bookstore

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A small data framework for collaborative list editing using Azure Blob Storage and Redis.

What is different than traditional CRUD + cache?

• Content and summary
  • Summary is computed from content, via a summarizer function
  • When content is updated, only summary is broadcasted via Redis to other nodes
  • List will fetch all summaries, without content
  • List is cheap, O(1)
• Update is done thru lock-update-unlock pattern with updater function
  • Updater function can be programmed as optimistic or pessimistic concurrency
  • We believe this model makes concurrency issues a little bit easier to handle

bookstore is designed to be exposed over Web Socket and Server-Sent Events.

How to use

For production build, npm install bookstore. For development build, npm install bookstore@master.

For peer dependencies, you will also need npm install azure-storage@2 redis.

const { createBlobService } = require('azure-storage');
const { createClient } = require('redis');
const updateIn = require('simple-update-in');
const createBook, { createPubSubUsingRedis, createStorageUsingAzureStorage } = require('bookstore');

const blobService = createBlobService(
  process.env.AZURE_STORAGE_ACCOUNT,
  process.env.AZURE_STORAGE_ACCESS_KEY
);

const publishRedis = createClient();
const subscribeRedis = publishRedis.duplicate();

const book = createBook(
  ({ x, y }) => ({ sum: x + y }),
  {
    ...createPubSubUsingRedis(publishRedis, subscribeRedis, 'blob-container-name'),
    ...createStorageUsingAzureStorage(blobService, 'blob-container-name')
  }
);

await book.create('page-0', { x: 1, y: 2 });

// Listing summary of all pages
// { 'page-0': {
//   summary: { sum: 3 }
// } }
await book.list();

// Getting the content of the page
// { x: 1, y: 2 }
await book.get('page-0');

// Update a page
// We use `simple-update-in` and updater function for handling concurrency
await book.update('page-0', content => updateIn(content, ['x'], () => 3));

// "change" event emitted when update broadcast on Redis
// Only summaries are sent over Redis
book.subscribe(({ id, summary }) => {
  console.log(id); // 'page-0'
  console.log(summary); // { sum: 5 }
});

// Listing summary of all pages again, with new changes
// { 'page-0': {
//   summary: { sum: 5 }
// } }
await book.list();

// Delete a page
await book.del('page-0');

Peer requirements

Instead of using Blob via Azure Storage and Pub-sub via Redis, you can also use other services as long as they met the requirements:

• Storage
  • create(id, content, summary): Create a new blob with content and summary
  • del(id): Delete a blob
  • get(id): Read a blob content
  • list(): List all blob summaries, without reading the actual content
  • update(id, updater): Update an existing blob via an updater function, using lock to prevent dirty read
    • updater: ({ content, summary }) => ({ content, summary })
• Pub-sub
  • publish(content): Publish to a predefined topic
  • subscribe(callback: content => void): () => void: Subscribe to a predefined topic via callback, will return a function for unsubscribe
    • callback will be called if content is updated (via Object.is) and summary has kept the same

Contributions

Like us? Star us.

Want to make it better? File us an issue.

Don't like something you see? Submit a pull request.

Changelog

[2.2.0] - 2019-02-18

Added

• Fix #1. summarizer will receive id of the page as the second argument, in PR #2.