Protocol changes to support server-side delayed echoing

networktransport.cpp

@@ -15,6 +15,7 @@ Transport<MyState, RemoteState>::Transport( MyState &initial_state, RemoteState
     sender( &connection, initial_state ),
     received_states( 1, TimestampedState<RemoteState>( timestamp(), 0, initial_remote ) ),
     last_receiver_state( initial_remote ),
+    sent_state_late_acked( 0 ),
     fragments(),
     verbose( false )
 {
@@ -28,6 +29,7 @@ Transport<MyState, RemoteState>::Transport( MyState &initial_state, RemoteState
     sender( &connection, initial_state ),
     received_states( 1, TimestampedState<RemoteState>( timestamp(), 0, initial_remote ) ),
     last_receiver_state( initial_remote ),
+    sent_state_late_acked( 0 ),
     fragments(),
     verbose( false )
 {
@@ -48,7 +50,10 @@ void Transport<MyState, RemoteState>::recv( void )
     }
 
     sender.process_acknowledgment_through( inst.ack_num() );
-    
+    if ( inst.late_ack_num() > sent_state_late_acked ) {
+      sent_state_late_acked = inst.late_ack_num();
+    }
+
     /* first, make sure we don't already have the new state */
     for ( typename list< TimestampedState<RemoteState> >::iterator i = received_states.begin();
 	  i != received_states.end();

networktransport.hpp

@@ -30,6 +30,7 @@ namespace Network {
     /* simple receiver */
     list< TimestampedState<RemoteState> > received_states;
     RemoteState last_receiver_state; /* the state we were in when user last queried state */
+    uint64_t sent_state_late_acked;
     FragmentAssembly fragments;
     bool verbose;
 
@@ -53,32 +54,35 @@ namespace Network {
     /* Shut down other side of connection. */
     /* Illegal to change current_state after this. */
     void start_shutdown( void ) { sender.start_shutdown(); }
-    bool shutdown_in_progress( void ) { return sender.get_shutdown_in_progress(); }
+    bool shutdown_in_progress( void ) const { return sender.get_shutdown_in_progress(); }
-    bool shutdown_acknowledged( void ) { return sender.get_shutdown_acknowledged(); }
+    bool shutdown_acknowledged( void ) const { return sender.get_shutdown_acknowledged(); }
-    bool shutdown_ack_timed_out( void ) { return sender.shutdown_ack_timed_out(); }
+    bool shutdown_ack_timed_out( void ) const { return sender.shutdown_ack_timed_out(); }
-    bool attached( void ) { return connection.get_attached(); }
+    bool attached( void ) const { return connection.get_attached(); }
 
     /* Other side has requested shutdown and we have sent one ACK */
-    bool counterparty_shutdown_ack_sent( void ) { return sender.get_counterparty_shutdown_acknowledged(); }
+    bool counterparty_shutdown_ack_sent( void ) const { return sender.get_counterparty_shutdown_acknowledged(); }
 
-    int port( void ) { return connection.port(); }
+    int port( void ) const { return connection.port(); }
-    string get_key( void ) { return connection.get_key(); }
+    string get_key( void ) const { return connection.get_key(); }
 
     MyState &get_current_state( void ) { return sender.get_current_state(); }
     void set_current_state( const MyState &x ) { sender.set_current_state( x ); }
 
-    uint64_t get_remote_state_num( void ) { return received_states.back().num; }
+    uint64_t get_remote_state_num( void ) const { return received_states.back().num; }
 
     const TimestampedState<RemoteState> & get_latest_remote_state( void ) const { return received_states.back(); }
 
-    int fd( void ) { return connection.fd(); }
+    int fd( void ) const { return connection.fd(); }
 
     void set_verbose( void ) { sender.set_verbose(); verbose = true; }
 
     void set_send_delay( int new_delay ) { sender.set_send_delay( new_delay ); }
 
-    uint64_t get_sent_state_acked( void ) { return sender.get_sent_state_acked(); }
+    uint64_t get_sent_state_acked( void ) const { return sender.get_sent_state_acked(); }
-    uint64_t get_sent_state_last( void ) { return sender.get_sent_state_last(); }
+    uint64_t get_sent_state_last( void ) const { return sender.get_sent_state_last(); }
+    uint64_t get_sent_state_late_acked( void ) const { return sent_state_late_acked; }
+
+    unsigned int send_interval( void ) const { return sender.send_interval(); }
   };
 }
 

stmclient.cpp

@@ -155,9 +155,12 @@ bool STMClient::process_network_input( void )
 {
   network->recv();
   
+  /* Now give hints to the overlays */
   overlays.get_notification_engine().server_heard( network->get_latest_remote_state().timestamp );
 
   overlays.get_prediction_engine().set_local_frame_acked( network->get_sent_state_acked() );
+  overlays.get_prediction_engine().set_send_interval( network->send_interval() );
+  overlays.get_prediction_engine().set_local_frame_late_acked( network->get_sent_state_late_acked() );
 
   return true;
 }

terminaloverlay.cpp

@@ -8,10 +8,10 @@
 
 using namespace Overlay;
 
-bool ConditionalOverlay::start_clock( uint64_t local_frame_acked, uint64_t now )
+bool ConditionalOverlay::start_clock( uint64_t local_frame_acked, uint64_t now, unsigned int send_interval )
 {
   if ( (local_frame_acked >= expiration_frame) && (expiration_time == uint64_t(-1)) ) {
-    expiration_time = now + 50;
+    expiration_time = now + 25 + 125 * send_interval / 100;
     return true;
   }
   return false;
@@ -53,7 +53,9 @@ void ConditionalOverlayCell::apply( Framebuffer &fb, uint64_t confirmed_epoch, i
   }
 }
 
-Validity ConditionalOverlayCell::get_validity( const Framebuffer &fb, int row, uint64_t current_frame, uint64_t now ) const
+Validity ConditionalOverlayCell::get_validity( const Framebuffer &fb, int row,
+					       uint64_t sent_frame, uint64_t early_ack, uint64_t late_ack,
+					       uint64_t now ) const
 {
   if ( !active ) {
     return Inactive;
@@ -67,7 +69,7 @@ Validity ConditionalOverlayCell::get_validity( const Framebuffer &fb, int row, u
   const Cell &current = *( fb.get_cell( row, col ) );
 
   /* see if it hasn't been updated yet */
-  if ( current_frame < expiration_frame ) {
+  if ( early_ack < expiration_frame ) {
     return Pending;
   }
 
@@ -92,14 +94,15 @@ Validity ConditionalOverlayCell::get_validity( const Framebuffer &fb, int row, u
 
   assert( expiration_time != uint64_t(-1) );
 
-  if ( now < expiration_time ) {
+  if ( (late_ack >= expiration_frame)
-    return Pending;
+       || ( (sent_frame <= early_ack) && (expiration_time >= now) ) ) {
+    return IncorrectOrExpired;
   }
 
-  return IncorrectOrExpired;
+  return Pending;
 }
 
-Validity ConditionalCursorMove::get_validity( const Framebuffer &fb, uint64_t current_frame, uint64_t now ) const
+Validity ConditionalCursorMove::get_validity( const Framebuffer &fb, uint64_t sent_frame, uint64_t early_ack, uint64_t late_ack, uint64_t now ) const
 {
   if ( !active ) {
     return Inactive;
@@ -112,7 +115,7 @@ Validity ConditionalCursorMove::get_validity( const Framebuffer &fb, uint64_t cu
     return IncorrectOrExpired;
   }
 
-  if ( current_frame < expiration_frame ) {
+  if ( early_ack < expiration_frame ) {
     return Pending;
   }
 
@@ -123,15 +126,12 @@ Validity ConditionalCursorMove::get_validity( const Framebuffer &fb, uint64_t cu
 
   assert( expiration_time != uint64_t(-1) );
 
-  if ( now < expiration_time ) {
+  if ( (late_ack >= expiration_frame)
-    return Pending;
+       || ( (sent_frame <= early_ack) && (expiration_time >= now) ) ) {
+    return IncorrectOrExpired;
   }
 
-  /*
+  return Pending;
-    fprintf( stderr, "Bad cursor in %d (I thought (%d,%d) vs actual (%d,%d)).\n", (int)current_frame,
-    row, col, fb.ds.get_cursor_row(), fb.ds.get_cursor_col() );
-  */
-  return IncorrectOrExpired;
 }
 
 void ConditionalCursorMove::apply( Framebuffer &fb, uint64_t confirmed_epoch ) const
@@ -349,6 +349,14 @@ void PredictionEngine::init_cursor( const Framebuffer &fb )
 					      fb.ds.get_cursor_row(),
 					      fb.ds.get_cursor_col(),
 					      prediction_epoch ) );
+
+    cursor().active = true;
+  } else if ( cursor().tentative_until_epoch != prediction_epoch ) {
+    cursors.push_back( ConditionalCursorMove( local_frame_sent + 1,
+					      cursor().row,
+					      cursor().col,
+					      prediction_epoch ) );
+
     cursor().active = true;
   }
 }
@@ -369,22 +377,13 @@ void PredictionEngine::cull( const Framebuffer &fb )
       continue;
     }
 
-    /* smash through "shell prompt" barrier if host has let us */
-    if ( fb.ds.get_cursor_row() == i->row_num ) {
-      if ( i->first_col != INT_MAX ) {
-	if ( fb.ds.get_cursor_col() < i->first_col ) {
-	  i->first_col = 0;
-	}
-      } else {
-	i->first_col = fb.ds.get_cursor_col();
-      }
-    }
-
     for ( auto j = i->overlay_cells.begin(); j != i->overlay_cells.end(); j++ ) {
-      if ( j->start_clock( local_frame_acked, now  ) ) {
+      if ( j->start_clock( local_frame_acked, now, send_interval ) ) {
 	last_scheduled_timeout = max( last_scheduled_timeout, j->expiration_time );
       }
-      switch ( j->get_validity( fb, i->row_num, local_frame_acked, now ) ) {
+      switch ( j->get_validity( fb, i->row_num,
+				local_frame_sent, local_frame_acked, local_frame_late_acked,
+				now ) ) {
       case IncorrectOrExpired:
 	if ( j->tentative( confirmed_epoch ) ) {
 
@@ -440,29 +439,23 @@ void PredictionEngine::cull( const Framebuffer &fb )
 
 	if ( j->display_time != uint64_t(-1) ) {
 	  if ( now - j->display_time < 75 ) {
-	    if ( flagging > 0 ) {
+	    if ( flag_score > -10 ) {
-	      flagging--;
+	      flag_score--;
 	    }
 	  }
 	}
 
 	/* no break */
       case CorrectNoCredit:
-	if ( i->first_col != INT_MAX ) {
-	  if ( j->col < i->first_col ) {
-	    i->first_col = 0;
-	  }
-	} else {
-	  i->first_col = j->col;
-	}
-
 	j->reset();
 
 	break;
       case Pending:
 	if ( j->display_time != uint64_t(-1) ) {
-	  if ( now - j->display_time >= 150 ) {
+	  if ( now - j->display_time > 150 ) {
-	    flagging = 10;
+	    if ( flag_score < 10 ) {
+	      flag_score++;
+	    }
 	  }
 	}
 	break;
@@ -474,15 +467,24 @@ void PredictionEngine::cull( const Framebuffer &fb )
     i = inext;
   }
 
+  /* control flagging with hysteresis */
+  if ( flag_score > 5 ) {
+    flagging = true;
+  } else if ( flag_score < -5 ) {
+    flagging = false;
+  }
+
   /* go through cursor predictions */
   for ( auto it = cursors.begin(); it != cursors.end(); it++ ) {
-    if ( it->start_clock( local_frame_acked, now ) ) {
+    if ( it->start_clock( local_frame_acked, now, send_interval ) ) {
       last_scheduled_timeout = max( last_scheduled_timeout, it->expiration_time );
     }
   }
 
   if ( !cursors.empty() ) {
-    if ( cursor().get_validity( fb, local_frame_acked, now ) == IncorrectOrExpired ) {
+    if ( cursor().get_validity( fb,
+				local_frame_sent, local_frame_acked, local_frame_late_acked,
+				now ) == IncorrectOrExpired ) {
       /*
       fprintf( stderr, "Sadly, we're predicting (%d,%d) vs. (%d,%d) [tau: %ld, expiration_time=%ld, now=%ld]\n",
 	       cursor().row, cursor().col,
@@ -497,7 +499,10 @@ void PredictionEngine::cull( const Framebuffer &fb )
     }
   }
 
-  cursors.remove_if( [&]( ConditionalCursorMove &x ) { return (x.get_validity( fb, local_frame_acked, now ) != Pending); } );
+  cursors.remove_if( [&]( const ConditionalCursorMove &x ) {
+      return (x.get_validity( fb,
+			      local_frame_sent, local_frame_acked, local_frame_late_acked,
+			      now ) != Pending); } );
 }
 
 ConditionalOverlayRow & PredictionEngine::get_or_make_row( int row_num, int num_cols )
@@ -554,9 +559,6 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb )
       if ( ch == 0x7f ) { /* backspace */
 	//	fprintf( stderr, "Backspace.\n" );
 	ConditionalOverlayRow &the_row = get_or_make_row( cursor().row, fb.ds.get_width() );
-	if ( cursor().col <= the_row.first_col ) {
-	  become_tentative();
-	}
 
 	if ( cursor().col > 0 ) {
 	  cursor().col--;
@@ -654,10 +656,12 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb )
 	*/
 
 	cursor().expire( local_frame_sent + 1 );
-	cursor().col++;
 
 	/* do we need to wrap? */
-	if ( cursor().col >= fb.ds.get_width() ) {
+	if ( cursor().col < fb.ds.get_width() - 1 ) {
+	  cursor().col++;
+	} else {
+	  become_tentative();
 	  newline_carriage_return( fb );
 	}
       }
@@ -681,10 +685,6 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb )
 	}
       } else if ( act->char_present && (act->ch == L'D') ) { /* left arrow */
 	init_cursor( fb );
-	ConditionalOverlayRow &the_row = get_or_make_row( cursor().row, fb.ds.get_width() );
-	if ( cursor().col <= the_row.first_col ) {
-	  become_tentative();	    
-	}
 	
 	if ( cursor().col > 0 ) {
 	  cursor().col--;
@@ -733,13 +733,6 @@ void PredictionEngine::become_tentative( void )
 {
   prediction_epoch++;
 
-  if ( !cursors.empty() ) {
-    cursors.push_back( ConditionalCursorMove( local_frame_sent + 1,
-					      cursor().row,
-					      cursor().col,
-					      prediction_epoch ) );
-    cursor().active = true;
-  }
   /*
   fprintf( stderr, "Now tentative in epoch %lu (confirmed=%lu)\n",
 	   prediction_epoch, confirmed_epoch );

terminaloverlay.hpp

@@ -38,7 +38,7 @@ namespace Overlay {
 
     bool tentative( uint64_t confirmed_epoch ) const { return tentative_until_epoch > confirmed_epoch; }
     void reset( void ) { expiration_frame = expiration_time = tentative_until_epoch = -1; active = false; }
-    bool start_clock( uint64_t local_frame_acked, uint64_t now );
+    bool start_clock( uint64_t local_frame_acked, uint64_t now, unsigned int send_interval );
     void expire( uint64_t s_exp ) { expiration_frame = s_exp; expiration_time = uint64_t(-1); }
   };
 
@@ -48,7 +48,7 @@ namespace Overlay {
 
     void apply( Framebuffer &fb, uint64_t confirmed_epoch ) const;
 
-    Validity get_validity( const Framebuffer &fb, uint64_t current_frame, uint64_t now ) const;
+    Validity get_validity( const Framebuffer &fb, uint64_t sent_frame, uint64_t early_ack, uint64_t late_ack, uint64_t now ) const;
 
     ConditionalCursorMove( uint64_t s_exp, int s_row, int s_col, uint64_t s_tentative )
       : ConditionalOverlay( s_exp, s_col, s_tentative ), row( s_row )
@@ -66,7 +66,7 @@ namespace Overlay {
 				       that match the original contents */
 
     void apply( Framebuffer &fb, uint64_t confirmed_epoch, int row, bool flag ) const;
-    Validity get_validity( const Framebuffer &fb, int row, uint64_t current_frame, uint64_t now ) const;
+    Validity get_validity( const Framebuffer &fb, int row, uint64_t sent_frame, uint64_t early_ack, uint64_t late_ack, uint64_t now ) const;
 
     ConditionalOverlayCell( uint64_t s_exp, int s_col, uint64_t s_tentative )
       : ConditionalOverlay( s_exp, s_col, s_tentative ),
@@ -93,13 +93,12 @@ namespace Overlay {
   class ConditionalOverlayRow {
   public:
     int row_num;
-    int first_col;
 
     vector<ConditionalOverlayCell> overlay_cells;
 
     void apply( Framebuffer &fb, uint64_t confirmed_epoch, bool flag ) const;
 
-    ConditionalOverlayRow( int s_row_num ) : row_num( s_row_num ), first_col( INT_MAX ), overlay_cells() {}
+    ConditionalOverlayRow( int s_row_num ) : row_num( s_row_num ), overlay_cells() {}
   };
 
   /* the various overlays */
@@ -130,7 +129,7 @@ namespace Overlay {
 
     list<ConditionalCursorMove> cursors;
 
-    uint64_t local_frame_sent, local_frame_acked;
+    uint64_t local_frame_sent, local_frame_acked, local_frame_late_acked;
 
     ConditionalOverlayRow & get_or_make_row( int row_num, int num_cols );
 
@@ -141,7 +140,8 @@ namespace Overlay {
 
     void newline_carriage_return( const Framebuffer &fb );
 
-    int flagging;
+    int flag_score;
+    bool flagging;
 
     ConditionalCursorMove & cursor( void ) { assert( !cursors.empty() ); return cursors.back(); }
 
@@ -151,6 +151,8 @@ namespace Overlay {
 
     uint64_t last_scheduled_timeout;
 
+    unsigned int send_interval;
+
   public:
     void apply( Framebuffer &fb ) const;
     void new_user_byte( char the_byte, const Framebuffer &fb );
@@ -162,11 +164,16 @@ namespace Overlay {
 
     void set_local_frame_sent( uint64_t x ) { local_frame_sent = x; }
     void set_local_frame_acked( uint64_t x ) { local_frame_acked = x; }
+    void set_local_frame_late_acked( uint64_t x ) { local_frame_late_acked = x; }
+
+    void set_send_interval( unsigned int x ) { send_interval = x; }
 
     PredictionEngine( void ) : last_byte( 0 ), parser(), overlays(), cursors(),
 			       local_frame_sent( 0 ), local_frame_acked( 0 ),
+			       local_frame_late_acked( 0 ),
 			       prediction_epoch( 1 ), confirmed_epoch( 0 ),
-			       flagging( 0 ), last_scheduled_timeout( 0 )
+			       flag_score( 0 ), flagging( false ), last_scheduled_timeout( 0 ),
+			       send_interval( 250 )
     {
     }
   };

transportfragment.cpp

@@ -124,6 +124,8 @@ vector<Fragment> Fragmenter::make_fragments( Instruction &inst, int MTU )
        || (inst.new_num() != last_instruction.new_num())
        || (inst.ack_num() != last_instruction.ack_num())
        || (inst.throwaway_num() != last_instruction.throwaway_num())
+       || (inst.late_ack_num() != last_instruction.late_ack_num())
+       || (inst.protocol_version() != last_instruction.protocol_version())
        || (last_MTU != MTU) ) {
     next_instruction_id++;
   }

transportfragment.hpp

@@ -70,7 +70,7 @@ namespace Network {
       last_instruction.set_new_num( -1 );
     }
     vector<Fragment> make_fragments( Instruction &inst, int MTU );
-    uint64_t last_ack_sent( void ) { return last_instruction.ack_num(); }
+    uint64_t last_ack_sent( void ) const { return last_instruction.ack_num(); }
   };
   
 }

transportinstruction.proto

@@ -9,6 +9,7 @@ message Instruction {
   optional uint64 new_num = 3;
   optional uint64 ack_num = 4;
   optional uint64 throwaway_num = 5;
+  optional uint64 late_ack_num = 7;
 
   optional bytes diff = 6;
 }

transportsender.cpp

@@ -21,13 +21,14 @@ TransportSender<MyState>::TransportSender( Connection *s_connection, MyState &in
     ack_num( 0 ),
     pending_data_ack( false ),
     ack_timestamp( 0 ),
+    ack_history(),
     SEND_MINDELAY( 15 )
 {
 }
 
 /* Try to send roughly two frames per RTT, bounded by limits on frame rate */
 template <class MyState>
-unsigned int TransportSender<MyState>::send_interval( void )
+unsigned int TransportSender<MyState>::send_interval( void ) const
 {
   int SEND_INTERVAL = lrint( ceil( connection->get_SRTT() / 2.0 ) );
   if ( SEND_INTERVAL < SEND_INTERVAL_MIN ) {
@@ -227,6 +228,7 @@ void TransportSender<MyState>::send_in_fragments( string diff, uint64_t new_num
   inst.set_new_num( new_num );
   inst.set_ack_num( ack_num );
   inst.set_throwaway_num( sent_states.front().num );
+  inst.set_late_ack_num( get_late_ack( now ) );
   inst.set_diff( diff );
 
   if ( new_num == uint64_t(-1) ) {
@@ -258,8 +260,8 @@ void TransportSender<MyState>::process_acknowledgment_through( uint64_t ack_num
   /* Ignore ack if we have culled the state it's acknowledging */
 
   if ( sent_states.end() != find_if( sent_states.begin(), sent_states.end(),
-				     [&]( TimestampedState<MyState> &x ) { return x.num == ack_num; } ) ) {
+				     [&]( const TimestampedState<MyState> &x ) { return x.num == ack_num; } ) ) {
-    sent_states.remove_if( [&]( TimestampedState<MyState> &x ) { return x.num < ack_num; } );
+    sent_states.remove_if( [&]( const TimestampedState<MyState> &x ) { return x.num < ack_num; } );
   }
 
   assert( !sent_states.empty() );
@@ -267,7 +269,7 @@ void TransportSender<MyState>::process_acknowledgment_through( uint64_t ack_num
 
 /* give up on getting acknowledgement for shutdown */
 template <class MyState>
-bool TransportSender<MyState>::shutdown_ack_timed_out( void )
+bool TransportSender<MyState>::shutdown_ack_timed_out( void ) const
 {
   return shutdown_tries >= SHUTDOWN_RETRIES;
 }
@@ -278,4 +280,17 @@ void TransportSender<MyState>::set_ack_num( uint64_t s_ack_num )
 {
   ack_num = s_ack_num;
   ack_timestamp = timestamp();
+  ack_history.push_back( make_pair( ack_num, ack_timestamp ) );
+}
+
+/* The "late" ack is for the input state that has had enough time on the host to have been echoed */
+template <class MyState>
+uint64_t TransportSender<MyState>::get_late_ack( uint64_t now )
+{
+  ack_history.remove_if( [&]( const pair<uint64_t, uint64_t> &x ) { return x.second < now - ECHO_TIMEOUT; } );
+  if ( !ack_history.empty() ) {
+    return ack_history.front().first - 1;
+  } else { /* every ack has gone past the echo timeout */
+    return ack_num;
+  }
 }

transportsender.hpp

@@ -24,9 +24,9 @@ namespace Network {
     static const int ACK_INTERVAL = 3000; /* ms between empty acks */
     static const int ACK_DELAY = 100; /* ms before delayed ack */
     static const int SHUTDOWN_RETRIES = 3; /* number of shutdown packets to send before giving up */
+    static const int ECHO_TIMEOUT = 50; /* for late ack */
 
     /* helper methods for tick() */
-    unsigned int send_interval( void );
     void update_assumed_receiver_state( void );
     void rationalize_states( void );
     void send_to_receiver( string diff );
@@ -62,6 +62,9 @@ namespace Network {
     bool pending_data_ack;
     uint64_t ack_timestamp;
 
+    list< pair<uint64_t, uint64_t> > ack_history;
+    uint64_t get_late_ack( uint64_t now ); /* calculate delayed "echo" acknowledgment */
+
     unsigned int SEND_MINDELAY; /* ms to collect all input */
 
   public:
@@ -92,16 +95,18 @@ namespace Network {
     void set_current_state( const MyState &x ) { assert( !shutdown_in_progress ); current_state = x; }
     void set_verbose( void ) { verbose = true; }
 
-    bool get_shutdown_in_progress( void ) { return shutdown_in_progress; }
+    bool get_shutdown_in_progress( void ) const { return shutdown_in_progress; }
-    bool get_shutdown_acknowledged( void ) { return sent_states.front().num == uint64_t(-1); }
+    bool get_shutdown_acknowledged( void ) const { return sent_states.front().num == uint64_t(-1); }
-    bool get_counterparty_shutdown_acknowledged( void ) { return fragmenter.last_ack_sent() == uint64_t(-1); }
+    bool get_counterparty_shutdown_acknowledged( void ) const { return fragmenter.last_ack_sent() == uint64_t(-1); }
-    uint64_t get_sent_state_acked( void ) { return sent_states.front().num; }
+    uint64_t get_sent_state_acked( void ) const { return sent_states.front().num; }
-    uint64_t get_sent_state_last( void ) { return sent_states.back().num; }
+    uint64_t get_sent_state_last( void ) const { return sent_states.back().num; }
 
-    bool shutdown_ack_timed_out( void );
+    bool shutdown_ack_timed_out( void ) const;
 
     void set_send_delay( int new_delay ) { SEND_MINDELAY = new_delay; }
 
+    unsigned int send_interval( void ) const;
+
     /* nonexistent methods to satisfy -Weffc++ */
     TransportSender( const TransportSender &x );
     TransportSender & operator=( const TransportSender &x );