Allow non-inserting prediction.

This may be useful for users who find prediction's activity right of
the cursor distracting.

Prediction underscoring is still a little weird sometimes, it replays
a history of known/unknown changes as acks come in from the server.

scripts/mosh.pl

@@ -65,6 +65,8 @@ my $server = 'mosh-server';
 
 my $predict = undef;
 
+my $overwrite = 0;
+
 my $bind_ip = undef;
 
 my $use_remote_ip = 'proxy';
@@ -97,6 +99,8 @@ qq{Usage: $0 [options] [--] [user@]host [command...]
 -n      --predict=never         never use local echo
         --predict=experimental  aggressively echo even when incorrect
 
+-o      --overwrite             prediction overwrites instead of inserting
+
 -4      --family=inet        use IPv4 only
 -6      --family=inet6       use IPv6 only
         --family=auto        autodetect network type for single-family hosts only
@@ -150,6 +154,7 @@ sub predict_check {
 GetOptions( 'client=s' => \$client,
 	    'server=s' => \$server,
 	    'predict=s' => \$predict,
+	    'overwrite|o!' => \$overwrite,
 	    'port=s' => \$port_request,
 	    'a' => sub { $predict = 'always' },
 	    'n' => sub { $predict = 'never' },
@@ -200,6 +205,9 @@ if (!$have_ipv6) {
   # Force IPv4.
   $family = "inet";
 }
+if ( $overwrite ) {
+    $ENV{ "MOSH_PREDICTION_OVERWRITE" } = "yes";
+}
 
 if ( defined $port_request ) {
   if ( $port_request =~ m{^(\d+)(:(\d+))?$} ) {

src/frontend/mosh-client.cc

@@ -175,6 +175,10 @@ int main( int argc, char *argv[] )
   char *predict_mode = getenv( "MOSH_PREDICTION_DISPLAY" );
   /* can be NULL */
 
+  /* Read prediction insertion preference */
+  char *predict_overwrite = getenv( "MOSH_PREDICTION_OVERWRITE" );
+  /* can be NULL */
+
   char *key = strdup( env_key );
   if ( key == NULL ) {
     perror( "strdup" );
@@ -191,7 +195,7 @@ int main( int argc, char *argv[] )
 
   bool success = false;
   try {
-    STMClient client( ip, desired_port, key, predict_mode, verbose );
+    STMClient client( ip, desired_port, key, predict_mode, verbose, predict_overwrite );
     client.init();
 
     try {

src/frontend/stmclient.h

@@ -84,7 +84,7 @@ private:
   void resume( void ); /* restore state after SIGCONT */
 
 public:
-  STMClient( const char *s_ip, const char *s_port, const char *s_key, const char *predict_mode, unsigned int s_verbose )
+  STMClient( const char *s_ip, const char *s_port, const char *s_key, const char *predict_mode, unsigned int s_verbose, const char *predict_overwrite )
     : ip( s_ip ? s_ip : "" ), port( s_port ? s_port : "" ),
     key( s_key ? s_key : "" ),
     escape_key( 0x1E ), escape_pass_key( '^' ), escape_pass_key2( '^' ),
@@ -117,6 +117,9 @@ public:
 	exit( 1 );
       }
     }
+    if ( predict_overwrite && !strcmp( predict_overwrite, "yes" ) ) {
+      overlays.get_prediction_engine().set_predict_overwrite( true );
+    } 
   }
 
   void init( void );

src/frontend/terminaloverlay.cc

@@ -698,32 +698,45 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb )
 	  cursor().col--;
 	  cursor().expire( local_frame_sent + 1, now );
 
-	  for ( int i = cursor().col; i < fb.ds.get_width(); i++ ) {
+	  if ( predict_overwrite ) {
-	    ConditionalOverlayCell &cell = the_row.overlay_cells[ i ];
+	    ConditionalOverlayCell &cell = the_row.overlay_cells[ cursor().col ];
-	    
 	    cell.reset_with_orig();
 	    cell.active = true;
 	    cell.tentative_until_epoch = prediction_epoch;
 	    cell.expire( local_frame_sent + 1, now );
-	    cell.original_contents.push_back( *fb.get_cell( cursor().row, i ) );
+	    const Cell orig_cell = *fb.get_cell();
+	    cell.original_contents.push_back( orig_cell );
+	    cell.replacement = orig_cell;
+	    cell.replacement.clear();
+	    cell.replacement.append(' ');
+	  } else {
+	    for ( int i = cursor().col; i < fb.ds.get_width(); i++ ) {
+	      ConditionalOverlayCell &cell = the_row.overlay_cells[ i ];
 
-	    if ( i + 2 < fb.ds.get_width() ) {
+	      cell.reset_with_orig();
-	      ConditionalOverlayCell &next_cell = the_row.overlay_cells[ i + 1 ];
+	      cell.active = true;
-	      const Cell *next_cell_actual = fb.get_cell( cursor().row, i + 1 );
+	      cell.tentative_until_epoch = prediction_epoch;
+	      cell.expire( local_frame_sent + 1, now );
+	      cell.original_contents.push_back( *fb.get_cell( cursor().row, i ) );
 	  
-	      if ( next_cell.active ) {
+	      if ( i + 2 < fb.ds.get_width() ) {
-		if ( next_cell.unknown ) {
+		ConditionalOverlayCell &next_cell = the_row.overlay_cells[ i + 1 ];
-		  cell.unknown = true;
+		const Cell *next_cell_actual = fb.get_cell( cursor().row, i + 1 );
+
+		if ( next_cell.active ) {
+		  if ( next_cell.unknown ) {
+		    cell.unknown = true;
+		  } else {
+		    cell.unknown = false;
+		    cell.replacement = next_cell.replacement;
+		  }
 		} else {
 		  cell.unknown = false;
-		  cell.replacement = next_cell.replacement;
+		  cell.replacement = *next_cell_actual;
 		}
 	      } else {
-		cell.unknown = false;
+		cell.unknown = true;
-		cell.replacement = *next_cell_actual;
 	      }
-	    } else {
-	      cell.unknown = true;
 	    }
 	  }
 	}
@@ -746,7 +759,8 @@ void PredictionEngine::new_user_byte( char the_byte, const Framebuffer &fb )
 	}
 
 	/* do the insert */
-	for ( int i = fb.ds.get_width() - 1; i > cursor().col; i-- ) {
+	int rightmost_column = predict_overwrite ? cursor().col + 1 : fb.ds.get_width() - 1;
+	for ( int i = rightmost_column; i > cursor().col; i-- ) {
 	  ConditionalOverlayCell &cell = the_row.overlay_cells[ i ];
 	  cell.reset_with_orig();
 	  cell.active = true;

src/frontend/terminaloverlay.h

@@ -262,6 +262,7 @@ namespace Overlay {
 
   private:
     DisplayPreference display_preference;
+    bool predict_overwrite;
 
     bool active( void ) const;
 
@@ -272,6 +273,7 @@ namespace Overlay {
 
   public:
     void set_display_preference( DisplayPreference s_pref ) { display_preference = s_pref; }
+    void set_predict_overwrite( bool overwrite ) { predict_overwrite = overwrite; }
 
     void apply( Framebuffer &fb ) const;
     void new_user_byte( char the_byte, const Framebuffer &fb );
@@ -302,7 +304,8 @@ namespace Overlay {
 			       last_quick_confirmation( 0 ),
 			       send_interval( 250 ),
 			       last_height( 0 ), last_width( 0 ),
-			       display_preference( Adaptive )
+			       display_preference( Adaptive ),
+			       predict_overwrite( false )
     {
     }
   };