From 7526309ccf38a6384d457f6f15c8f9eed5e9e76c Mon Sep 17 00:00:00 2001
From: Andrew <18502096+classicrocker883@users.noreply.github.com>
Date: Fri, 5 Sep 2025 23:00:28 -0400
Subject: [PATCH] =?UTF-8?q?=F0=9F=A7=91=E2=80=8D=F0=9F=92=BB=20Tweaks=20to?=
 =?UTF-8?q?=20our=20aging=20Arduino=20SdFat=20Library=20code=20(#28031)?=
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Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>
---
 Marlin/src/lcd/e3v2/proui/gcode_preview.cpp | 17 ++++++++++------
 Marlin/src/sd/SdBaseFile.cpp                | 22 ++++++++++++---------
 2 files changed, 24 insertions(+), 15 deletions(-)

diff --git a/Marlin/src/lcd/e3v2/proui/gcode_preview.cpp b/Marlin/src/lcd/e3v2/proui/gcode_preview.cpp
index 045615f3c2..9ad098f149 100644
--- a/Marlin/src/lcd/e3v2/proui/gcode_preview.cpp
+++ b/Marlin/src/lcd/e3v2/proui/gcode_preview.cpp
@@ -83,7 +83,7 @@ fileprop_t fileprop;
 void getValue(const char * const buf, PGM_P const key, float &value) {
   if (value != 0.0f) return;
 
-  char *posptr = strstr_P(buf, key);
+  const char *posptr = strstr_P(buf, key);
   if (posptr == nullptr) return;
 
   char num[10] = "";
@@ -101,8 +101,9 @@ void getValue(const char * const buf, PGM_P const key, float &value) {
 
 bool Preview::hasPreview() {
   const char * const tbstart = PSTR("; thumbnail begin " STRINGIFY(THUMBWIDTH) "x" STRINGIFY(THUMBHEIGHT));
-  char *posptr = nullptr;
+  const char *posptr = nullptr;
   uint32_t indx = 0;
+  uint32_t prev_indx = 0;
   float tmp = 0;
 
   fileprop.clear();
@@ -114,7 +115,7 @@ bool Preview::hasPreview() {
   uint8_t nbyte = 1;
   while (!fileprop.thumbstart && nbyte > 0 && indx < 4 * sizeof(buf)) {
     nbyte = card.read(buf, sizeof(buf) - 1);
-    if (nbyte > 0) {
+    if (nbyte >= 0) {
       buf[nbyte] = '\0';
       getValue(buf, PSTR(";TIME:"), fileprop.time);
       getValue(buf, PSTR(";Filament used:"), fileprop.filament);
@@ -132,13 +133,17 @@ bool Preview::hasPreview() {
       fileprop.height -= tmp;
       posptr = strstr_P(buf, tbstart);
       if (posptr != nullptr) {
-        fileprop.thumbstart = indx + (posptr - &buf[0]);
+        fileprop.thumbstart = indx + (posptr - buf);
       }
       else {
         indx += _MAX(10, nbyte - (signed)strlen_P(tbstart));
+        if (indx <= prev_indx) break;
+        prev_indx = indx;
         card.setIndex(indx);
       }
     }
+    else
+      break;
   }
 
   if (!fileprop.thumbstart) {
@@ -190,7 +195,7 @@ void Preview::drawFromSD() {
     return;
   }
 
-  MString<45> buf;
+  TString buf;
   dwinDrawRectangle(1, hmiData.colorBackground, 0, 0, DWIN_WIDTH, STATUS_Y - 1);
   if (fileprop.time) {
     buf.setf(F("Estimated time: %i:%02i"), (uint16_t)fileprop.time / 3600, ((uint16_t)fileprop.time % 3600) / 60);
@@ -210,7 +215,7 @@ void Preview::drawFromSD() {
   }
   DWINUI::drawButton(BTN_Print, 26, 290);
   DWINUI::drawButton(BTN_Cancel, 146, 290);
-  show();
+  if (fileprop.thumbsize) show();
   drawSelectHighlight(true, 290);
   dwinUpdateLCD();
 }
diff --git a/Marlin/src/sd/SdBaseFile.cpp b/Marlin/src/sd/SdBaseFile.cpp
index 3963043ca6..cc14ca9c29 100644
--- a/Marlin/src/sd/SdBaseFile.cpp
+++ b/Marlin/src/sd/SdBaseFile.cpp
@@ -255,10 +255,12 @@ bool SdBaseFile::exists(const char *name) {
  * If no data is read, fgets() returns zero for EOF or -1 if an error occurred.
  */
 int16_t SdBaseFile::fgets(char *str, int16_t num, char *delim) {
+  if (!str || num <= 1) return -1; // Ensure space for at least '\0'
+
   char ch;
   int16_t n = 0;
   int16_t r = -1;
-  while ((n + 1) < num && (r = read(&ch, 1)) == 1) {
+  while (n < num - 1 && (r = read(&ch, 1)) == 1) {
     // delete CR
     if (ch == '\r') continue;
     str[n++] = ch;
@@ -269,10 +271,7 @@ int16_t SdBaseFile::fgets(char *str, int16_t num, char *delim) {
       if (strchr(delim, ch)) break;
     }
   }
-  if (r < 0) {
-    // read error
-    return -1;
-  }
+  if (r < 0) return -1; // read error
   str[n] = '\0';
   return n;
 }
@@ -342,7 +341,9 @@ int8_t SdBaseFile::lsPrintNext(const uint8_t flags, const uint8_t indent) {
   uint8_t w = 0;
 
   while (1) {
-    if (read(&dir, sizeof(dir)) != sizeof(dir)) return 0;
+    const int16_t r = read(&dir, sizeof(dir));
+    if (r < 0) return -1;
+    if (r != sizeof(dir)) return 0;
     if (dir.name[0] == DIR_NAME_FREE) return 0;
 
     // skip deleted entry and entries for . and  ..
@@ -1277,7 +1278,8 @@ int SdBaseFile::peek() {
   filepos_t pos;
   getpos(&pos);
   int c = read();
-  if (c >= 0) setpos(&pos);
+  if (c < 0) return -1;
+  setpos(&pos);
   return c;
 }
 
@@ -1346,8 +1348,10 @@ bool SdBaseFile::printName() {
  * If an error occurs or end of file is reached -1 is returned.
  */
 int16_t SdBaseFile::read() {
-  uint8_t b;
-  return read(&b, 1) == 1 ? b : -1;
+  uint8_t b = 0;
+  const int16_t r = read(&b, 1);
+  if (r != 1) return -1;
+  return static_cast<int16_t>(b);
 }
 
 /**