expo-secure-store/src/byteCounter.ts

Provides a way to encrypt and securely store key-value pairs locally on the device.

export const VALUE_BYTES_LIMIT = 2048;

// note this probably could be JS-engine dependent
// inspired by https://stackoverflow.com/a/39488643
export function byteCountOverLimit(value: string, limit: number): boolean {
  let bytes = 0;

  for (let i = 0; i < value.length; i++) {
    const codePoint = value.charCodeAt(i);

    // Lone surrogates cannot be passed to encodeURI
    if (codePoint >= 0xd800 && codePoint < 0xe000) {
      if (codePoint < 0xdc00 && i + 1 < value.length) {
        const next = value.charCodeAt(i + 1);

        if (next >= 0xdc00 && next < 0xe000) {
          bytes += 4;
          if (bytes > limit) {
            return true;
          }
          i++;
          continue;
        }
      }
    }

    bytes += codePoint < 0x80 ? 1 : codePoint < 0x800 ? 2 : 3;
    if (bytes > limit) {
      return true;
    }
  }

  return bytes > limit;
}