Remove temporary buffer in ConfigFile.ino

[bblanchon]

Hi,

Thank you guys for maintaining this critical piece of software that is at the heart of so many projects 👍

This PR simplifies the ConfigFile.ino example by removing the temporary buffer and passing the File directly to deserializeJson().

When reading from a Stream, using a temporary buffer is counterproductive because it complexifies the code and increases memory usage. It's also a source of confusion because it can create dangling pointers in the JsonDocument.
The only benefit of using a buffer is the reading speed, but I don't think speed is the focus in this example; if it were, it would use a buffer in saveConfig() too.

By the way, this example has been the origin of many issues in ArduinoJson's tracker:

• some of keys and values would be changed after opening a file bblanchon/ArduinoJson#1643
• LittleFS with ArduinoJSON bblanchon/ArduinoJson#1473
• i need help in arduinojson bblanchon/ArduinoJson#1461
• ESP32 SPIFFS load radio stations example cause WDT reboot.  bblanchon/ArduinoJson#1445
• Example ArduinoJson migration from version 5 to 6 bblanchon/ArduinoJson#1276
• Key and value is present but returns NULL bblanchon/ArduinoJson#1273
• ESP32 - Overwriting config.json caused garbage input bblanchon/ArduinoJson#1222
• Parse config file from SPIFFS on a ESP32 bblanchon/ArduinoJson#1215
• DeserializationError of ESP32 SPIFFS json file returns error 'incompleteInput' bblanchon/ArduinoJson#1159
• QUESTION: Getting "null"s in return from fucntion returning DynamicJsonDocument bblanchon/ArduinoJson#1084
• How to check if json property is null  bblanchon/ArduinoJson#1049
• jSonDocument property: sometimes null, sometimes not! bblanchon/ArduinoJson#998
• serializeJson to SPIFFS seems not working for me after upgrade 5->6 bblanchon/ArduinoJson#958
• Garabage data at first name in JsonObject,for returned JsonObject from class member function bblanchon/ArduinoJson#785
• root is destroy in the void loop bblanchon/ArduinoJson#715
• How can I use a Struct to return JsonArray from a function ? bblanchon/ArduinoJson#610
• JSON gets corrupted when created from a temporary buffer bblanchon/ArduinoJson#593
• Can't load JsonObjects from SPIFFS  bblanchon/ArduinoJson#582
• Read settings once, parse file directly without "readBytes" and "buffer pointer" before bblanchon/ArduinoJson#570
• [Question] Is there any simple approach to update a field on parsed object and print back? bblanchon/ArduinoJson#553
• ESP8266 Object.printTo(SPIFFS_File) -> caused empty File bblanchon/ArduinoJson#514
• Problem with nested objects bblanchon/ArduinoJson#497
• Issue when trying to add an Object to a nested array bblanchon/ArduinoJson#493
• Parsing error with comment on json file bblanchon/ArduinoJson#421
• How to decode arrays in array? bblanchon/ArduinoJson#400
• parsing object mangles the input buffer and fails to parse, but parse returns true!  bblanchon/ArduinoJson#342
• Unable to deserialize. bblanchon/ArduinoJson#285

It seems that I've been doing the customer service for this example, so I wonder if it's wise to keep it considering there is a comparable example in ArduinoJson, with the differences that it uses SD instead of LittleFS and it shows how to apply best practices by copying the data in a struct.

Please let me know what you think.

Best regards,
Benoit

[d-a-v]

so I wonder if it's wise to keep it
Please let me know what you think.

The least we could do is to ask you to add a comment / link to your example from within this example.

[earlephilhower]

@bblanchon can you please merge this with current head? Your GH settings don't allow us to update this PR, and it;s out of date so can't merge.

[d-a-v]

I suggest to add this comment:

  #include <ArduinoJson.h>
  #include "FS.h"
  #include <LittleFS.h>

+ // more and possibly updated information can be found at:
+ // https://arduinojson.org/v6/example/config/

  bool loadConfig() {

[bblanchon]

I amended the commit to include the comments suggested by @d-a-v.