[ENHANCEMENT] Allow disable threads

This changeset will not alter thread categorisation which works decently today but only thread presentation
to the end user which is currently relying on search. As an operator I wishes to have a security trigger
if things go blur.

Author: chibenwa

mailbox/cassandra/src/main/java/org/apache/james/mailbox/cassandra/CassandraThreadIdGuessingAlgorithm.java

@@ -48,6 +48,8 @@
 import reactor.core.publisher.Mono;
 
 public class CassandraThreadIdGuessingAlgorithm implements ThreadIdGuessingAlgorithm {
+    private static final boolean DISABLE_THREADS = Boolean.valueOf(System.getProperty("james.mailbox.threads.disable", "false"));
+
     private final MailboxManager mailboxManager;
     private final CassandraThreadDAO threadDAO;
     private final CassandraThreadLookupDAO threadLookupDAO;
@@ -82,6 +84,10 @@ public Mono<ThreadId> guessThreadIdReactive(MessageId messageId, Optional<MimeMe
 
     @Override
     public Flux<MessageId> getMessageIdsInThread(ThreadId threadId, MailboxSession session) {
+        if (DISABLE_THREADS) {
+            return Flux.just(threadId.getBaseMessageId());
+        }
+
         SearchQuery searchQuery = SearchQuery.builder()
             .andCriteria(SearchQuery.threadId(threadId))
             .sorts(new SearchQuery.Sort(SearchQuery.Sort.SortClause.Arrival, SearchQuery.Sort.Order.NATURAL))

mailbox/postgres/src/main/java/org/apache/james/mailbox/postgres/PostgresThreadIdGuessingAlgorithm.java

@@ -44,6 +44,8 @@
 import reactor.core.publisher.Mono;
 
 public class PostgresThreadIdGuessingAlgorithm implements ThreadIdGuessingAlgorithm {
+    private static final boolean DISABLE_THREADS = Boolean.valueOf(System.getProperty("james.mailbox.threads.disable", "false"));
+
     private final PostgresThreadDAO.Factory threadDAOFactory;
 
     @Inject
@@ -76,6 +78,10 @@ public Mono<ThreadId> guessThreadIdReactive(MessageId messageId, Optional<MimeMe
 
     @Override
     public Flux<MessageId> getMessageIdsInThread(ThreadId threadId, MailboxSession session) {
+        if (DISABLE_THREADS) {
+            return Flux.just(threadId.getBaseMessageId());
+        }
+
         PostgresThreadDAO threadDAO = threadDAOFactory.create(session.getUser().getDomainPart());
         return threadDAO.findMessageIds(threadId, session.getUser())
             .switchIfEmpty(Flux.error(new ThreadNotFoundException(threadId)));