git.squeep.com Git - websub-hub/blob - src/communication.js

   1 'use strict';
   2
   3 /**
   4  * Here we wrangle all outgoing requests, as well as the
   5  * worker which initiates most of them.
   6  */
   7
   8 const axios = require('axios');
   9 const common = require('./common');
  10 const crypto = require('crypto');
  11 const Enum = require('./enum');
  12 const Errors = require('./errors');
  13 const Worker = require('./worker');
  14 const LinkHelper = require('./link-helper');
  15 const { version: packageVersion, name: packageName } = require('../package.json'); // For default UA string
  16
  17 const { performance } = require('perf_hooks');
  18
  19 const _fileScope = common.fileScope(__filename);
  20
  21 class Communication {
  22   constructor(logger, db, options) {
  23     this.logger = logger;
  24     this.db = db;
  25     this.options = options;
  26     this.linkHelper = new LinkHelper(logger, options);
  27
  28     if (this.options.dingus.selfBaseUrl) {
  29       this.linkHub = `, <${this.options.dingus.selfBaseUrl}>; rel="hub"`;
  30     } else {
  31       this.linkHub = '';
  32       this.logger.error(_fileScope('constructor'), 'empty dingus.selfBaseUrl value, server responses will not be compliant');
  33     }
  34
  35     // Set common options
  36     this.axios = axios.create({
  37       validateStatus: null, // Non-success responses are not exceptional
  38       headers: {
  39         [Enum.Header.UserAgent]: Communication.userAgentString(options.userAgent),
  40       },
  41     });
  42
  43     this.axios.interceptors.request.use((request) => {
  44       request.startTimestampMs = performance.now();
  45       return request;
  46     });
  47     this.axios.interceptors.response.use((response) => {
  48       response.elapsedTimeMs = performance.now() - response.config.startTimestampMs;
  49       return response;
  50     });
  51
  52     this.worker = new Worker(logger, this.workFeed.bind(this), options);
  53     this.worker.start();
  54   }
  55
  56
  57   static userAgentString(userAgentConfig) {
  58     // eslint-disable-next-line security/detect-object-injection
  59     const _conf = (field, def) => (userAgentConfig && field in userAgentConfig) ? userAgentConfig[field] : def;
  60     const product = _conf('product', packageName);
  61     const version = _conf('version', packageVersion);
  62     let implementation = _conf('implementation', Enum.Specification);
  63     if (implementation) {
  64       implementation = ` (${implementation})`;
  65     }
  66     return `${product}/${version}${implementation}`;
  67   }
  68
  69
  70   /**
  71    * Generate a random string.
  72    * @param {Integer} bytes
  73    * @returns {String}
  74    */
  75   static async generateChallenge(bytes = 30) {
  76     return (await common.randomBytesAsync(bytes)).toString('base64');
  77   }
  78
  79
  80   /**
  81    * Generate the signature string for content.
  82    * @param {Buffer} message
  83    * @param {Buffer} secret
  84    * @param {String} algorithm
  85    * @returns {String}
  86    */
  87   static signature(message, secret, algorithm) {
  88     const hmac = crypto.createHmac(algorithm, secret);
  89     hmac.update(message);
  90     return `${algorithm}=${hmac.digest('hex')}`;
  91   }
  92
  93
  94   /**
  95    * Generate the hash for content.
  96    * @param {Buffer} content
  97    * @param {String} algorithm
  98    * @returns
  99    */
 100   static contentHash(content, algorithm) {
 101     const hash = crypto.createHash(algorithm);
 102     hash.update(content);
 103     return hash.digest('hex');
 104   }
 105
 106
 107   /**
 108    * A request skeleton config.
 109    * @param {String} method
 110    * @param {String} requestUrl
 111    * @param {String} body
 112    * @param {Object} params
 113    */
 114   static _axiosConfig(method, requestUrl, body, params = {}, headers = {}) {
 115     const urlObj = new URL(requestUrl);
 116     const config = {
 117       method,
 118       url: `${urlObj.origin}${urlObj.pathname}`,
 119       params: urlObj.searchParams,
 120       headers,
 121       ...(body && { data: body }),
 122       // Setting this does not appear to be enough to keep axios from parsing JSON response into object
 123       responseType: 'text',
 124       // So force the matter by eliding all response transformations
 125       transformResponse: [ (res) => res ],
 126     };
 127     Object.entries(params).map(([k, v]) => config.params.set(k, v));
 128     return config;
 129   }
 130
 131
 132   /**
 133    * Create request config for verifying an intent.
 134    * @param {URL} requestUrl
 135    * @param {String} topicUrl
 136    * @param {String} mode
 137    * @param {Integer} leaseSeconds
 138    * @param {String} challenge
 139    */
 140   static _intentVerifyAxiosConfig(requestUrl, topicUrl, mode, leaseSeconds, challenge) {
 141     // Explicitly convert leaseSeconds to string, due to some DB backends. (Looking at you, sqlite..)
 142     leaseSeconds = leaseSeconds.toString();
 143
 144     return Communication._axiosConfig('GET', requestUrl, undefined, {
 145       'hub.mode': mode,
 146       'hub.topic': topicUrl,
 147       'hub.challenge': challenge,
 148       'hub.lease_seconds': leaseSeconds,
 149     }, {});
 150   }
 151
 152
 153   /**
 154    * Create request config for denying an intent.
 155    * @param {String} requestUrl
 156    * @param {String} topicUrl
 157    * @param {String} reason
 158    * @returns {String}
 159    */
 160   static _intentDenyAxiosConfig(requestUrl, topicUrl, reason) {
 161     return Communication._axiosConfig('GET', requestUrl, undefined, {
 162       'hub.mode': Enum.Mode.Denied,
 163       'hub.topic': topicUrl,
 164       ...(reason && { 'hub.reason': reason }),
 165     }, {});
 166   }
 167
 168
 169   /**
 170    * Create request config for querying publisher for subscription validation.
 171    * @param {Topic} topic
 172    * @param {Verification} verification
 173    * @returns {String}
 174    */
 175   static _publisherValidationAxiosConfig(topic, verification) {
 176     const body = {
 177       callback: verification.callback,
 178       topic: topic.url,
 179       ...(verification.httpFrom && { from: verification.httpFrom }),
 180       ...(verification.httpRemoteAddr && { address: verification.httpRemoteAddr }),
 181     };
 182     return Communication._axiosConfig('POST', topic.publisherValidationUrl, body, {}, {
 183       [Enum.Header.ContentType]: Enum.ContentType.ApplicationJson,
 184     });
 185   }
 186
 187
 188   /**
 189    * Create request config for fetching topic content.
 190    * Prefer existing content-type, but accept anything.
 191    * @param {Topic} topic
 192    * @returns {String}
 193    */
 194   static _topicFetchAxiosConfig(topic) {
 195     const acceptWildcard = '*/*' + (topic.contentType ? ';q=0.9' : '');
 196     const acceptPreferred = [topic.contentType, acceptWildcard].filter((x) => x).join(', ');
 197     return Communication._axiosConfig('GET', topic.url, undefined, {}, {
 198       [Enum.Header.Accept]: acceptPreferred,
 199     });
 200   }
 201
 202
 203   /**
 204    * Attempt to verify a requested intent with client callback endpoint.
 205    * @param {*} dbCtx
 206    * @param {*} verificationId
 207    * @param {String} requestId
 208    * @returns {Boolean} whether to subsequently attempt next task if verification succeeds
 209    */
 210   async verificationProcess(dbCtx, verificationId, requestId) {
 211     const _scope = _fileScope('verificationProcess');
 212
 213     const verification = await this.db.verificationGetById(dbCtx, verificationId);
 214     if (!verification) {
 215       this.logger.error(_scope, 'no such verification', { verificationId, requestId });
 216       throw new Errors.InternalInconsistencyError('no such verification id');
 217     }
 218
 219     const topic = await this.db.topicGetById(dbCtx, verification.topicId);
 220     if (!topic) {
 221       this.logger.error(_scope, 'no such topic id', { verification, requestId });
 222       throw new Errors.InternalInconsistencyError('no such topic id');
 223     }
 224
 225     if (!topic.isActive) {
 226       this.logger.debug(_scope, 'topic not active, skipping verification', { verification, requestId });
 227       await this.db.verificationRelease(dbCtx, verificationId);
 228       return;
 229     }
 230
 231     // If topic is deleted, deny any subscriptions.
 232     // Un-subscriptions can continue to be verified.
 233     if (topic.isDeleted && verification.mode === Enum.Mode.Subscribe) {
 234       this.logger.info(_scope, 'topic is deleted, verification becomes denial', { verification, requestId });
 235
 236       verification.mode = Enum.Mode.Denied;
 237       verification.reason = 'Gone: topic no longer valid on this hub.';
 238       verification.isPublisherValidated = true;
 239       await this.db.verificationUpdate(dbCtx, verification);
 240     }
 241
 242     // If verification needs publisher validation, this delivery is for publisher.
 243     if (verification.mode === Enum.Mode.Subscribe && verification.isPublisherValidated === false) {
 244       this.logger.debug(_scope, 'attempting publisher validation', { verification, requestId });
 245       const continueVerification = await this.publisherValidate(dbCtx, topic, verification);
 246
 247       // If publisher validation completed, verification will proceed.
 248       // If not, we're done for now and shall try again later.
 249       if (!continueVerification) {
 250         this.logger.debug(_scope, 'publisher validation did not complete, belaying verification', { verification });
 251         await this.db.verificationIncomplete(dbCtx, verificationId, this.options.communication.retryBackoffSeconds);
 252         return;
 253       }
 254     }
 255
 256     const u = new URL(verification.callback);
 257     let callbackRequestConfig, challenge;
 258     if (verification.mode === Enum.Mode.Denied) {
 259       // Denials don't have a challenge.
 260       callbackRequestConfig = Communication._intentDenyAxiosConfig(u, topic.url, verification.reason);
 261     } else {
 262       // Subscriptions and unsubscriptions require challenge matching.
 263       challenge = await Communication.generateChallenge();
 264       callbackRequestConfig = Communication._intentVerifyAxiosConfig(u, topic.url, verification.mode, verification.leaseSeconds, challenge);
 265     }
 266
 267     const logInfoData = {
 268       callbackUrl: u.href,
 269       topicUrl: topic.url,
 270       mode: verification.mode,
 271       originalRequestId: verification.requestId,
 272       requestId,
 273       verificationId,
 274     };
 275
 276     this.logger.info(_scope, 'verification request', logInfoData);
 277
 278     let response;
 279     try {
 280       response = await this.axios(callbackRequestConfig);
 281     } catch (e) {
 282       this.logger.error(_scope, 'verification request failed', { ...logInfoData, error: e });
 283       await this.db.verificationIncomplete(dbCtx, verificationId, this.options.communication.retryBackoffSeconds);
 284       return;
 285     }
 286     logInfoData.response = common.axiosResponseLogData(response);
 287     this.logger.debug(_scope, 'verification response', logInfoData );
 288
 289     let verificationAccepted = true; // Presume success.
 290
 291     switch (common.httpStatusCodeClass(response.status)) {
 292       case 2:
 293         // Success, fall out of switch.
 294         break;
 295
 296       case 5:
 297         // Retry
 298         this.logger.info(_scope, 'verification remote server error', logInfoData );
 299         await this.db.verificationIncomplete(dbCtx, verificationId, this.options.communication.retryBackoffSeconds);
 300         return;
 301
 302       default:
 303         // Anything else is unsuccessful.
 304         this.logger.info(_scope, 'verification rejected by status', logInfoData );
 305         verificationAccepted = false;
 306     }
 307
 308     // Any denial is not accepted.
 309     if (verification.mode === Enum.Mode.Denied) {
 310       this.logger.info(_scope, 'verification denial accepted', logInfoData );
 311       verificationAccepted = false;
 312     }
 313
 314     if ([Enum.Mode.Subscribe, Enum.Mode.Unsubscribe].includes(verification.mode)
 315     &&  response.data !== challenge) {
 316       this.logger.info(_scope, 'verification rejected by challenge', logInfoData);
 317       verificationAccepted = false;
 318     }
 319
 320     await this.db.transaction(dbCtx, async (txCtx) => {
 321       switch (verification.mode) {
 322         case Enum.Mode.Subscribe:
 323           if (verificationAccepted) {
 324             await this.db.subscriptionUpsert(txCtx, verification);
 325           }
 326           break;
 327
 328         case Enum.Mode.Unsubscribe:
 329           if (verificationAccepted) {
 330             await this.db.subscriptionDelete(txCtx, verification.callback, verification.topicId);
 331           }
 332           break;
 333
 334         case Enum.Mode.Denied:
 335           await this.db.subscriptionDelete(txCtx, verification.callback, verification.topicId);
 336           break;
 337
 338         default:
 339           this.logger.error(_scope, 'unanticipated mode', { logInfoData });
 340           throw new Errors.InternalInconsistencyError(verification.mode);
 341       }
 342
 343       await this.db.verificationComplete(dbCtx, verificationId, verification.callback, verification.topicId);
 344     }); // txCtx
 345
 346     this.logger.info(_scope, 'verification complete', { ...logInfoData, verificationAccepted });
 347   }
 348
 349
 350   /**
 351    * Attempt to verify a pending subscription request with publisher.
 352    * Updates (and persists) verification.
 353    * Returns boolean of status of publisher contact, and hence
 354    * whether to continue verification with client.
 355    * @param {*} dbCtx
 356    * @param {TopicData} topic
 357    * @param {VerificationData} verification
 358    * @returns {Boolean}
 359    */
 360   async publisherValidate(dbCtx, topic, verification) {
 361     const _scope = _fileScope('publisherValidate');
 362     const publisherValidationRequestConfig = Communication._publisherValidationAxiosConfig(topic, verification);
 363     const logInfoData = {
 364       topicUrl: topic.url,
 365       callbackUrl: verification.callback,
 366       requestId: verification.requestId,
 367     };
 368     let response;
 369
 370     this.logger.info(_scope, 'publisher validation request', logInfoData);
 371
 372     try {
 373       response = await this.axios(publisherValidationRequestConfig);
 374     } catch (e) {
 375       this.logger.error(_scope, 'publisher validation failed', { ...logInfoData, error: e });
 376       return false; // Do not continue with client verification.
 377     }
 378
 379     logInfoData.response = common.axiosResponseLogData(response);
 380     this.logger.debug(_scope, 'validation response', logInfoData);
 381
 382     let verificationNeedsUpdate = false;
 383     switch (common.httpStatusCodeClass(response.status)) {
 384       case 2:
 385         this.logger.info(_scope, 'publisher validation complete, allowed', logInfoData);
 386         break;
 387
 388       case 5:
 389         this.logger.info(_scope, 'publisher validation remote server error', logInfoData);
 390         return false; // Do not continue with client verification.
 391
 392       default:
 393         this.logger.info(_scope, 'publisher validation complete, denied', logInfoData);
 394         // Change client verification
 395         verification.mode = Enum.Mode.Denied;
 396         verification.reason = 'publisher rejected request'; // TODO: details from response?
 397         verificationNeedsUpdate = true;
 398     }
 399
 400     // Success from publisher, either accepted or denied.
 401     // Set validated flag, and allow client verification to continue.
 402     await this.db.transaction(dbCtx, async (txCtx) => {
 403       if (verificationNeedsUpdate) {
 404         await this.db.verificationUpdate(txCtx, verification.id, verification);
 405       }
 406       await this.db.verificationValidated(txCtx, verification.id);
 407     });
 408     return true;
 409   }
 410
 411
 412   /**
 413    * Retrieve content from a topic.
 414    * @param {*} dbCtx
 415    * @param {*} topicId
 416    * @param {String} requestId
 417    * @returns
 418    */
 419   async topicFetchProcess(dbCtx, topicId, requestId) {
 420     const _scope = _fileScope('topicFetchProcess');
 421     const logInfoData = {
 422       topicId,
 423       requestId,
 424     };
 425
 426     this.logger.debug(_scope, 'called', logInfoData);
 427
 428     const topic = await this.db.topicGetById(dbCtx, topicId);
 429     if (topic === undefined) {
 430       this.logger.error(_scope, 'no such topic id', logInfoData);
 431       throw new Errors.InternalInconsistencyError('no such topic id');
 432     }
 433
 434     logInfoData.url = topicId.url;
 435
 436     if (topic.isDeleted) {
 437       this.logger.debug(_scope, 'topic deleted, skipping update request', logInfoData);
 438       return;
 439     }
 440
 441     const updateRequestConfig = Communication._topicFetchAxiosConfig(topic);
 442
 443     this.logger.info(_scope, 'topic update request', logInfoData);
 444
 445     let response;
 446     try {
 447       response = await this.axios(updateRequestConfig);
 448     } catch (e) {
 449       this.logger.error(_scope, 'update request failed', logInfoData);
 450       await this.db.topicFetchIncomplete(dbCtx, topicId, this.options.communication.retryBackoffSeconds);
 451       return;
 452     }
 453     logInfoData.response = common.axiosResponseLogData(response);
 454     this.logger.debug(_scope, 'fetch response', logInfoData);
 455
 456     switch (common.httpStatusCodeClass(response.status)) {
 457       case 2:
 458         // Fall out of switch on success
 459         break;
 460
 461       case 5:
 462         this.logger.info(_scope, 'update remote server error', logInfoData);
 463         await this.db.topicFetchIncomplete(dbCtx, topicId, this.options.communication.retryBackoffSeconds);
 464         return;
 465
 466       default:
 467         this.logger.info(_scope, 'fetch failed by status', logInfoData);
 468         await this.db.topicFetchIncomplete(dbCtx, topicId, this.options.communication.retryBackoffSeconds);
 469         return;
 470     }
 471
 472     const contentHash = Communication.contentHash(response.data, topic.contentHashAlgorithm);
 473     logInfoData.contentHash = contentHash;
 474     if (topic.contentHash === contentHash) {
 475       this.logger.info(_scope, 'content has not changed', logInfoData);
 476       await this.db.topicFetchComplete(dbCtx, topicId);
 477       return;
 478     }
 479
 480     const validHub = await this.linkHelper.validHub(topic.url, response.headers, response.data);
 481     if (!validHub) {
 482       this.logger.debug(_scope, 'retrieved topic does not list us as hub', { logInfoData });
 483       if (this.options.communication.strictTopicHubLink) {
 484         await this.db.transaction(dbCtx, async (txCtx) => {
 485           // Set as deleted and set content_updated so subscriptions are notified.
 486           await this.db.topicDeleted(txCtx, topicId);
 487           await this.db.topicFetchComplete(txCtx, topicId);
 488         });
 489         return;
 490       }
 491     }
 492
 493     const contentType = response.headers[Enum.Header.ContentType.toLowerCase()];
 494
 495     await this.db.transaction(dbCtx, async (txCtx) => {
 496       await this.db.topicSetContent(txCtx, {
 497         topicId,
 498         content: Buffer.from(response.data),
 499         contentHash,
 500         ...(contentType && { contentType }),
 501       });
 502
 503       await this.db.topicFetchComplete(txCtx, topicId);
 504     });
 505     this.logger.info(_scope, 'content updated', logInfoData);
 506   }
 507
 508
 509   /**
 510    * Attempt to deliver a topic's content to a subscription.
 511    * @param {*} dbCtx
 512    * @param {String} callback
 513    * @param {*} topicId
 514    * @param {String} requestId
 515    */
 516   async subscriptionDeliveryProcess(dbCtx, subscriptionId, requestId) {
 517     const _scope = _fileScope('subscriptionDeliveryProcess');
 518
 519     const logInfoData = {
 520       subscriptionId,
 521       requestId,
 522     };
 523
 524     this.logger.debug(_scope, 'called', logInfoData);
 525
 526     const subscription = await this.db.subscriptionGetById(dbCtx, subscriptionId);
 527     if (!subscription) {
 528       this.logger.error(_scope, 'no such subscription', logInfoData);
 529       throw new Errors.InternalInconsistencyError('no such subscription');
 530     }
 531
 532     logInfoData.callback = subscription.callback;
 533
 534     const topic = await this.db.topicGetContentById(dbCtx, subscription.topicId);
 535     if (!topic) {
 536       this.logger.error(_scope, 'no such topic', logInfoData);
 537       throw new Errors.InternalInconsistencyError('no such topic');
 538     }
 539
 540     if (topic.isDeleted) {
 541       // If a topic has been set deleted, it does not list us as a valid hub.
 542       // Queue an unsubscription.
 543       const verification = {
 544         topicId: subscription.topicId,
 545         callback: subscription.callback,
 546         mode: Enum.Mode.Denied,
 547         reason: 'Gone: topic no longer valid on this hub.',
 548         isPublisherValidated: true,
 549         requestId,
 550       };
 551
 552       await this.db.transaction(dbCtx, async (txCtx) => {
 553         await this.db.verificationInsert(txCtx, verification);
 554         await this.db.subscriptionDeliveryComplete(txCtx, subscription.callback, subscription.topicId);
 555       });
 556       this.logger.info(_scope, 'update unsubscription for deleted topic', logInfoData);
 557       return;
 558     }
 559
 560     logInfoData.contentLength = topic.content.length;
 561     logInfoData.contentHash = topic.contentHash;
 562
 563     const updateAxiosConfig = Communication._axiosConfig('POST', subscription.callback, topic.content, {}, {
 564       [Enum.Header.Link]: `<${topic.url}>; rel="self"${this.linkHub}`,
 565       [Enum.Header.ContentType]: topic.contentType || Enum.ContentType.TextPlain,
 566       ...(subscription.secret && { [Enum.Header.XHubSignature]: Communication.signature(topic.content, subscription.secret, subscription.signatureAlgorithm) }),
 567     });
 568
 569     this.logger.info(_scope, 'update request', logInfoData);
 570
 571     let response;
 572     try {
 573       response = await this.axios(updateAxiosConfig);
 574     } catch (e) {
 575       this.logger.error(_scope, 'update request failed', { ...logInfoData, error: e });
 576       await this.db.subscriptionDeliveryIncomplete(dbCtx, subscription.callback, subscription.topicId, this.options.communication.retryBackoffSeconds);
 577       return;
 578     }
 579     logInfoData.response = common.axiosResponseLogData(response);
 580     this.logger.debug(_scope, 'update response', logInfoData);
 581
 582     switch (common.httpStatusCodeClass(response.status)) {
 583       case 2:
 584         // Fall out of switch on success.
 585         break;
 586
 587       case 5:
 588         this.logger.info(_scope, 'update remote server error', logInfoData);
 589         await this.db.subscriptionDeliveryIncomplete(dbCtx, subscription.callback, subscription.topicId, this.options.communication.retryBackoffSeconds);
 590         return;
 591
 592       case 4:
 593         if (response.status === 410) { // GONE
 594           this.logger.info(_scope, 'client declined further updates', logInfoData);
 595           await this.db.subscriptionDeliveryGone(dbCtx, subscription.callback, subscription.topicId);
 596           return;
 597         }
 598         // All other 4xx falls through as failure
 599
 600       default:
 601         this.logger.info(_scope, 'update failed with non-2xx status code', logInfoData);
 602         await this.db.subscriptionDeliveryIncomplete(dbCtx, subscription.callback, subscription.topicId, this.options.communication.retryBackoffSeconds);
 603         return;
 604     }
 605
 606     await this.db.subscriptionDeliveryComplete(dbCtx, subscription.callback, subscription.topicId);
 607     this.logger.info(_scope, 'update success', logInfoData);
 608   }
 609
 610
 611   /**
 612    * Claim and work a specific topic fetch task.
 613    * @param {*} dbCtx
 614    * @param {*} id
 615    * @param {String} requestId
 616    */
 617   async topicFetchClaimAndProcessById(dbCtx, topicId, requestId) {
 618     const _scope = _fileScope('topicFetchClaimAndProcessById');
 619
 620     const claimResult = await this.db.topicFetchClaimById(dbCtx, topicId, this.options.communication.claimTimeoutSeconds, this.options.nodeId);
 621     if (claimResult.changes != 1) {
 622       this.logger.debug(_scope, 'did not claim topic fetch', { topicId, requestId });
 623       return;
 624     }
 625     await this.topicFetchProcess(dbCtx, topicId, requestId);
 626   }
 627
 628
 629   /**
 630    * Claim and work a specific verification confirmation task.
 631    * @param {*} dbCtx
 632    * @param {*} verificationId
 633    * @param {String} requestId
 634    * @returns
 635    */
 636   async verificationClaimAndProcessById(dbCtx, verificationId, requestId) {
 637     const _scope = _fileScope('verificationClaimAndProcessById');
 638
 639     const claimResult = await this.db.verificationClaimById(dbCtx, verificationId, this.options.communication.claimTimeoutSeconds, this.options.nodeId);
 640     if (claimResult.changes != 1) {
 641       this.logger.debug(_scope, 'did not claim verification', { verificationId, requestId });
 642       return;
 643     }
 644     await this.verificationProcess(dbCtx, verificationId, requestId);
 645   }
 646
 647
 648   /**
 649    *
 650    * @param {Number} wanted maximum tasks to claim
 651    * @returns {Promise<void>[]}
 652    */
 653   async workFeed(wanted) {
 654     const _scope = _fileScope('workFeed');
 655     const inProgress = [];
 656     const requestId = common.requestId();
 657     const claimTimeoutSeconds = this.options.communication.claimTimeoutSeconds;
 658     const nodeId = this.options.nodeId;
 659     let topicFetchPromises = [], verificationPromises = [], updatePromises = [];
 660
 661     this.logger.debug(_scope, 'called', { wanted });
 662
 663     try {
 664       await this.db.context(async (dbCtx) => {
 665         if (wanted > 0) {
 666           // Update topics before anything else.
 667           const topicFetchIds = await this.db.topicFetchClaim(dbCtx, wanted, claimTimeoutSeconds, nodeId);
 668           // Each task gets a new context, as these map to connections in some dbs.
 669           // This dbCtx goes away after launching the processing functions, so would not be available to tasks.
 670           topicFetchPromises = topicFetchIds.map((id) => this.db.context((ctx) => this.topicFetchProcess(ctx, id, requestId)));
 671           inProgress.push(...topicFetchPromises);
 672           wanted -= topicFetchPromises.length;
 673         }
 674
 675         if (wanted > 0) {
 676           // Then any pending verifications.
 677           const verifications = await this.db.verificationClaim(dbCtx, wanted, claimTimeoutSeconds, nodeId);
 678           verificationPromises = verifications.map((id) => this.db.context((ctx) => this.verificationProcess(ctx, id, requestId)));
 679           inProgress.push(...verificationPromises);
 680           wanted -= verificationPromises.length;
 681         }
 682
 683         if (wanted > 0) {
 684           // Finally dole out content.
 685           const updates = await this.db.subscriptionDeliveryClaim(dbCtx, wanted, claimTimeoutSeconds, nodeId);
 686           updatePromises = updates.map((id) => this.db.context((ctx) => this.subscriptionDeliveryProcess(ctx, id, requestId)));
 687           inProgress.push(...updatePromises);
 688           wanted -= updatePromises.length;
 689         }
 690       }); // dbCtx
 691     } catch (e) {
 692       this.logger.error(_scope, 'failed', { error: e });
 693       // do not re-throw, return what we've claimed so far
 694     }
 695     this.logger.debug(_scope, 'searched for work', { topics: topicFetchPromises.length, verifications: verificationPromises.length, updates: updatePromises.length, wantedRemaining: wanted, requestId });
 696
 697     return inProgress;
 698   }
 699
 700
 701 }
 702
 703 module.exports = Communication;