Added Preferences::begin overload to select non-default NVS partition

[bot1131357]

Preferences library currently works only with the default NVS partition named "nvs". I added an function overload for Preferences::begin to enable use of a separate NVS partition.

For example, if my NVS partition is named "app_data" and namespace "app", I can do the following:

Preferences prefs;
prefs.begin("app_data", "app", false); 

// example use
uint8_t tmp = prefs.getUChar("val1", 0xff);
prefs.putUChar("val1", 0x00);

First time contributing - let me know if I'm doing it wrong. Thanks.

[me-no-dev]

This could be done without the overload :)
How about you modify the existing function like this:

Preferences.h

bool begin(const char* name, bool readOnly = false, const char* partition_label=NULL);

Preferences.cpp

bool Preferences::begin(const char * name, bool readOnly, const char* partition_label){
    if(_started){
        return false;
    }
    _readOnly = readOnly;
    esp_err_t err = ESP_OK;
    if (partition_label != NULL) {
        err = nvs_flash_init_partition(partition_label);
        if (err) {
            log_e("nvs_flash_init_partition failed: %s", nvs_error(err));
            return false;
        }
        err = nvs_open_from_partition(partition_label, name, readOnly ? NVS_READONLY : NVS_READWRITE, &_handle);
    } else {
        err = nvs_open(name, readOnly?NVS_READONLY:NVS_READWRITE, &_handle);
    }
    if(err){
        log_e("nvs_open failed: %s", nvs_error(err));
        return false;
    }
    _started = true;
    return true;
}

[bot1131357]

Thanks for getting back to me!

I did consider doing this, but I wanted the arguments consistent with esp-idf:

esp_err_tnvs_open_from_partition(const char *part_name, const char *name, nvs_open_mode_topen_mode, nvs_handle_t *out_handle)

The parameter bool readOnly placed in between namespace and partition labels feels clunky to me.

Thoughts?

[me-no-dev]

This is Arduino and not IDF :) Partition name will be rarely used anyway

[bot1131357]

I have pushed the changes as per your suggestion. :)

Referring to my original example, now the partition selection becomes an optional argument to the existing Preference::begin function:

Preferences prefs;
prefs.begin("app", false, "app_data");  // additional parameter to specify non-default partition

[me-no-dev]

thanks :)

[bot1131357]

Thank you :)