imap.c: Add support for RFC 5465 NOTIFY.

Add support for NOTIFY, so that we can receive updates about
new mail in folders besides the currently selected one. We
already handled STATUS in IDLE responses, so we just needed
to add the code to enable the NOTIFY extension appropriately.

As part of this change, we also treat INBOX folders case-insensitively,
as in InterLinked1/wssmail@e454859.

This change (and the referenced one) are needed to account for
scenarios such as when Other Users.example.Inbox appear in the
LIST response and navigation, but STATUS updates use a different
case, e.g. Other Users.example.INBOX.

Author: InterLinked1

.github/workflows/main.yml

@@ -76,6 +76,9 @@ jobs:
        uses: actions/checkout@v4
      - name: Start build
        run: |
+          sed -i 's|deb.debian.org/debian buster main|archive.debian.org/debian buster main|g' /etc/apt/sources.list
+          sed -i 's|deb.debian.org/debian buster-updates main|archive.debian.org/debian buster-updates main|g' /etc/apt/sources.list
+          sed -i 's|deb.debian.org/debian-security buster/updates main|archive.debian.org/debian-security buster/updates main|g' /etc/apt/sources.list
           apt-get update
           apt-get install -y git wget automake pkg-config libtool m4 build-essential libncurses-dev
           cd ..

imap.c

@@ -387,7 +387,7 @@ static void list_status_logger(mailstream *imap_stream, int log_type, const char
 		return;
 	}
 
-	/* Can be broken up across multiple log callback calls, so append to a dynstr */
+	/* Can be broken up across multiple log callback calls */
 	client_debug(6, "Log callback of %lu bytes for LIST-STATUS", size);
 	/* Since this can take quite a bit of time, send an update here */
 	/* Look for "* STATUS " */
@@ -875,6 +875,7 @@ static int __client_list(struct client *client)
 	clist *imap_list;
 	int res, i;
 	int needunselect = 0;
+	int numother = 0;
 	/* This is a single-threaded application, so there is no concurrency risk to making this static/global,
 	 * and it's probably better to put such a large buffer in the global segment rather than on the stack. */
 	static char list_status_buf[32768]; /* Hopefully big enough to fit the entire LIST-STATUS response */
@@ -956,6 +957,10 @@ static int __client_list(struct client *client)
 			client->delimiter = mb_list->mb_delimiter;
 			client->mailboxes[i].name = strdup(name);
 
+			if (IMAP_HAS_CAPABILITY(client, IMAP_CAPABILITY_NOTIFY) && !strncmp(name, "Other Users.", STRLEN("Other Users."))) {
+				numother++;
+			}
+
 			if (client->mailboxes[i].flags & IMAP_MAILBOX_NOSELECT) {
 				continue;
 			}
@@ -1019,6 +1024,53 @@ static int __client_list(struct client *client)
 		free(mb_names);
 	}
 
+	if (IMAP_HAS_CAPABILITY(client, IMAP_CAPABILITY_NOTIFY)) {
+		char cmd[2048];
+		char buf[sizeof(cmd) - 147];
+		int bytes = 0;
+		int otherinboxonly = numother > 10;
+
+#define OTHER_USERS_WATCHALL_THRESHOLD 25
+
+		if (numother > OTHER_USERS_WATCHALL_THRESHOLD) {
+			clistiter *cur;
+			for (cur = clist_begin(imap_list); cur; cur = clist_next(cur)) {
+				struct mailimap_mailbox_list *mb_list = clist_content(cur);
+				const char *name = mb_list->mb_name;
+				if (!strncmp(name, "Other Users.", STRLEN("Other Users."))) {
+					if (otherinboxonly && !strcasestr(name, "INBOX")) {
+						continue;
+					}
+				} else if (!strncmp(name, "Shared Folders.", STRLEN("Shared Folders."))) {
+					if (!strcasestr(name, "INBOX")) {
+						continue;
+					}
+				} else {
+					continue; /* Personal namespace */
+				}
+				bytes += snprintf(buf + bytes, sizeof(buf) - bytes, " %c%s%c", '"', name, '"');
+				if ((size_t) bytes >= sizeof(buf)) {
+					client_warning("Truncation occured when building NOTIFY command");
+					break;
+				}
+			}
+		}
+
+		/* We just want notifications when something happens, having an untagged FETCH sent to us isn't that important.
+		 * We can wake up and do some work if really needed. */
+		if (bytes > 0 && (size_t) bytes <= sizeof(buf)) {
+			snprintf(cmd, sizeof(cmd), "NOTIFY SET (SELECTED-DELAYED (MessageNew MessageExpunge FlagChange)) %s(personal (MessageNew MessageExpunge)) (mailboxes%s (MessageNew MessageExpunge))",
+				numother <= OTHER_USERS_WATCHALL_THRESHOLD ? "(subtree \"Other Users\" (MessageNew MessageExpunge FlagChange))" : "",
+				buf);
+		} else {
+			snprintf(cmd, sizeof(cmd), "NOTIFY SET (SELECTED-DELAYED (MessageNew MessageExpunge FlagChange)) (personal (MessageNew MessageExpunge))%s", numother ? " (subtree \"Other Users\" (MessageNew MessageExpunge))" : "");
+		}
+		res = mailimap_custom_command(client->imap, cmd);
+		if (MAILIMAP_ERROR(res)) {
+			client_warning("NOTIFY SET failed\n");
+		}
+	}
+
 	if (needunselect) {
 		/* UNSELECT itself is an extension. Only do if supported. */
 		if (IMAP_HAS_CAPABILITY(client, IMAP_CAPABILITY_UNSELECT)) {
@@ -1325,13 +1377,31 @@ static inline void masquerade_mailbox(struct mailbox *restrict new_mbox, struct
 #undef COPY_MBOX_FIELD
 }
 
+static int str_case_ends_with(const char *str, const char *suffix)
+{
+	size_t str_len;
+	size_t suffix_len;
+
+	str_len = strlen(str);
+	suffix_len = strlen(suffix);
+
+	return str_len >= suffix_len && !strcasecmp(str + str_len - suffix_len, suffix);
+}
+
 static struct mailbox *find_mailbox_by_name(struct client *client, const char *name)
 {
 	int i;
 	for (i = 0; i < client->num_mailboxes; i++) {
+		/* In IMAP, mailbox names are case-sensitive...
+		 * (even though most server implementations are case-insensitive, we can't assume that) */
 		if (!strcmp(client->mailboxes[i].name, name)) {
 			return &client->mailboxes[i];
 		}
+		/* ... except for INBOX (RFC 3501 5.1)
+		 * We do case-insensitive matches for INBOX, as well as any subfolder named "INBOX". */
+		if ((!strcasecmp(name, "INBOX") || str_case_ends_with(name, ".INBOX")) && !strcasecmp(client->mailboxes[i].name, name)) {
+			return &client->mailboxes[i];
+		}
 	}
 	return NULL;
 }