFactory<Forum, ForumInvitationResponse> invitationFactory;
 
 	@Inject
 	ForumProtocolEngineImpl(DatabaseComponent db,
@@ -60,21 +59,21 @@ class ForumProtocolEngineImpl extends ProtocolEngineImpl<Forum> {
 
 	@Override
 	Event getInvitationResponseReceivedEvent(AcceptMessage m,
-			ContactId contactId, Forum shareable) {
+			ContactId contactId) {
 		ForumInvitationResponse response = invitationFactory
 				.createInvitationResponse(m.getId(), m.getContactGroupId(),
 						m.getTimestamp(), false, false, true, false,
-						shareable, true);
+						true, m.getShareableId());
 		return new ForumInvitationResponseReceivedEvent(response, contactId);
 	}
 
 	@Override
 	Event getInvitationResponseReceivedEvent(DeclineMessage m,
-			ContactId contactId, Forum shareable) {
+			ContactId contactId) {
 		ForumInvitationResponse response = invitationFactory
 				.createInvitationResponse(m.getId(), m.getContactGroupId(),
 						m.getTimestamp(), false, false, true, false,
-						shareable, true);
+						true, m.getShareableId());
 		return new ForumInvitationResponseReceivedEvent(response, contactId);
 	}
 

briar-core/src/main/java/org/briarproject/briar/sharing/InvitationFactory.java

@@ -4,17 +4,17 @@ import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.MessageId;
 import org.briarproject.briar.api.messaging.PrivateRequest;
-import org.briarproject.briar.api.messaging.PrivateResponse;
+import org.briarproject.briar.api.sharing.InvitationResponse;
 import org.briarproject.briar.api.sharing.Shareable;
 
-public interface InvitationFactory<S extends Shareable, I extends PrivateResponse<S>> {
+public interface InvitationFactory<S extends Shareable, R extends InvitationResponse> {
 
 	PrivateRequest<S> createInvitationRequest(boolean local, boolean sent,
 			boolean seen, boolean read, InviteMessage<S> m, ContactId c,
 			boolean available, boolean canBeOpened);
 
-	I createInvitationResponse(MessageId id,
-			GroupId contactGroupId, long time, boolean local, boolean sent,
-			boolean seen, boolean read, S shareable, boolean accept);
+	R createInvitationResponse(MessageId id, GroupId contactGroupId, long time,
+			boolean local, boolean sent, boolean seen, boolean read,
+			boolean accept, GroupId shareableId);
 
 }

briar-core/src/main/java/org/briarproject/briar/sharing/ProtocolEngineImpl.java

@@ -113,7 +113,13 @@ abstract class ProtocolEngineImpl<S extends Shareable>
 
 	private Message sendInviteMessage(Transaction txn, Session s,
 			@Nullable String message, long timestamp) throws DbException {
-		BdfList descriptor = getDescriptor(txn, s.getShareableId());
+		Group g = db.getGroup(txn, s.getShareableId());
+		BdfList descriptor;
+		try {
+			descriptor = clientHelper.toList(g.getDescriptor());
+		} catch (FormatException e) {
+			throw new DbException(e); // Invalid group descriptor
+		}
 		long localTimestamp = Math.max(timestamp, getLocalTimestamp(s));
 		Message m = messageEncoder.encodeInviteMessage(s.getContactGroupId(),
 				localTimestamp, s.getLastLocalMessageId(), descriptor, message);
@@ -287,7 +293,7 @@ abstract class ProtocolEngineImpl<S extends Shareable>
 		if (m.getTimestamp() <= s.getInviteTimestamp())
 			return abortWithMessage(txn, s);
 		// The dependency, if any, must be the last remote message
-		if (!isValidDependency(s, m.getPreviousMessageId()))
+		if (isInvalidDependency(s, m.getPreviousMessageId()))
 			return abortWithMessage(txn, s);
 		// Mark the invite message visible in the UI and (un)available to answer
 		markMessageVisibleInUi(txn, m.getId());
@@ -311,7 +317,7 @@ abstract class ProtocolEngineImpl<S extends Shareable>
 		if (m.getTimestamp() <= s.getInviteTimestamp())
 			return abortWithMessage(txn, s);
 		// The dependency, if any, must be the last remote message
-		if (!isValidDependency(s, m.getPreviousMessageId()))
+		if (isInvalidDependency(s, m.getPreviousMessageId()))
 			return abortWithMessage(txn, s);
 		// Mark the invite message visible in the UI and unavailable to answer
 		markMessageVisibleInUi(txn, m.getId());
@@ -358,7 +364,7 @@ abstract class ProtocolEngineImpl<S extends Shareable>
 		if (m.getTimestamp() <= s.getInviteTimestamp())
 			return abortWithMessage(txn, s);
 		// The dependency, if any, must be the last remote message
-		if (!isValidDependency(s, m.getPreviousMessageId()))
+		if (isInvalidDependency(s, m.getPreviousMessageId()))
 			return abortWithMessage(txn, s);
 		// Mark the response visible in the UI
 		markMessageVisibleInUi(txn, m.getId());
@@ -367,8 +373,7 @@ abstract class ProtocolEngineImpl<S extends Shareable>
 				m.getTimestamp(), false);
 		// Broadcast an event
 		ContactId contactId = getContactId(txn, m.getContactGroupId());
-		S shareable = getShareable(txn, s.getShareableId());
-		txn.attach(getInvitationResponseReceivedEvent(m, contactId, shareable));
+		txn.attach(getInvitationResponseReceivedEvent(m, contactId));
 		// Move to the next state
 		return new Session(nextState, s.getContactGroupId(), s.getShareableId(),
 				s.getLastLocalMessageId(), m.getId(), s.getLocalTimestamp(),
@@ -386,7 +391,7 @@ abstract class ProtocolEngineImpl<S extends Shareable>
 	}
 
 	abstract Event getInvitationResponseReceivedEvent(AcceptMessage m,
-			ContactId contactId, S shareable);
+			ContactId contactId);
 
 	@Override
 	public Session onDeclineMessage(Transaction txn, Session s,
@@ -411,7 +416,7 @@ abstract class ProtocolEngineImpl<S extends Shareable>
 		if (m.getTimestamp() <= s.getInviteTimestamp())
 			return abortWithMessage(txn, s);