From da48a52d7a8854363946fe0c05f02ec029c852c5 Mon Sep 17 00:00:00 2001
From: Eli Lipsitz <552502+elipsitz@users.noreply.github.com>
Date: Tue, 6 Dec 2022 13:56:49 -0600
Subject: [PATCH] Fix File::readString to work with binary data (#8742)

Previously, File::readString used a C-style string as an intermediate
buffer via the String += operator. This treats a NUL byte as a
terminator, making this function work incorrectly if the File contains
binary data.

This commit switches the function to use String::concat, which doesn't
treat NUL bytes any differently (and is a bit faster, because it doesn't
need to use strlen).
---
 cores/esp8266/FS.cpp | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/cores/esp8266/FS.cpp b/cores/esp8266/FS.cpp
index d9e4209c0..edfc1f8b4 100644
--- a/cores/esp8266/FS.cpp
+++ b/cores/esp8266/FS.cpp
@@ -173,18 +173,15 @@ File File::openNextFile() {
     return _fakeDir->openFile("r");
 }
 
-String File::readString()
-{
+String File::readString() {
     String ret;
     ret.reserve(size() - position());
-    char temp[256+1];
-    int countRead = readBytes(temp, sizeof(temp)-1);
-    while (countRead > 0)
-    {
-        temp[countRead] = 0;
-        ret += temp;
-        countRead = readBytes(temp, sizeof(temp)-1);
-    }
+    uint8_t temp[256];
+    int countRead;
+    do {
+        countRead = read(temp, sizeof(temp));
+        ret.concat((const char*)temp, countRead);
+    } while (countRead > 0);
     return ret;
 }