ESP8266 SPIFFS textfile read returns weird characters - c++

Question

I'm trying to store some hex color palettes in the ESP8266's SPIFFS but when I try to retrieve them I get some weird chars. The code and the log output are below:
Code (ino file):
#include "FS.h" // https://github.com/esp8266/Arduino/
#include <JsonParser.h> // https://github.com/henrikekblad/ArduinoJson
#include <JsonGenerator.h> // https://github.com/henrikekblad/ArduinoJson
using namespace ArduinoJson;
void setup(void) {
Serial.begin(9600);
SPIFFS.format();
SPIFFS.begin();
writeTxtFile("/palettes/warm.json", "[\"ffffff\",\"ed1414\",\"f6f336\",\"ff7e15\"]");
writeTxtFile("/palettes/pastel.json", "[\"ffffff\",\"ff7b7b\",\"8fff70\",\"7878ff\"]");
readPalettes();
}
void loop(void) {
}
bool readPalettes(void) {
bool succeeded = true;
Dir dir = SPIFFS.openDir("/palettes");
while (dir.next()) {
File palette = dir.openFile("r");
if (!readFile(palette, loadPaletteJson)) succeeded = false;
palette.close();
yield();
}
return succeeded;
}
bool loadPaletteJson(char* json, String fileName) {
Serial.print(fileName);Serial.print(F(": "));Serial.println(json);
Parser::JsonParser<5> parser; // one palette is 1+4*1=5 tokens
Parser::JsonArray p = parser.parseArray(json);
if (p.success()) {
//Store the palettes in a vector using a specific structure
return true;
} else {
Serial.println(F("JSON parsing failed"));
}
return false;
}
bool readFile(File file, std::function<bool (char* json, String fileName)> callback) {
if (file) {
String fileName = file.name();
size_t fileSize = file.size();
Serial.print(F("Reading "));Serial.print(fileSize);Serial.print(F(" bytes from "));Serial.println(fileName);
if (fileSize <= 1024) {
char buf[fileSize];
file.readBytes(buf, fileSize);
return callback(buf, getBaseName(fileName));
} else {
Serial.println(F("file size is too large"));
}
} else {
Serial.println(F("file open failed"));
}
return false;
}
String getBaseName(String fileName) {
return fileName.substring(fileName.lastIndexOf('/') + 1, fileName.lastIndexOf('.'));
}
bool writeTxtFile(String path, String content) {
File file = SPIFFS.open(path, "w");
if (file) {
Serial.print(F("Writing content: "));Serial.print(content);Serial.print(F(" to: "));Serial.println(path);
file.print(content);
file.close();
return true;
} else {
Serial.print(F("file open failed: "));Serial.println(path);
}
return false;
}
Arduino's IDE console output:
Writing content: ["ffffff","ed1414","f6f336","ff7e15"] to: /palettes/warm.json
Writing content: ["ffffff","ff7b7b","8fff70","7878ff"] to: /palettes/pastel.json
Reading 37 bytes from /palettes/warm.json
warm: ["ffffff","ed1414","f6f336","ff7e15"]⸮?8⸮?tu #
JSON parsing failed
Reading 37 bytes from /palettes/pastel.json
pastel: ["ffffff","ff7b7b","8fff70","7878ff"]⸮?8⸮?tu #
JSON parsing failed
I don't understand why those chars (⸮?8⸮?tu #) are added to a limited sized buffer. I tried to replace my buffer (char buf[fileSize];) with a unique pointer like this: std::unique_ptr<char[]> buf(new char[fileSize]); (in the function readFile) using buf.get() in the next 2 statements but with the exact same result.
Am I missing something?
EDIT:
As #leetibbett mentioned below, I'm writing a String while trying to read bytes. here is the correction for readFile function:
bool readFile(File file, std::function<bool (char* json, String fileName)> callback) {
if (file) {
String fileName = file.name();
size_t fileSize = file.size();
Serial.print(F("Reading "));Serial.print(fileSize);Serial.print(F(" bytes from "));Serial.println(fileName);
if (fileSize <= 1024) {
String content = file.readStringUntil('\n');
return callback((char*)content.c_str(), getBaseName(fileName));
} else {
Serial.println(F("file size is too large"));
}
} else {
Serial.println(F("file open failed"));
}
return false;
}