Add set custom decode frame length function for C++ native only

Author: halx99

src/masio.cpp

@@ -293,6 +293,10 @@ io_service::io_service() : stopping_(false), thread_started_(false), interrupter
   ares_outstanding_work_ = 0;
 #endif
   ipsv_state_ = 0;
+
+  this->xdec_len_ = [](io_service *service, void *ptr, int len) {
+    return service->builtin_decode_frame_length(ptr, len);
+  };
 }
 
 io_service::~io_service() { stop_service(); }
@@ -383,6 +387,9 @@ void io_service::set_option(int option, ...)
     case MASIO_OPT_IO_EVENT_CALLBACK:
       this->on_event_ = std::move(*va_arg(ap, io_event_callback_t *));
       break;
+    case MASIO_OPT_DECODE_FRAME_LENGTH_FUNCTION:
+      this->xdec_len_ = std::move(*va_arg(ap, decode_frame_length_fn_t *));
+      break;
   }
 
   va_end(ap);
@@ -1174,7 +1181,7 @@ bool io_service::do_read(transport_ptr transport)
 #endif
       if (transport->receiving_pdu_elen_ == -1)
       { // decode length
-        int length = decode_frame_length(transport->buffer_, transport->offset_ + n);
+        int length = this->xdec_len_(this, transport->buffer_, transport->offset_ + n);
         if (length > 0)
         {
           transport->receiving_pdu_elen_ = length;
@@ -1556,7 +1563,7 @@ void io_service::handle_ares_work_finish(channel *)
 }
 #endif
 
-int io_service::decode_frame_length(void *ud, int n)
+int io_service::builtin_decode_frame_length(void *ud, int n)
 {
   if (options_.lfib.length_field_offset >= 0)
   {

src/masio.h

@@ -118,6 +118,7 @@ enum
   MASIO_OPT_LOG_FILE,
   MASIO_OPT_LFIB_PARAMS,
   MASIO_OPT_IO_EVENT_CALLBACK,
+  MASIO_OPT_DECODE_FRAME_LENGTH_FUNCTION, // Native C++ ONLY
 };
 
 typedef std::chrono::high_resolution_clock highp_clock_t;
@@ -309,6 +310,7 @@ class deadline_timer;
 
 typedef std::function<void(error_number)> send_pdu_callback_t;
 typedef std::function<void(event_ptr)> io_event_callback_t;
+typedef std::function<int(io_service *service, void *ptr, int len)> decode_frame_length_fn_t;
 
 class io_service
 {
@@ -448,7 +450,7 @@ class io_service
   void do_nonblocking_accept_completion(fd_set *fds_array, io_channel *);
 
   // -1 indicate failed, connection will be closed
-  int decode_frame_length(void *ptr, int len);
+  int builtin_decode_frame_length(void *ptr, int len);
 
 private:
   bool stopping_;
@@ -519,8 +521,12 @@ class io_service
       int max_frame_length    = SZ(10, M);
     } lfib;
     FILE *outf = nullptr;
+
   } options_;
 
+  // The decode frame length function
+  decode_frame_length_fn_t xdec_len_;
+
   // The resolve function
   resolv_fn_t xresolv_;