From afc0d3aa27c7fdc73b57e980b11e58ce93660c4d Mon Sep 17 00:00:00 2001
From: Johannes Schriewer <hallo@dunkelstern.de>
Date: Mon, 30 Jul 2018 22:20:10 +0200
Subject: [PATCH] Bugfix: Do not allow DUP flag for QoS 0

Re #11
---
 src/packet.c          |  5 +++++
 tests/encode_packet.c | 20 ++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/src/packet.c b/src/packet.c
index d80ba8c..9ab55b1 100644
--- a/src/packet.c
+++ b/src/packet.c
@@ -475,6 +475,11 @@ Buffer *encode_publish(PublishPayload *payload) {
     }
     buffer->data[buffer->position - 2] |= (payload->qos << 1);
     if (payload->duplicate) {
+        if (payload->qos == MQTT_QOS_0) {
+            DEBUG_LOG("You can not set a DUP flag for QoS Level 0.");
+            buffer_release(buffer);
+            return NULL;
+        }
         buffer->data[buffer->position - 2] |= 8;
     }
 
diff --git a/tests/encode_packet.c b/tests/encode_packet.c
index 42dbfbb..52970da 100644
--- a/tests/encode_packet.c
+++ b/tests/encode_packet.c
@@ -274,6 +274,25 @@ TestResult test_encode_publish_no_msg(void) {
     );
 }
 
+TestResult test_encode_publish_dup_qos0(void) {
+    char data[] = {
+        0x33, 0x0e, // header, qos1, retain
+        0x00, 0x0a, 't', 'e', 's', 't', '/', 't', 'o', 'p', 'i', 'c',
+        0x00, 0x0a // packet id
+    };
+    PublishPayload *payload = calloc(1, sizeof(PublishPayload));
+
+    payload->qos = MQTT_QOS_0;
+    payload->duplicate = true;
+    payload->retain = true;
+    payload->topic = "test/topic";
+    payload->packet_id = 10;
+
+    Buffer *encoded = mqtt_packet_encode(&(MQTTPacket){ PacketTypePublish, payload });
+    free(payload);
+    TESTASSERT(encoded == NULL, "DUP and QoS level 0 is an incompatible combination");
+}
+
 TestResult test_encode_publish_with_msg(void) {
     char data[] = {
         0x3b, 0x15, // header, qos1, retain
@@ -511,6 +530,7 @@ TESTS(
     TEST("Encode Connect with auth", test_encode_connect_auth),
     TEST("Encode ConnAck", test_encode_connack),
     TEST("Encode Publish with no message", test_encode_publish_no_msg),
+    TEST("Encode Publish with invalid flags", test_encode_publish_dup_qos0),
     TEST("Encode Publish with message", test_encode_publish_with_msg),
     TEST("Encode PubAck", test_encode_puback),
     TEST("Encode PubRec", test_encode_pubrec),