Arduino ESP32 Base64 decoding with MBedTLS

decode_base64_mbedtls.cpp

#include "mbedtls/base64.h"
#include "mbedtls/error.h"

size_t get_decoded_size(const char *base64_str_p) {
  if (base64_str_p == NULL) {
    return 0;
  }

  size_t pad_char_count = 0;
  size_t base64_str_len = strlen(base64_str_p);

  if ((base64_str_len < 4) || (base64_str_len % 4 != 0)) {
    return 0;
  }

  if (base64_str_p[base64_str_len - 1] == '=') {
    pad_char_count++;
  }

  if (base64_str_p[base64_str_len - 2] == '=') {
    pad_char_count++;
  }
  
  return (3 * (base64_str_len / 4)) - pad_char_count;
}

void setup() {
  const char *data_base64 = "RrDWIKA8fN1zroSWUaSLykGlLI3OeVSNkEz1HaUW5WcbUKCGxCOHZk9EEgGshY0ovbuRlnEPWE+WLZDVCq4k9b+ylckgvOx/PpiawezezdE6BgPjibaLRQ/PPnaMk+IuvTerX/f0ulICQWWZWIffA6GvYfrdjBk74cGwj+pIG3k=";
  size_t decoded_data_size = get_decoded_size(data_base64);

  uint8_t *decoded_data_buff = (uint8_t*)malloc(decoded_data_size);
  if (decoded_data_buff == NULL) {
    printf("Fail to allocate %zu bytes...\n", decoded_data_size);
    return;
  }
  
  size_t decoded_data_length = 0;
  int res = mbedtls_base64_decode(
    decoded_data_buff,
    decoded_data_size,
    &decoded_data_length,
    (const uint8_t*)data_base64,
    strlen(data_base64)
  );

  if (res != 0) {
    char err_buff_str[128];
    mbedtls_strerror(res, err_buff_str, sizeof(err_buff_str));
    printf("Failed decode data, error: %s\n", err_buff_str);
    free(decoded_data_buff);
    return;
  }

  printf("Data [%zu]: ", decoded_data_length);
  for (size_t i = 0; i < decoded_data_length; ++i) {
    printf("%02X ", decoded_data_buff[i]);
  }
  printf("\n");
  free(decoded_data_buff);
}

void loop() {
  delay(10);
}