Overflow detection, span-based signatures, flatten control flow

firmware/include/net.h

@@ -4,13 +4,14 @@
 #include <functional>
 #include <span>
 #include "span_writer.h"
+#include "msgpack.h"
 
 struct net_state {
     std::array<uint8_t, 6> mac;
     std::array<uint8_t, 4> ip;
 };
 
-using net_handler = std::function<size_t(std::span<const uint8_t> payload, span_writer &out)>;
+using net_handler = std::function<msgpack::result<size_t>(std::span<const uint8_t> payload, span_writer &out)>;
 
 bool net_init();
 const net_state& net_get_state();