randomize tcp source port for #1800

Author: nickzoic

shared-module/network/__init__.c

@@ -99,3 +99,7 @@ void network_module_create_random_mac_address(uint8_t *mac) {
     mac[4] = (uint8_t)(rb2 >> 8);
     mac[5] = (uint8_t)(rb2);
 }
+
+uint16_t network_module_create_random_source_tcp_port(void) {
+    return 0xc000 | shared_modules_random_getrandbits(14);
+}

shared-module/network/__init__.h

@@ -25,11 +25,12 @@
  * THE SOFTWARE.
  */
 
-void network_module_create_random_mac_address(uint8_t *mac);
-
 #ifndef MICROPY_INCLUDED_SHARED_MODULE_NETWORK___INIT___H
 #define MICROPY_INCLUDED_SHARED_MODULE_NETWORK___INIT___H
 
+void network_module_create_random_mac_address(uint8_t *mac);
+uint16_t network_module_create_random_source_tcp_port(void);
+
 #define MOD_NETWORK_IPADDR_BUF_SIZE (4)
 
 #define MOD_NETWORK_AF_INET (2)

shared-module/wiznet/wiznet5k.c

@@ -203,8 +203,12 @@ int wiznet5k_socket_accept(mod_network_socket_obj_t *socket, mod_network_socket_
 }
 
 int wiznet5k_socket_connect(mod_network_socket_obj_t *socket, byte *ip, mp_uint_t port, int *_errno) {
+    uint16_t src_port = network_module_create_random_source_tcp_port();
+    // make sure same outgoing port number can't be in use by two different sockets.
+    src_port = (src_port & ~(_WIZCHIP_SOCK_NUM_ - 1)) | socket->u_param.fileno;
+
     // use "bind" function to open the socket in client mode
-    if (wiznet5k_socket_bind(socket, ip, 0, _errno) != 0) {
+    if (wiznet5k_socket_bind(socket, NULL, src_port, _errno) != 0) {
         return -1;
     }