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/bsd/bip-init.c

@@ -319,7 +319,7 @@ uint16_t bip_receive(
     max = BIP_Socket;
     /* see if there is a packet for us */
     if (select(max + 1, &read_fds, NULL, NULL, &select_timeout) > 0) {
-        received_bytes = recvfrom(BIP_Socket, (char *)&npdu[0], max_npdu, 0,
+        received_bytes = recvfrom(max, (char *)&npdu[0], max_npdu, 0,
             (struct sockaddr *)&sin, &sin_len);
     } else {
         return 0;
@@ -336,6 +336,17 @@ uint16_t bip_receive(
     if (npdu[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_npdu - received_bytes;
+    if (max > 0) {
+        if (max > 16) {
+            max = 16;
+        }
+        memset(&npdu[received_bytes], 0, max);
+    }
     /* Data link layer addressing between B/IPv4 nodes consists of a 32-bit
        IPv4 address followed by a two-octet UDP port number (both of which
        shall be transmitted with the most significant octet first). This

ports/bsd/main.c

@@ -51,8 +51,14 @@
 
 bool Who_Is_Request = true;
 
-/* buffers used for receiving */
-static uint8_t Rx_Buf[MAX_MPDU] = { 0 };
+/** Static receive buffer, initialized with zeros by the C Library Startup Code. */
+
+static uint8_t Rx_Buf[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. */] = { 0 };
 
 static void LocalIAmHandler(
     uint8_t *service_request, uint16_t service_len, BACNET_ADDRESS *src)