there is no packet ID in mqtt publish packets for QoS 0 publish

diff --git a/lib/protocols/mqtt.c b/lib/protocols/mqtt.c
index d11a809..d0a62d4 100644 (file)
--- a/lib/protocols/mqtt.c
+++ b/lib/protocols/mqtt.c
@@ -253,10 +253,14 @@ int mqtt_pack_publish_packet(const struct mqtt_publish_pkt* pkt, uint8_t* buf, u
                return -ENODATA;
        }
        /* Compute message size
-        * Packet ID is 2 bytes long. There is no "message size" field in the publish packet, as the
-        * message size can be computed by substracting the topic string size and packet id size from
-        * the packet "remaining length" field. */
-       remaining_length = 2 + pkt->message_size;
+        * There is no "message size" field in the publish packet, as the message size can be computed by
+        * substracting the topic string size and packet id size from the packet "remaining length" field.
+        */
+       remaining_length = pkt->message_size;
+       /* Packet ID is 2 bytes long. If QoS is 0, then the packet must not include a packet ID */
+       if (pkt->topic.QoS != 0) {
+               remaining_length += 2;
+       }
        /* Topic is mandatory */
        if (pkt->topic.name == NULL) {
                return -EINVAL;
@@ -283,9 +287,11 @@ int mqtt_pack_publish_packet(const struct mqtt_publish_pkt* pkt, uint8_t* buf, u
        /* Topic is mandatory */
        len += mqtt_pack_str((buf + len), pkt->topic.name, topic_len);
        /* Packet ID */
-       tmp_packet_id = htons(pkt->packet_id);
-       memcpy((buf + len), &tmp_packet_id, 2);
-       len += 2;
+       if (pkt->topic.QoS != 0) {
+               tmp_packet_id = htons(pkt->packet_id);
+               memcpy((buf + len), &tmp_packet_id, 2);
+               len += 2;
+       }
        /* Add optionnal application message */
        if (pkt->message_size != 0) {
                memcpy((buf + len), pkt->application_message, pkt->message_size);
@@ -334,13 +340,20 @@ int mqtt_unpack_publish_packet(struct mqtt_publish_pkt* pkt, uint8_t* buf, uint3
        topic_len = ntohs(tmp);
        pkt->topic.name = (char*)(buf + idx + 2);
        idx += topic_len + 2;
-       if ((idx + 2) > size) {
+       /* Does it fit in the remaining length ? */
+       tmp = idx;
+       if (pkt->topic.QoS != 0) {
+               tmp += 2;
+       }
+       if (tmp > size) {
                return -EPROTO;
        }
        /* Decode packet ID */
-       idx += 2;
+       if (pkt->topic.QoS != 0) {
                memcpy(&tmp, (buf + idx), 2);
                pkt->packet_id = ntohs(tmp);
+               idx += 2;
+       }
        /* Get application message */
        pkt->message_size = size - idx;
        if (pkt->message_size != 0) {