From 2d3928ed819862690becf015be560439a0b053c2 Mon Sep 17 00:00:00 2001
From: IFAKA <99131130+IFAKA@users.noreply.github.com>
Date: Fri, 19 Dec 2025 13:27:08 +0100
Subject: [PATCH] Validate file handle when reading progress.bin (#66)

## Problem
Reading progress.bin used `SD.exists()` then `SD.open()` without
checking if open succeeded. Race conditions or SD errors could cause
file handle to be invalid.

## Fix
- Removed redundant `SD.exists()` check
- Check if file opened successfully before reading
- Verify correct number of bytes were read

## Testing
- Builds successfully with `pio run`
- Affects: `src/activities/reader/EpubReaderActivity.cpp`
---
 src/activities/reader/EpubReaderActivity.cpp | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/src/activities/reader/EpubReaderActivity.cpp b/src/activities/reader/EpubReaderActivity.cpp
index 3bae96d..dd6dd04 100644
--- a/src/activities/reader/EpubReaderActivity.cpp
+++ b/src/activities/reader/EpubReaderActivity.cpp
@@ -33,13 +33,14 @@ void EpubReaderActivity::onEnter() {
 
   epub->setupCacheDir();
 
-  if (SD.exists((epub->getCachePath() + "/progress.bin").c_str())) {
-    File f = SD.open((epub->getCachePath() + "/progress.bin").c_str());
+  File f = SD.open((epub->getCachePath() + "/progress.bin").c_str());
+  if (f) {
     uint8_t data[4];
-    f.read(data, 4);
-    currentSpineIndex = data[0] + (data[1] << 8);
-    nextPageNumber = data[2] + (data[3] << 8);
-    Serial.printf("[%lu] [ERS] Loaded cache: %d, %d\n", millis(), currentSpineIndex, nextPageNumber);
+    if (f.read(data, 4) == 4) {
+      currentSpineIndex = data[0] + (data[1] << 8);
+      nextPageNumber = data[2] + (data[3] << 8);
+      Serial.printf("[%lu] [ERS] Loaded cache: %d, %d\n", millis(), currentSpineIndex, nextPageNumber);
+    }
     f.close();
   }