Use strnlen() for some string width calculations

Specifically in these functions:
  Action_setScreenTab()
  TextMeterMode_draw()
  LEDMeterMode_draw()
  RowField_keyAt()
  drawTab() (ScreenManager.c)

The strnlen() function does not calculate true display widths of the
Unicode strings, but at least it works with ASCII strings. The function
that can calculate display widths of Unicode strings is yet to be
implemented.

The goal of this commit is to prevent potential arithmetic overflows
when calculating string widths and to allow a safe downcast from
'size_t' to 'int' type. This fixes some of the '-Wshorten-64-to-32'
warnings produced by Clang (see issue #1673) as a result.

Signed-off-by: Kang-Che Sung <[email protected]>

Author: Explorer09

Action.c

@@ -402,19 +402,27 @@ static Htop_Reaction actionPrevScreen(State* st) {
 
 Htop_Reaction Action_setScreenTab(State* st, int x) {
    Settings* settings = st->host->settings;
-   int s = SCREEN_TAB_MARGIN_LEFT;
+
+   if (x < SCREEN_TAB_MARGIN_LEFT) {
+      return 0;
+   }
+
+   int rem = x - SCREEN_TAB_MARGIN_LEFT;
    for (unsigned int i = 0; i < settings->nScreens; i++) {
-      if (x < s) {
-         return 0;
-      }
       const char* tab = settings->screens[i]->heading;
-      int len = strlen(tab);
-      if (x < s + len + 2) {
+      int width = rem >= 2 ? (int)strnlen(tab, (unsigned int)(rem - 2 + 1)) : 0;
+      if (rem - 2 < width) {
          settings->ssIndex = i;
          setActiveScreen(settings, st, i);
          return HTOP_UPDATE_PANELHDR | HTOP_REFRESH | HTOP_REDRAW_BAR;
       }
-      s += len + 2 + SCREEN_TAB_COLUMN_GAP;
+
+      rem = rem - 2 - width;
+      if (rem < SCREEN_TAB_COLUMN_GAP) {
+         return 0;
+      }
+
+      rem -= SCREEN_TAB_COLUMN_GAP;
    }
    return 0;
 }

Meter.c

@@ -60,12 +60,12 @@ static void TextMeterMode_draw(Meter* this, int x, int y, int w) {
    }
    attrset(CRT_colors[RESET_COLOR]);
 
-   int captionLen = strlen(caption);
-   w -= captionLen;
-   if (w < 1) {
+   int captionWidth = w >= 1 ? (int)strnlen(caption, w) : 0;
+   if (w <= captionWidth) {
       return;
    }
-   x += captionLen;
+   w -= captionWidth;
+   x += captionWidth;
 
    RichString_begin(out);
    Meter_displayBuffer(this, &out);
@@ -340,11 +340,11 @@ static void LEDMeterMode_draw(Meter* this, int x, int y, int w) {
       mvaddnstr(yText, x, caption, w);
    }
 
-   int captionLen = strlen(caption);
-   if (w <= captionLen) {
+   int captionWidth = w >= 1 ? (int)strnlen(caption, w) : 0;
+   if (w <= captionWidth) {
       goto end;
    }
-   int xx = x + captionLen;
+   int xx = x + captionWidth;
 
 #ifdef HAVE_LIBNCURSESW
    if (CRT_utf8)

Row.c

@@ -179,13 +179,13 @@ const char* RowField_alignedTitle(const Settings* settings, RowField field) {
 RowField RowField_keyAt(const Settings* settings, int at) {
    const RowField* fields = (const RowField*) settings->ss->fields;
    RowField field;
-   int x = 0;
+   int rem = at;
    for (int i = 0; (field = fields[i]); i++) {
-      int len = strlen(RowField_alignedTitle(settings, field));
-      if (at >= x && at <= x + len) {
+      int len = rem > 0 ? (int)strnlen(RowField_alignedTitle(settings, field), rem) : 0;
+      if (rem <= len) {
          return field;
       }
-      x += len;
+      rem -= len;
    }
    return COMM;
 }

ScreenManager.c

@@ -166,11 +166,10 @@ static inline bool drawTab(const int* y, int* x, int l, const char* name, bool c
    (*x)++;
    if (*x >= l)
       return false;
-   int nameLen = strlen(name);
-   int n = MINIMUM(l - *x, nameLen);
+   int nameWidth = (int)strnlen(name, l - *x);
    attrset(CRT_colors[cur ? SCREENS_CUR_TEXT : SCREENS_OTH_TEXT]);
-   mvaddnstr(*y, *x, name, n);
-   *x += n;
+   mvaddnstr(*y, *x, name, nameWidth);
+   *x += nameWidth;
    if (*x >= l)
       return false;
    attrset(CRT_colors[cur ? SCREENS_CUR_BORDER : SCREENS_OTH_BORDER]);