Google Drive: Download File

const REQUEST_NUM_PER_FILE = 4; // ファイル 1 つにつき 4 回リクエストを行う

function main() {
    ////// == 工程コンフィグ・ワークフローデータの参照 / Config & Data Retrieving ==
    const auth = configs.getObject('conf_Auth');
    const fileIds = retrieveFileIds();

    const fileDef = configs.getObject('conf_FileData');
    let files = engine.findData( fileDef );
    if (files === null) {
        files = new java.util.ArrayList();
    }

    ////// == 演算 / Calculating ==
    if (fileIds.length * REQUEST_NUM_PER_FILE > httpClient.getRequestingLimit()) {
        throw new Error('Number of File IDs exceeds the limit.');
    }
    fileIds.forEach(fileId => {
        const {name, contentType} = getFileMetadata(auth, fileId);
        const content = getFile(auth, fileId);
        const qfile = new com.questetra.bpms.core.event.scripttask.NewQfile(
            name, contentType, content
        );
        files.add(qfile);
    });

    ////// == ワークフローデータへの代入 / Data Updating ==
    engine.setData(fileDef, files);
}

/**
 * config からファイル ID を読み出す
 * ファイル ID が設定されていない場合はエラー
 * @returns {Array<String>} ファイル ID の配列
 */
const retrieveFileIds = () => {
    let fileIdsStr = configs.get('conf_FileIds');
    const fileIdsDef = configs.getObject('conf_FileIds');
    if (fileIdsDef !== null) {
        fileIdsStr = engine.findData(fileIdsDef);
    }
    if (fileIdsStr === null) {
        throw new Error('No File IDs.');
    }
    const fileIds =  fileIdsStr.split('\n').filter(key => key.length !== 0);
    if (fileIds.length === 0) {
        throw new Error('No File IDs.');
    }
    return fileIds;
};

const URL_TOKEN_REQUEST = 'https://oauth2.googleapis.com/token';
const SCOPE = 'https://www.googleapis.com/auth/drive.readonly';

/**
 * @param auth HTTP 認証設定
 * @returns {any} アクセストークンを含むオブジェクト
 */
const getAccessToken = (auth) => {
    const privateKeyId = auth.getPrivateKeyId();
    const privateKey = auth.getPrivateKey();
    const serviceAccount = auth.getCustomSecret1();
    const scope = auth.getScope();
    if (!scope.split(' ').includes(SCOPE)) {
        throw new Error(`Scope ${SCOPE} must be included in the scope.`);
    }
    if (privateKeyId === '') {
        throw new Error('Private Key ID is required.');
    }
    if (privateKey === '') {
        throw new Error('Private Key is required.');
    }
    if (serviceAccount === '') {
        throw new Error('Service Account must be set to Custom Secret 1.');
    }
    const header = {
        "alg": "RS256",
        "typ": "at+jwt",
        "kid": privateKeyId
    };
    const now = Math.floor(Date.now() / 1000);
    const payload = {
        "iss": serviceAccount,
        "aud": URL_TOKEN_REQUEST,
        "sub": '',
        "iat": now,
        "exp": now + 3600,
        /**
         * https://developers.google.com/identity/protocols/oauth2/service-account#jwt-auth
         * "without OAuth" の話だが、OAuth でも 1 hour になるようだ。
         * 1 hour より長ければエラー。短ければ、1 hour のトークンが返ってくる。
         */
        scope
    };
    const keyB = rsa.readKeyFromPkcs8(privateKey);
    const assertion = jwt.build(header, payload, keyB);

    const response = httpClient.begin()
        .formParam("grant_type", "urn:ietf:params:oauth:grant-type:jwt-bearer")
        .formParam('assertion', assertion)
        .post(URL_TOKEN_REQUEST);
    const responseText = response.getResponseAsString();
    if (response.getStatusCode() !== 200) {
        engine.log(responseText);
        throw new Error(`Failed to get Access token. status: ${response.getStatusCode()}`);
    }
    const result = JSON.parse(response.getResponseAsString());
    if (result.access_token === undefined) {
        engine.log(responseText);
        throw new Error(`Failed to get Access token. access token not found.`);
    }
    return result;
};

/**
 * ファイルメタデータ取得
 * @param auth HTTP 認証設定
 * @param fileId ファイルID
 */
const getFileMetadata = (auth, fileId) => {
    const URL = `https://www.googleapis.com/drive/v3/files/${encodeURIComponent(fileId)}`;

    const response = httpClient.begin()
        .oauth2JwtBearer(auth, () => getAccessToken(auth))
        .queryParam("supportsAllDrives", "true")
        .get(URL);

    const status = response.getStatusCode();
    const respTxt = response.getResponseAsString();
    if (status !== 200) {
        engine.log(respTxt);
        throw new Error(`Failed to get metadata of file. status: ${status}`);
    }
    const respJson = JSON.parse(respTxt);
    return {
        name: respJson.name,
        contentType: respJson.mimeType
    };
};

/**
 * ファイル取得
 * @param auth HTTP 認証設定
 * @param fileId ファイルID
 */
const getFile = (auth, fileId) => {
    const URL = `https://www.googleapis.com/drive/v3/files/${encodeURIComponent(fileId)}`;

    const response = httpClient.begin()
        .oauth2JwtBearer(auth, () => getAccessToken(auth))
        .queryParam("supportsAllDrives", "true")
        .queryParam("alt", "media")
        .get(URL);

    const status = response.getStatusCode();
    const respTxt = response.getResponseAsString();
    if (status !== 200) {
        engine.log(respTxt);
        throw new Error(`Failed to download file. status: ${status}`);
    }
    return response.getResponse();
};