OTA and base64 decoding

[embedded_systems]

I'm working on a custom OTA solution that encodes the .bin file using base64 and sends it to the esp32 in 1024 chunks using JSON. The server is working. Right now I get the entire image from the server, but I don't know how to decode the base64 code and save it to the OTA image.
The encoding table is encodeCharacterTable[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
The JSON looks similar to the following:

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{"off_set":1024,"image":"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA="}

I can get the image using:

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		cJSON * data_json = cJSON_GetObjectItem(root,"data");
		if(!data_json){
			ESP_LOGI(TAG, "Parse error, [%s]!\n", cJSON_GetErrorPtr());
			return;
		}
		data_json->valuestring;

Looking at the OTA example, I will need to do something like this:

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esp_err_t err;
/* update handle : set by esp_ota_begin(), must be freed via esp_ota_end() */
    esp_ota_handle_t update_handle = 0 ;
    const esp_partition_t *update_partition = NULL;

    ESP_LOGI(TAG, "Starting OTA example...");

    const esp_partition_t *configured = esp_ota_get_boot_partition();
    const esp_partition_t *running = esp_ota_get_running_partition();

    assert(configured == running); /* fresh from reset, should be running from configured boot partition */
    ESP_LOGI(TAG, "Running partition type %d subtype %d (offset 0x%08x)",
             configured->type, configured->subtype, configured->address);

update_partition = esp_ota_get_next_update_partition(NULL);
    ESP_LOGI(TAG, "Writing to partition subtype %d at offset 0x%x",
             update_partition->subtype, update_partition->address);
    assert(update_partition != NULL);

err = esp_ota_begin(update_partition, OTA_SIZE_UNKNOWN, &update_handle);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "esp_ota_begin failed, error=%d", err);
        task_fatal_error();
    }
    ESP_LOGI(TAG, "esp_ota_begin succeeded");
    
    
    while(1){
    	//Read Data from socket. Decode base64 data -> ota_write_data
    	err = esp_ota_write( update_handle, (const void *)ota_write_data, buff_len);
    	if (err != ESP_OK) {
                ESP_LOGE(TAG, "Error: esp_ota_write failed! err=0x%x", err);
                task_fatal_error();
            }
    }
    if (esp_ota_end(update_handle) != ESP_OK) {
        ESP_LOGE(TAG, "esp_ota_end failed!");
        task_fatal_error();
    }
    err = esp_ota_set_boot_partition(update_partition);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "esp_ota_set_boot_partition failed! err=0x%x", err);
        task_fatal_error();
    }
    ESP_LOGI(TAG, "Prepare to restart system!");
    esp_restart();

I'm not sure how to decode the data and put it in ota_write_data so it can be used in

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err = esp_ota_write( update_handle, (const void *)ota_write_data, buff_len);
    	if (err != ESP_OK) {
                ESP_LOGE(TAG, "Error: esp_ota_write failed! err=0x%x", err);
                task_fatal_error();
            }

[embedded_systems]

Got it working. Below I have the code for the base64 decode.

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static const char  table[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static const int   BASE64_INPUT_SIZE = 57;

char isbase64(char c)
{
	return c && strchr(table, c) != NULL;
}

inline char value(char c)
{
	const char *p = strchr(table, c);
	if(p) {
		return p-table;
	} else {
		return 0;
	}
}

int UnBase64(unsigned char *dest, const unsigned char *src, int srclen)
{
	*dest = 0;
	if(*src == 0)
	{
		return 0;
	}
	unsigned char *p = dest;
	do
	{

		char a = value(src[0]);
		char b = value(src[1]);
		char c = value(src[2]);
		char d = value(src[3]);
		*p++ = (a << 2) | (b >> 4);
		*p++ = (b << 4) | (c >> 2);
		*p++ = (c << 6) | d;
		if(!isbase64(src[1]))
		{
			p -= 2;
			break;
		}
		else if(!isbase64(src[2]))
		{
			p -= 2;
			break;
		}
		else if(!isbase64(src[3]))
		{
			p--;
			break;
		}
		src += 4;
		while(*src && (*src == 13 || *src == 10)) src++;
	}
	while(srclen-= 4);
	*p = 0;
	printf("Csomplete\n");
	return p-dest;
}

[WiFive]

I think there are also base64 functions in mbedtls, wpa_supplicant, and ROM.