dtls: ensure that the DTLS window doesn't get stalled

That is ensure that it is forwarded at least one place if more than 16
packets have been received since the first one.

1 files changed, 9 insertions, 1 deletions

diff --git a/lib/dtls-sw.c b/lib/dtls-sw.c
index 616bd5a868..8c334c05af 100644
--- a/lib/dtls-sw.c
+++ b/lib/dtls-sw.c
@@ -51,7 +51,15 @@
 
 #define DTLS_WINDOW_MARK(W, S)		((W)->dtls_sw_bits |= ((uint64_t) 1 << DTLS_WINDOW_OFFSET(W, S)))
 
-#define DTLS_WINDOW_UPDATE(W)		while ((W)->dtls_sw_bits & (uint64_t) 1) { \
+/* We forcefully advance the window once we have received more than
+ * 8 packets since the first one. That way we ensure that we don't
+ * get stuck on connections with many lost packets. */
+#define DTLS_WINDOW_UPDATE(W)		\
+					if (((W)->dtls_sw_bits & 0xffffffffffff0000LL) != 0) { \
+						(W)->dtls_sw_bits = (W)->dtls_sw_bits >> 1; \
+						(W)->dtls_sw_start++; \
+					} \
+					while ((W)->dtls_sw_bits & (uint64_t) 1) { \
 						(W)->dtls_sw_bits = (W)->dtls_sw_bits >> 1; \
 						(W)->dtls_sw_start++; \
 					}