input: discard a verbatim 0x0A or 0x00 byte, depending on the mode

This disallows entering a verbatim ^J (0x0A) when typing text or
search terms, and disallows a verbatim ^@ (0x00) when typing a
filename.  Nano beeps when the disallowed code is attempted.

This addresses https://savannah.gnu.org/bugs/?49897.

src/nano.c

@@ -1824,17 +1824,9 @@ void do_output(char *output, size_t output_len, bool allow_cntrls)
 #endif
 
     while (i < output_len) {
-	/* If control codes are allowed, encode a verbatim null as a newline,
-	 * and let a verbatim ^J create a whole new line. */
-	if (allow_cntrls) {
+	/* Encode an embedded NUL byte as 0x0A. */
 	if (output[i] == '\0')
 	    output[i] = '\n';
-	    else if (output[i] == '\n') {
-		do_enter();
-		i++;
-		continue;
-	    }
-	}
 
 	/* Get the next multibyte character. */
 	char_len = parse_mbchar(output + i, char_buf, NULL);

src/prompt.c

@@ -104,7 +104,7 @@ int do_statusbar_input(bool *ran_func, bool *finished)
     if ((have_shortcut || get_key_buffer_len() == 0) && kbinput != NULL) {
 	/* Inject all characters in the input buffer at once, filtering out
 	 * control characters. */
-	do_statusbar_output(kbinput, kbinput_len, TRUE, NULL);
+	do_statusbar_output(kbinput, kbinput_len, TRUE);
 
 	/* Empty the input buffer. */
 	kbinput_len = 0;
@@ -139,18 +139,7 @@ int do_statusbar_input(bool *ran_func, bool *finished)
 				s->scfunc == do_backspace))
 	    ;
 	else if (s->scfunc == do_verbatim_input) {
-	    bool got_newline = FALSE;
-		/* Whether we got a verbatim ^J. */
-
-	    do_statusbar_verbatim_input(&got_newline);
-
-	    /* If we got a verbatim ^J, remove it from the input buffer,
-	     * fake a press of Enter, and indicate that we're done. */
-	    if (got_newline) {
-		get_input(NULL, 1);
-		input = KEY_ENTER;
-		*finished = TRUE;
-	    }
+	    do_statusbar_verbatim_input();
 	} else if (s->scfunc == do_cut_text_void)
 	    do_statusbar_cut_text();
 	else if (s->scfunc == do_delete)
@@ -202,11 +191,10 @@ int do_statusbar_mouse(void)
 }
 #endif
 
-/* The user typed input_len multibyte characters.  Add them to the
- * statusbar prompt, setting got_newline to TRUE if we got a verbatim ^J,
- * and filtering out ASCII control characters if filtering is TRUE. */
+/* The user typed input_len multibyte characters.  Add them to the answer,
+ * filtering out ASCII control characters if filtering is TRUE. */
 void do_statusbar_output(int *the_input, size_t input_len,
-	bool filtering, bool *got_newline)
+	bool filtering)
 {
     char *output = charalloc(input_len + 1);
     char *char_buf = charalloc(mb_cur_max());
@@ -220,18 +208,9 @@ void do_statusbar_output(int *the_input, size_t input_len,
     i = 0;
 
     while (i < input_len) {
-	/* When not filtering, convert nulls and stop at a newline. */
-	if (!filtering) {
+	/* Encode any NUL byte as 0x0A. */
 	if (output[i] == '\0')
 	    output[i] = '\n';
-	    else if (output[i] == '\n') {
-		/* Put back the rest of the characters for reparsing,
-		 * indicate that we got a ^J and get out. */
-		unparse_kbinput(output + i, input_len - i);
-		*got_newline = TRUE;
-		return;
-	    }
-	}
 
 	/* Interpret the next multibyte character. */
 	char_len = parse_mbchar(output + i, char_buf, NULL);
@@ -369,19 +348,15 @@ void do_statusbar_prev_word(void)
 }
 #endif /* !NANO_TINY */
 
-/* Get verbatim input, setting got_newline to TRUE if we get a ^J as
- * part of the verbatim input. */
-void do_statusbar_verbatim_input(bool *got_newline)
+/* Get verbatim input and inject it into the answer, without filtering. */
+void do_statusbar_verbatim_input(void)
 {
     int *kbinput;
     size_t kbinput_len;
 
-    /* Read in all the verbatim characters. */
     kbinput = get_verbatim_kbinput(bottomwin, &kbinput_len);
 
-    /* Display all the verbatim characters at once, not filtering out
-     * control characters. */
-    do_statusbar_output(kbinput, kbinput_len, FALSE, got_newline);
+    do_statusbar_output(kbinput, kbinput_len, FALSE);
 }
 
 /* Return the zero-based column position of the cursor in the answer. */

src/proto.h

@@ -485,7 +485,7 @@ void do_output(char *output, size_t output_len, bool allow_cntrls);
 int do_statusbar_mouse(void);
 #endif
 void do_statusbar_output(int *the_input, size_t input_len,
-	bool filtering, bool *got_newline);
+	bool filtering);
 void do_statusbar_home(void);
 void do_statusbar_end(void);
 void do_statusbar_left(void);
@@ -497,7 +497,7 @@ void do_statusbar_cut_text(void);
 void do_statusbar_prev_word(void);
 void do_statusbar_next_word(void);
 #endif
-void do_statusbar_verbatim_input(bool *got_newline);
+void do_statusbar_verbatim_input(void);
 size_t statusbar_xplustabs(void);
 size_t get_statusbar_page_start(size_t start_col, size_t column);
 void reinit_statusbar_x(void);

src/winio.c

@@ -1442,9 +1442,15 @@ int *get_verbatim_kbinput(WINDOW *win, size_t *kbinput_len)
     if (!ISSET(REBIND_KEYPAD))
 	keypad(win, FALSE);
 
-    /* Read in a stream of characters and interpret it if possible. */
+    /* Read in one keycode, or one or two escapes. */
     retval = parse_verbatim_kbinput(win, kbinput_len);
 
+    /* If the code is invalid in the current mode, discard it. */
+    if ((*retval == '\n' && as_an_at) || (*retval == '\0' && !as_an_at)) {
+	*kbinput_len = 0;
+	beep();
+    }
+
     /* Turn flow control characters back on if necessary and turn the
      * keypad back on if necessary now that we're done. */
     if (ISSET(PRESERVE))