Fresh

Fresh is a RAM-first document database for ESP32 with owned, pluggable storage.

Fresh keeps small document collections and append-style logs in RAM while a background task persists them through a selected ESP-IDF storage backend.

Features

• RAM-first create, update, delete, and append operations.
• General JSON document models and append-style stream models.
• Owned LittleFS, SDSPI, SDMMC, eMMC, and custom storage backends.
• Application-file access through db.storage().
• Destructive whole-volume formatting through db.format().
• Background persistence, forced sync, streaming backup, and restore.
• FreshResult error handling without exceptions.
• FreeRTOS mutex protection and explicit shutdown behavior.

Install

PlatformIO

[env:esp32dev]platform = espressif32
board = esp32dev
framework = arduino
lib_deps =
https://github.com/ZekStack/fresh.git
bblanchon/ArduinoJson@>=7.0.0
build_flags =
-std=gnu++20
build_unflags =
-std=gnu++11

Arduino IDE

Fresh is not published to Arduino Library Manager yet. Download the repository ZIP or clone it into:

Arduino/libraries/Fresh

Quick start

#include<Arduino.h>
#include<Fresh.h>
Fresh db;
voidsetup() {
Serial.begin(115200);
FreshInitResult initialized = db.init("/fresh_app");
if (!initialized) {
Serial.println(initialized.message.c_str());
return;
}
FreshModelResult usersResult = db.createModel("User");
if (!usersResult && usersResult.status != FreshStatus::ModelExists) {
Serial.println(usersResult.message.c_str());
return;
}
FreshModel users = db.model("User");
JsonDocument user;
user["name"] = "Panna";
user["age"] = 19;
FreshResult created = users.create(user);
if (!created) {
Serial.println(created.message.c_str());
return;
}
FreshResult found = users.findById(user["_id"].as<constchar*>());
if (found) {
serializeJson(found.doc, Serial);
Serial.println();
}
}
voidloop() {
delay(1000);
}

The convenience overload above creates a default FreshLittleFSStorage.

Explicit storage

FreshConfig contains database settings only. Construct storage independently and pass it to init():

FreshConfig config;
config.syncIntervalMS = 5000;
FreshLittleFSConfig storageConfig;
storageConfig.partitionLabel = "spiffs";
storageConfig.mountPath = "/littlefs";
storageConfig.maxOpenFiles = 12;
storageConfig.formatOnMountFailure = false;
FreshInitResult initialized = db.init(
"/fresh_app",
config,
FreshLittleFSStorage(storageConfig)
);

Fresh owns the backend after successful initialization. A named backend must be moved:

FreshLittleFSStorage storage(storageConfig);
db.init("/fresh_app", config, std::move(storage));

Supported built-in backends:

• FreshLittleFSStorage
• FreshSDStorage with SDSPI
• FreshSDStorage with SDMMC
• FreshEMMCStorage

Custom classes can derive from FreshStorage.

Application files

Database and application files can share the selected backend without a separate filesystem wrapper:

FreshResult directory = db.storage().ensureDirectory("/backups");
constuint8_t marker[] = {1, 2, 3, 4};
FreshResult written = db.storage().writeFile(
"/backups/marker.bin",
marker,
sizeof(marker)
);
bool exists = db.storage().exists("/backups/marker.bin");

For streaming:

FreshFile file;
FreshResult opened = db.storage().open(
"/backups/system.fresh",
FreshOpenMode::Write,
file
);
if (!opened) return;
file.write(buffer, length);
file.syncAndClose();

The configured database root is protected from application storage operations. Open application files cause deinit() to return FreshStatus::Busy until they are closed.

Fresh uses ESP-IDF filesystem and media drivers directly. It does not include or synchronize Arduino's global LittleFS, SD, or SD_MMC objects.

Formatting storage

Caution

db.format() formats the complete configured storage volume. It deletes the Fresh database, application files, and unrelated files stored on the same filesystem.

FreshResult formatted = db.format();
if (!formatted) {
Serial.println(formatted.message.c_str());
return;
}
// The same Fresh instance is initialized again as an empty database.
db.createModel("settings");

Formatting stops background work, closes and invalidates all tracked files, invalidates existing model handles, writes an empty durable manifest, and restarts the sync task. Use dropAllModels() when files outside the database must be preserved. See Formatting storage for the custom-backend contract and failure behavior.

Persistence behavior

Important

A successful public mutation means the change was accepted in RAM. It does not necessarily mean the change has reached storage.

Operation	RAM updated	Storage updated before return
create() / update() / delete() / append()	yes	no
flush()	yes	captured journal operations
forceSyncAsync()	yes	no
forceSync()	yes	yes, when successful
format()	reset	empty database manifest
deinit({ .sync = true })	yes	yes, when successful

Additional lifecycle rules:

• Background sync captures dirty state under a short database lock and performs storage I/O outside that lock.
• forceSync() performs a blocking forced checkpoint in the caller context.
• format() performs a destructive synchronous lifecycle transition without a final sync.
• deinit() performs a final sync by default and waits for the sync task to exit.
• A timed-out deinit() may be called again to finish shutdown.
• FreshFile operations are mutex-protected.
• Callbacks are notifications; schedule blocking database or storage work on another task.

Examples

Example	Description
Basic	Minimal model and document usage.
Crud	General-model CRUD operations.
StreamModel	Append and retrieve stream records.
BackupStream	Streaming backup lifecycle.
LittleFSStorage	Explicit LittleFS backend and application files.
SDSPIStorage	SD card over SPI.
SDMMCStorage	SD card over SDMMC, including Waveshare ESP32-P4 pins and power setup.
EMMCStorage	Dedicated eMMC backend.
SameFilesystemBackup	Write a backup archive through db.storage().
CustomStorage	Owned custom backend over an external medium.
StorageLifecycleRegressionTest	Storage ownership, path protection, and shutdown.
StorageFormatRegressionTest	Whole-volume format lifecycle and failure behavior.
StorageFailureRegressionTest	Inject file and backend failures.
HardeningRegressionTest	Mutation and shutdown hardening.

Regression sketches are compiled in CI but require manual execution on hardware.

Documentation

• Getting started
• Configuration
• Storage
• Formatting storage
• API reference
• Examples
• Migrating to 0.2.0
• 0.2.0 release notes
• Storage implementation progress
• Troubleshooting
• Release hardening

Compatibility

Item	Support
Framework	Arduino as an ESP-IDF component / Arduino ESP32
Language	C++20
Storage drivers	ESP-IDF LittleFS, SDSPI, SDMMC, eMMC, custom
Persistence encoding	ArduinoJson MessagePack
PSRAM	Used for eligible internal allocations when available
Exceptions	Not used by the Fresh API
Status	0.2.0 pre-release

Limitations

Fresh is not intended for large datasets, high-frequency telemetry, SQL-style queries, multi-device concurrency, or data that must be durable after every public mutation.

Automatic SD hot-swap recovery, automatic remount, and multiple simultaneously managed volumes are not part of 0.2.0-rc.1.

License

MIT — see LICENSE.md.

ZekStack

Fresh is part of the ZekStack ESP32 library stack.