1 files changed, 47 insertions, 0 deletions
diff --git a/src/lib-imap/imap-keepalive.c b/src/lib-imap/imap-keepalive.c
new file mode 100644
index 0000000..0756ce8
--- /dev/null
+++ b/src/lib-imap/imap-keepalive.c
@@ -0,0 +1,47 @@
+/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "crc32.h"
+#include "net.h"
+#include "imap-keepalive.h"
+
+#include <time.h>
+
+static bool imap_remote_ip_is_usable(const struct ip_addr *ip)
+{
+	unsigned int addr;
+
+	if (ip->family == 0)
+		return FALSE;
+	if (ip->family == AF_INET) {
+#define IP4(a,b,c,d) ((unsigned)(a)<<24|(unsigned)(b)<<16|(unsigned)(c)<<8|(unsigned)(d))
+		addr = ip->u.ip4.s_addr;
+		if (addr >= IP4(10,0,0,0) && addr <= IP4(10,255,255,255))
+			return FALSE; /* 10/8 */
+		if (addr >= IP4(192,168,0,0) && addr <= IP4(192,168,255,255))
+			return FALSE; /* 192.168/16 */
+		if (addr >= IP4(172,16,0,0) && addr <= IP4(172,31,255,255))
+			return FALSE; /* 172.16/12 */
+		if (addr >= IP4(127,0,0,0) && addr <= IP4(127,255,255,255))
+			return FALSE; /* 127/8 */
+#undef IP4
+	}
+	else if (ip->family == AF_INET6) {
+		addr = ip->u.ip6.s6_addr[0];
+		if (addr == 0xfc || addr == 0xfd)
+			return FALSE; /* fc00::/7 */
+	}
+	return TRUE;
+}
+
+unsigned int
+imap_keepalive_interval_msecs(const char *username, const struct ip_addr *ip,
+			      unsigned int interval_secs)
+{
+	unsigned int client_hash;
+
+	client_hash = ip != NULL && imap_remote_ip_is_usable(ip) ?
+		net_ip_hash(ip) : crc32_str(username);
+	interval_secs -= (time(NULL) + client_hash) % interval_secs;
+	return interval_secs * 1000;
+}