net_imap: Skip generate_mailbox_name for exclusive proxying sessions.

When sending untagged FETCH, EXISTS, etc. responses, we call
generate_mailbox_name to generate the name of a mailbox as it would
appear for a user (to handle shared/public mailboxes that may have
different names for different users).

If a user has a lot of exclusive proxying connections, we generate
the mailbox name for that user each loop iteration, but then when
we call imap_notify_applicable, the answer will be "no" because
exclusively proxying sessions don't create NOTIFY watches locally.

As an optimization, we can therefore simply skip that session entirely
if it's exclusively proxying.

Also indicate in the "imap sessions" CLI command if a session is
exclusively proxying. Previously the output reported "No" since
imap->client is not set, but this is incorrect. We now use the dedicated
flag to distinguish between exclusively proxying sessions and normal
sessions that just happen to have a proxying client in the foreground.

LBBS-140 #close

Author: InterLinked1

nets/net_imap.c

@@ -260,7 +260,7 @@ static int cli_imap_sessions(struct bbs_cli_args *a)
 			}
 		}
 		bbs_dprintf(a->fdout, "%4u %14p %4s %7s %11s %-28s %s\n",
-			imap->node->id, imap, BBS_YN(imap->idle), imap->client ? "Yes" : "No", S_IF(mbox_name), S_IF(imap->folder), S_IF(imap->clientid));
+			imap->node->id, imap, BBS_YN(imap->idle), imap->exclusiveproxy ? "Excl." : imap->client ? "Yes" : "No", S_IF(mbox_name), S_IF(imap->folder), S_IF(imap->clientid));
 	}
 	RWLIST_UNLOCK(&sessions);
 	return 0;
@@ -502,6 +502,9 @@ void send_untagged_fetch(struct imap_session *imap, const char *maildir, int seq
 		if (s == imap) { /* Skip if the update was caused by the client. The STORE handler already sent a response to this client if needed. */
 			continue;
 		}
+		if (s->exclusiveproxy) {
+			continue; /* Skip if this IMAP session is exclusively proxying */
+		}
 		/* imap->folder is maybe not the same name for s.
 		 * We convert the maildir path to the name for s, though this is a little bit roundabout.
 		 * Would be easier if generate_status could accept a maildir as well instead of just a name.
@@ -559,6 +562,9 @@ static void send_untagged_expunge(struct bbs_node *node, struct mailbox *mbox, c
 		if (s->node == node && silent) {
 			continue;
 		}
+		if (s->exclusiveproxy) {
+			continue; /* Skip if this IMAP session is exclusively proxying */
+		}
 		/* We can't pass the mailbox name into send_untagged_expunge anyways,
 		 * because mailbox names might be different for different users (e.g. Other Users) */
 		if (generate_mailbox_name(s, maildir, mboxname, sizeof(mboxname))) {
@@ -637,6 +643,10 @@ static void send_untagged_exists(struct bbs_node *node, struct mailbox *mbox, co
 		char mboxname[256];
 		const char *fetchargs = NULL;
 
+		if (s->exclusiveproxy) {
+			continue; /* Skip if this IMAP session is exclusively proxying */
+		}
+
 		if (generate_mailbox_name(s, maildir, mboxname, sizeof(mboxname))) {
 			continue;
 		}
@@ -715,6 +725,9 @@ static void send_untagged_list(struct bbs_node *node, enum mailbox_event_type ty
 			/* RFC 5465 Section 5: avoid notifying client if this was caused by that client */
 			continue;
 		}
+		if (s->exclusiveproxy) {
+			continue; /* Skip if this IMAP session is exclusively proxying */
+		}
 
 		/* Mailbox names could be different for different users, so need to do per session, not just once */
 		if (generate_mailbox_name(s, maildir, newdir, sizeof(newdir))) {
@@ -767,6 +780,9 @@ static void send_untagged_uidvalidity(struct mailbox *mbox, const char *maildir,
 	/* Notify anyone watching this mailbox, specifically the INBOX. */
 	RWLIST_RDLOCK(&sessions);
 	RWLIST_TRAVERSE(&sessions, s, entry) {
+		if (s->exclusiveproxy) {
+			continue; /* Skip if this IMAP session is exclusively proxying */
+		}
 		if (s->mbox != mbox || strcmp(s->dir, maildir)) {
 			continue;
 		}

nets/net_imap/imap.h

@@ -90,6 +90,7 @@ struct imap_session {
 	unsigned int innew:1;		/* So we can use the same callback for both new and cur */
 	unsigned int readonly:1;	/* SELECT vs EXAMINE */
 	unsigned int inauth:1;
+	unsigned int exclusiveproxy:1; /* Whether this connection is exclusively proxying to another IMAP server */
 	unsigned int idle:1;		/* Whether IDLE is active */
 	unsigned int dnd:1;			/* Do Not Disturb: Whether client is executing a FETCH, STORE, or SEARCH command (EXPUNGE responses are not allowed). XXX Unused? */
 	unsigned int pending:1;		/* Delayed output is pending in pfd pipe */

nets/net_imap/imap_client.c

@@ -1240,6 +1240,7 @@ int imap_proxy_remote_mailbox_exclusively(struct imap_session *imap, const char
 		}
 	}
 
+	imap->exclusiveproxy = 1;
 	bbs_verb(4, "Beginning exclusively proxied session with remote mailbox '%s'\n", name);
 
 	/* The client expects a CAPABILITY response after authenticating successfully,
@@ -1312,6 +1313,7 @@ int imap_proxy_remote_mailbox_exclusively(struct imap_session *imap, const char
 	}
 
 cleanup:
+	imap->exclusiveproxy = 0;
 	imap_client_unlink(imap, client);
 	return -1;
 }