Feature/zeroing rx buffer remain (#90)

* Added zeroing rx buffer remain

* Added zeroing rx buffer remain

* Added safety margin for the rx-buffer in the different ports.

* Added safety margin for the receive buffer.

* Added DoxyGen comments.

* Fixed checking return value when calculating distance between opening and closing tag on multiple properties.

ports/arduino_uno/bip.c

@@ -244,6 +244,7 @@ uint16_t bip_receive(BACNET_ADDRESS *src, /* source address */
     unsigned timeout)
 {
     int received_bytes = 0;
+    int max = 0;
     uint16_t pdu_len = 0; /* return value */
     uint8_t src_addr[] = { 0, 0, 0, 0 };
     uint16_t src_port = 0;
@@ -274,6 +275,18 @@ uint16_t bip_receive(BACNET_ADDRESS *src, /* source address */
     if (pdu[0] != BVLL_TYPE_BACNET_IP)
         return 0;
 
+    /* Erase up to 16 bytes after the received bytes as safety margin to
+     * ensure that the decoding functions will run into a 'safe field'
+     * of zero, if for any reason they would overrun, when parsing the
+     * message. */
+    max = (int)max_pdu - received_bytes;
+    if (max > 0) {
+        if (max > 16) {
+            max = 16;
+        }
+        memset(&pdu[received_bytes], 0, max);
+    }
+
     if (bvlc_for_non_bbmd(src_addr, &src_port, pdu, received_bytes) > 0) {
         /* Handled, usually with a NACK. */
 #if PRINT_ENABLED

ports/arduino_uno/main.c

@@ -70,7 +70,17 @@ void setup()
 #endif
 }
 
-static uint8_t PDUBuffer[MAX_MPDU];
+/** Static receive buffer, initialized with zeros by the C Library Startup Code. */
+
+static uint8_t PDUBuffer[MAX_MPDU + 16 /* Add a little safety margin to the buffer,
+                                        * so that in the rare case, the message
+                                        * would be filled up to MAX_MPDU and some
+                                        * decoding functions would overrun, these
+                                        * decoding functions will just end up in
+                                        * a safe field of static zeros. */];
+
+/** Main */
+
 int main(void)
 {
     uint16_t pdu_len = 0;
@@ -84,7 +94,7 @@ int main(void)
     for (;;) {
         /* other tasks */
         /* BACnet handling */
-        pdu_len = datalink_receive(&src, &PDUBuffer[0], sizeof(PDUBuffer), 0);
+        pdu_len = datalink_receive(&src, &PDUBuffer[0], MAX_MPDU, 0);
         if (pdu_len) {
             npdu_handler(&src, &PDUBuffer[0], pdu_len);
         }