async saveRaw(buffer, targetPath) {
        const storagePath = path.join(this.storagePath, targetPath);
        const targetDir = path.dirname(storagePath);

        await fs.mkdirs(targetDir);
        await fs.writeFile(storagePath, buffer);

        // For local file system storage can use relative path so add a slash
        const fullUrl = (
            urlUtils.urlJoin('/', urlUtils.getSubdir(),
                this.staticFileURLPrefix,
                targetPath)
        ).replace(new RegExp(`\\${path.sep}`, 'g'), '/');

        return fullUrl;
    }
Saves a buffer in the targetPath
@param {Buffer} buffer is an instance of Buffer
@param {String} targetPath relative path NOT including storage path to which the buffer should be written
@returns {Promise<String>} a URL to retrieve the data