gateway_protocol/gateway_protocol.c

 #include <gateway_protocol/gateway_protocol.h>
 
+#define GATEWAY_PROTOCOL_APP_KEY_SIZE       8
+
+static uint8_t app_key[GATEWAY_PROTOCOL_APP_KEY_SIZE];
+static uint8_t dev_id = 0xFF;
+
+void gateway_protocol_init(const uint8_t *appkey, const uint8_t devid) {
+    memcpy(app_key, appkey, GATEWAY_PROTOCOL_APP_KEY_SIZE);
+    dev_id = devid;
+}
 
 void gateway_protocol_packet_encode (
-    const uint8_t dev_id, 
     const gateway_protocol_packet_type_t packet_type,
     const uint8_t payload_length,
     const uint8_t *payload,
@@ -11,18 +19,23 @@ void gateway_protocol_packet_encode (
 {
     *packet_length = 0;
 
+    memcpy(&packet[*packet_length], app_key, GATEWAY_PROTOCOL_APP_KEY_SIZE);
+    (*packet_length) += GATEWAY_PROTOCOL_APP_KEY_SIZE;
+
     packet[*packet_length] = dev_id;
-    packet_length++;
+    (*packet_length)++;
 
     packet[*packet_length] = packet_type;
     (*packet_length)++;
 
+    packet[*packet_length] = payload_length;
+    (*packet_length)++;
+
     memcpy(&packet[*packet_length], payload, payload_length);
-    *packet_length += payload_length;
+    (*packet_length) += payload_length;
 }
 
 uint8_t gateway_protocol_packet_decode (
-    uint8_t *dev_id, 
     gateway_protocol_packet_type_t *packet_type,
     uint8_t *payload_length,
     uint8_t *payload,
@@ -30,17 +43,25 @@ uint8_t gateway_protocol_packet_decode (
     const uint8_t *packet)
 {
     uint8_t p_len = 0;
+    uint8_t appkey[GATEWAY_PROTOCOL_APP_KEY_SIZE];
+    uint8_t dev;
 
-    *dev_id = packet[p_len];
+    memcpy(appkey, &packet[p_len], GATEWAY_PROTOCOL_APP_KEY_SIZE);
+    p_len += GATEWAY_PROTOCOL_APP_KEY_SIZE;
+
+    dev = packet[p_len];
     p_len++;
 
     *packet_type = (gateway_protocol_packet_type_t) packet[p_len];
     p_len++;
 
+    p_len++;
     *payload_length = packet_length - p_len;
 
     memcpy(payload, &packet[p_len], *payload_length);
     p_len += *payload_length;
 
-    return (p_len == packet_length);
+    return (memcmp(appkey, app_key, GATEWAY_PROTOCOL_APP_KEY_SIZE) && 
+            dev == dev_id &&
+            p_len == packet_length);
 }
\ No newline at end of file

gateway_protocol/gateway_protocol.h

@@ -26,8 +26,9 @@ typedef enum {
     GATEWAY_PROTOCOL_STAT_NACK = 0xFF
 } gateway_protocol_stat_t;
 
+void gateway_protocol_init(const uint8_t *appkey, const uint8_t devid);
+
 void gateway_protocol_packet_encode (
-    const uint8_t dev_id, 
     const gateway_protocol_packet_type_t packet_type,
     const uint8_t payload_length,
     const uint8_t *payload,
@@ -35,7 +36,6 @@ void gateway_protocol_packet_encode (
     uint8_t *packet);
 
 uint8_t gateway_protocol_packet_decode (
-    uint8_t *dev_id, 
     gateway_protocol_packet_type_t *packet_type,
     uint8_t *payload_length,
     uint8_t *payload,