# src/layout.js

    // @flow

    import * as BufferLayout from 'buffer-layout';

    /**
     * Layout for a public key
     */
    export const publicKey = (property: string = 'publicKey'): Object => {
      return BufferLayout.blob(32, property);
    };

    /**
     * Layout for a 64bit unsigned value
     */
    export const uint64 = (property: string = 'uint64'): Object => {
      return BufferLayout.blob(8, property);
    };

    /**
     * Layout for a Rust String type
     */
    export const rustString = (property: string = 'string') => {
      const rsl = BufferLayout.struct(
        [
          BufferLayout.u32('length'),
          BufferLayout.u32('lengthPadding'),
          BufferLayout.blob(BufferLayout.offset(BufferLayout.u32(), -8), 'chars'),
        ],
        property,
      );
      const _decode = rsl.decode.bind(rsl);
      const _encode = rsl.encode.bind(rsl);

      rsl.decode = (buffer, offset) => {
        const data = _decode(buffer, offset);
        return data.chars.toString('utf8');
      };

      rsl.encode = (str, buffer, offset) => {
        const data = {
          chars: Buffer.from(str, 'utf8'),
        };
        return _encode(data, buffer, offset);
      };

      rsl.alloc = str => {
        return (
          BufferLayout.u32().span +
          BufferLayout.u32().span +
          Buffer.from(str, 'utf8').length
        );
      };

      return rsl;
    };

    export function getAlloc(type: Object, fields: Object): number {
      let alloc = 0;
      type.layout.fields.forEach(item => {
        if (item.span >= 0) {
          alloc += item.span;
        } else if (typeof item.alloc === 'function') {
          alloc += item.alloc(fields[item.property]);
        }
      });
      return alloc;
    }