Fixing (potentially) a buffer underflow in key_press_cb

Basically the inputs are goofy

cowterm.c

@@ -304,6 +304,10 @@ static void draw_char(Display *display, Drawable d, int x, int y) {
   if (x < 0 || x >= term_cols || y < 0 || y >= term_rows)
     return;
 
+  char c = terminal_buffer[y][x];
+  if (c < 32 || c > 126) // Only allow printable ASCII characters
+    return;
+
   unsigned long fg = color_buffer[y][x];
   unsigned long bg = bg_color_buffer[y][x];
   int attr = attr_buffer[y][x];
@@ -328,7 +332,7 @@ static void draw_char(Display *display, Drawable d, int x, int y) {
 
   XSetForeground(display, gc, fg);
 
-  char c[2] = {terminal_buffer[y][x], '\0'};
+  char str[2] = {c, '\0'};
   XFontStruct *font = regular_font;
 
   if (attr & ATTR_BOLD)
@@ -337,7 +341,8 @@ static void draw_char(Display *display, Drawable d, int x, int y) {
     font = italic_font;
 
   XSetFont(display, gc, font->fid);
-  XDrawString(display, d, gc, x * CHAR_WIDTH, (y + 1) * CHAR_HEIGHT - 4, c, 1);
+  XDrawString(display, d, gc, x * CHAR_WIDTH, (y + 1) * CHAR_HEIGHT - 4, str,
+              1);
 }
 
 static void draw_terminal(Display *display, Window window) {
@@ -785,6 +790,46 @@ static void parse_ansi_code(const char *buf, int *idx, int max_len,
 
   switch (buf[*idx]) {
   case 'H': // Set cursor position
+    if (param_idx >= 2) {
+      cursor_y = params[0] - 1 < 0            ? 0
+                 : params[0] - 1 >= term_rows ? term_rows - 1
+                                              : params[0] - 1;
+      cursor_x = params[1] - 1 < 0            ? 0
+                 : params[1] - 1 >= term_cols ? term_cols - 1
+                                              : params[1] - 1;
+    } else {
+      cursor_x = cursor_y = 0;
+    }
+    break;
+  case 's': // Save cursor position
+    if (param_idx == 0) {
+      saved_cursor_x = cursor_x;
+      saved_cursor_y = cursor_y;
+    }
+    break;
+  case 'u': // Restore cursor position
+    if (param_idx == 0) {
+      cursor_x = saved_cursor_x;
+      cursor_y = saved_cursor_y;
+    }
+    break;
+  case 'h': // Set mode
+  case 'l': // Reset mode
+    if (param_idx >= 1) {
+      switch (params[0]) {
+      case 25: // Show/hide cursor
+        cursor_visible = (buf[*idx] == 'h');
+        needs_refresh = 1;
+        break;
+      case 12: // Start/stop blinking cursor
+        cursor_visible = 1;
+        needs_refresh = 1;
+        break;
+      default:
+        break;
+      }
+    }
+    break;
   case 'f': // Alternative set cursor position
     if (param_idx >= 2) {
       cursor_y = params[0] - 1 < 0            ? 0
@@ -1062,8 +1107,11 @@ static void key_press_cb(XKeyEvent *event, void *data) {
       write(*master, "\025", 1);
       return;
     }
-    char ctrl_char = '@' + (keysym & 0x1f);
+    if ((keysym & 0x1f) >= '@' && (keysym & 0x1f) <= '_') {
-    write(*master, &ctrl_char, 1);
+      char ctrl_char = '@' + (keysym & 0x1f);
+      write(*master, &ctrl_char, 1);
+      return;
+    }
     return;
   }
 
@@ -1071,10 +1119,6 @@ static void key_press_cb(XKeyEvent *event, void *data) {
     write(*master, "\r", 1); // Shell handles return
   } else if (keysym == XK_BackSpace) {
     write(*master, "\177", 1); // Shell handles backspace
-  } else if (cursor_y > 0) {
-    char seq[8];
-    snprintf(seq, sizeof(seq), "\033[A\033[%dC", term_cols);
-    write(*master, seq, strlen(seq));
   } else if (keysym == XK_Left) {
     if (cursor_x > 0) {
       write(*master, "\033[D", 3);
@@ -1098,6 +1142,8 @@ static void key_press_cb(XKeyEvent *event, void *data) {
   } else if (keysym == XK_Tab) {
     write(*master, "\t", 1); // Shell handles autocomplete
   } else if (len > 0) {
+    if (len > (int)sizeof(buf))
+      len = sizeof(buf);
     write(*master, buf, len);
     if (cursor_x >= term_cols - 1) {
       write(*master, "\r\n", 2);
@@ -1236,8 +1282,9 @@ int main(void) {
         needs_refresh = 1;
         break;
       case KeyPress:
-        if (!(ev.xkey.state & ControlMask) && ev.xkey.keycode < 128)
+        if (ev.xkey.keycode < 128) {
           key_press_cb(&ev.xkey, &master);
+        }
         break;
       case Expose:
         needs_refresh = 1;