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Address Race-Condition when Two Contacts Share Same Forum

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with each other at the same time.

Closes #388
This commit is contained in:
Torsten Grote
2016-05-30 16:59:26 -03:00
parent bba7083660
commit 4acb59b22a
2 changed files with 127 additions and 18 deletions
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43
briar-core/src/org/briarproject/forum/ForumSharingManagerImpl.java
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@@ -27,6 +27,7 @@ import org.briarproject.api.forum.ForumFactory;
import org.briarproject.api.forum.ForumInvitationMessage;
import org.briarproject.api.forum.ForumManager;
import org.briarproject.api.forum.ForumSharingManager;
import org.briarproject.api.identity.LocalAuthor;
import org.briarproject.api.sync.ClientId;
import org.briarproject.api.sync.Group;
import org.briarproject.api.sync.GroupId;
@@ -206,7 +207,7 @@ class ForumSharingManagerImpl extends BdfIncomingMessageHook
ContactId contactId = getContactId(txn, m.getGroupId());
Contact contact = db.getContact(txn, contactId);
if (!canBeShared(txn, f.getId(), contact))
throw new FormatException();
checkForRaceCondition(txn, f, contact);
// initialize state and process invitation
InviteeSessionState state =
@@ -488,6 +489,46 @@ class ForumSharingManagerImpl extends BdfIncomingMessageHook
}
}
private void checkForRaceCondition(Transaction txn, Forum f, Contact c)
throws FormatException, DbException {
GroupId contactGroup = getContactGroup(c).getId();
if (!listContains(txn, contactGroup, f.getId(), TO_BE_SHARED_BY_US))
// no race-condition, this invitation is invalid
throw new FormatException();
// we have an invitation race condition
LocalAuthor author = db.getLocalAuthor(txn, c.getLocalAuthorId());
Bytes ourKey = new Bytes(author.getPublicKey());
Bytes theirKey = new Bytes(c.getAuthor().getPublicKey());
// determine which invitation takes precedence
boolean alice = ourKey.compareTo(theirKey) < 0;
if (alice) {
// our own invitation takes precedence, so just delete Bob's
LOG.info("Invitation race-condition: We are Alice deleting Bob's invitation.");
throw new FormatException();
} else {
// we are Bob, so we need to "take back" our own invitation
LOG.info("Invitation race-condition: We are Bob taking back our invitation.");
ForumSharingSessionState state =
getSessionStateForLeaving(txn, f, c.getId());
if (state instanceof SharerSessionState) {
//SharerEngine engine = new SharerEngine();
//processSharerStateUpdate(txn, null,
// engine.onLocalAction((SharerSessionState) state,
// Action.LOCAL_LEAVE));
// simply remove from list instead of involving engine
removeFromList(txn, contactGroup, TO_BE_SHARED_BY_US, f);
// TODO here we could also remove the old session state
// and invitation message
}
}
}
private SharerSessionState initializeSharerState(Transaction txn, Forum f,
ContactId contactId) throws FormatException, DbException {