net_device: re-factor code so as to not be specific to lwIP

examples/device/net_lwip_webserver/src/main.c

@@ -99,7 +99,7 @@ static err_t linkoutput_fn(struct netif *netif, struct pbuf *p)
     /* if the network driver can accept another packet, we make it happen */
     if (tud_network_can_xmit())
     {
-      tud_network_xmit(p);
+      tud_network_xmit(p, 0 /* unused for this example */);
       return ERR_OK;
     }
 
@@ -152,17 +152,49 @@ bool dns_query_proc(const char *name, ip_addr_t *addr)
   return false;
 }
 
-bool tud_network_recv_cb(struct pbuf *p)
+bool tud_network_recv_cb(const uint8_t *src, uint16_t size)
 {
   /* this shouldn't happen, but if we get another packet before 
   parsing the previous, we must signal our inability to accept it */
   if (received_frame) return false;
 
-  /* store away the pointer for service_traffic() to later handle */
-  received_frame = p;
+  if (size)
+  {
+    struct pbuf *p = pbuf_alloc(PBUF_RAW, size, PBUF_POOL);
+
+    if (p)
+    {
+      /* pbuf_alloc() has already initialized struct; all we need to do is copy the data */
+      memcpy(p->payload, src, size);
+
+      /* store away the pointer for service_traffic() to later handle */
+      received_frame = p;
+    }
+  }
+
   return true;
 }
 
+uint16_t tud_network_xmit_cb(uint8_t *dst, void *ref, uint16_t arg)
+{
+  struct pbuf *p = (struct pbuf *)ref;
+  struct pbuf *q;
+  uint16_t len = 0;
+
+  (void)arg; /* unused for this example */
+
+  /* traverse the "pbuf chain"; see ./lwip/src/core/pbuf.c for more info */
+  for(q = p; q != NULL; q = q->next)
+  {
+    memcpy(dst, (char *)q->payload, q->len);
+    dst += q->len;
+    len += q->len;
+    if (q->len == q->tot_len) break;
+  }
+
+  return len;
+}
+
 static void service_traffic(void)
 {
   /* handle any packet received by tud_network_recv_cb() */