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IBM Cloudant Node.js SDK Version 0.11.0

IBM Cloudant Node.js SDK is a client library that interacts with the IBM Cloudant APIs.

Disclaimer: This library is still a 0.x release. We do consider this library production-ready and capable, but there are still some limitations we’re working to resolve, and refinements we want to deliver. We are working really hard to minimise the disruption from now until the 1.0 release, but there may still be some changes that impact applications using this SDK. For now, be sure to pin versions to avoid surprises.

• Overview
• Features
• Prerequisites
• Installation
• Using the SDK
  • Authentication
    • Authentication with environment variables
      • IAM API key authentication
      • IAM Trusted profile (container) authentication
      • IAM Trusted profile (VPC) authentication
      • Session cookie authentication
    • Authentication with external configuration
    • Programmatic authentication
  • Automatic retries
  • Request timeout configuration
  • Code examples
    • 1. Create a database and add a document
    • 2. Retrieve information from an existing database
    • 3. Update your previously created document
    • 4. Delete your previously created document
    • Further code examples
  • Error handling
  • Raw IO
  • Further resources
  • Browser usage
    • Polyfills
    • CORS
  • Changes feed follower (beta)
    • Introduction
    • Modes of operation
    • Configuring the changes follower
    • Error suppression
    • Follower operation
    • Checkpointing
    • Code examples
      • Initializing a changes follower
      • Starting the changes follower
        • Start mode for continuous listening
        • Start mode for one-off fetching
      • Processing changes
        • Process continuous changes
        • Process one-off changes
      • Stopping the changes follower
• Questions
• Issues
• Versioning and LTS support
• Open source at IBM
• Contributing
• License

Overview

The IBM Cloudant Node.js SDK allows developers to programmatically interact with IBM Cloudant with the help of the @ibm-cloud/cloudant package.

Features

The purpose of this Node.js SDK is to wrap most of the HTTP request APIs provided by Cloudant and supply other functions to ease the usage of Cloudant. This SDK should make life easier for programmers to do what’s really important to them: developing software.

Reasons why you should consider using Cloudant Node.js SDK in your project:

• Supported by IBM Cloudant.
• Server compatibility with:
  • IBM Cloudant.
  • Apache CouchDB 3.x for data operations.
• Includes all the most popular and latest supported endpoints for applications.
• Handles the authentication.
• Familiar user experience with IBM Cloud SDKs.
• Flexibility to use either built-in models or byte-based requests and responses for documents.
• Built-in Changes feed follower (beta)
• Promise based design with asynchronous HTTP requests.
• Use either as native JavaScript or take advantage of TypeScript models.
• Transparently compresses request and response bodies.

Prerequisites

• A Cloudant service instance or a CouchDB server.
• Node.js 18, 20, or 22.

Installation

npm install @ibm-cloud/cloudant

Using the SDK

For fundamental SDK usage information and config options, please see the common IBM Cloud SDK documentation.

This library requires configuration with a service URL and Cloudant service credentials to authenticate with your account.

There are several ways to set these authentication properties:

1. As environment variables
2. The programmatic approach
3. With an external credentials file

The following section describes the different authentication types and provides environment variable examples. Examples for other configuration methods are available by following the provided links.

Authentication

This library requires credentials to authenticate with IBM Cloudant. These credentials may be:

• IBM Cloud IAM credentials (can be used with authentication types CONTAINER, VPC and IAM)
  • IBM Cloud account user, service ID or trusted profile credentials that have been granted access to the IBM Cloud Cloudant resource instance.
  • IBM Cloudant service credentials generated by the IBM Cloud Cloudant resource instance.
• Username and password credentials (can be used with authentication types COUCHDB_SESSION and BASIC)
  • IBM Cloudant service credentials generated for an IBM Cloud Cloudant resource instance not configured as IAM only.
  • IBM Cloudant legacy credentials (i.e. username and password) for instances not in IBM Cloud.
  • IBM Cloudant legacy API keys.

For other compatible APIs that are not Cloudant accounts (e.g. Apache CouchDB) non-IAM based authentication types must be used.

This table summarizes the available authentication types. The authentication types are listed in order of recommendation, preferably use the authentication type from the first row in the table that is compatible with your environment.

The default authentication type for the SDK is CONTAINER unless APIKEY configuration is supplied, which changes the default authentication type to IAM.

Authentication with environment variables

The default service name is CLOUDANT so CLOUDANT_ prefixed names are used in these examples.

Any custom service name prefix can be used as long as the matching name is used to instantiate the SDK client and the same prefix is used for all configuration options.

IAM API key authentication

For Cloudant IAM API key authentication, set the following environmental variables by replacing the <url> and <apikey> with your proper service credentials. There is no need to set CLOUDANT_AUTH_TYPE to IAM because it is the default when an APIKEY is set.

CLOUDANT_URL=<url>
CLOUDANT_APIKEY=<apikey>

IAM Trusted profile (container) authentication

For Cloudant IAM Trusted profile compute resource container authentication, set the following environmental variables by replacing the <url> and <id> with your values. There is no need to set CLOUDANT_AUTH_TYPE to CONTAINER because it is the default.

CLOUDANT_URL=<url>
CLOUDANT_IAM_PROFILE_ID=<id>

Alternatively a profile name may be used instead of an ID by replacing CLOUDANT_IAM_PROFILE_ID with CLOUDANT_IAM_PROFILE_NAME.

IAM Trusted profile (VPC) authentication

For Cloudant IAM Trusted profile compute resource vpc authentication, set the following environmental variables by replacing the <url> and <id> with your values.

CLOUDANT_AUTH_TYPE=VPC
CLOUDANT_URL=<url>
CLOUDANT_IAM_PROFILE_ID=<id>

Alternatively a profile CRN may be used instead of an ID by replacing CLOUDANT_IAM_PROFILE_ID with CLOUDANT_IAM_PROFILE_CRN.

Session cookie authentication

For COUCHDB_SESSION authentication, set the following environmental variables by replacing the <url>, <username> and <password> with your proper service credentials.

CLOUDANT_AUTH_TYPE=COUCHDB_SESSION
CLOUDANT_URL=<url>
CLOUDANT_USERNAME=<username>
CLOUDANT_PASSWORD=<password>

Authentication with external configuration

To use an external configuration file, the Cloudant API docs, or the general SDK usage information will guide you.

Programmatic authentication

To learn more about how to use programmatic authentication, see the related documentation in the Cloudant API docs or in the Node.js SDK Core document about authentication.

Automatic retries

The SDK supports a generalized retry feature that can automatically retry on common errors.

The automatic retries section has details on how to enable the retries with default values and customize the retries programmatically or with external configuration.

Request timeout configuration

No request timeout is defined, but a 2.5m connect and 2.5m read timeout is set by default. Be sure to set a request timeout appropriate to your application usage and environment. The request timeout section contains details on how to change the value.

Note: System settings may take precedence over configured timeout values.

Code examples

The following code examples authenticate with the environment variables.

1. Create a database and add a document

Note: This example code assumes that orders database does not exist in your account.

This example code creates orders database and adds a new document "example" into it. To connect, you must set your environment variables with the service url, authentication type and authentication credentials of your Cloudant service.

Cloudant environment variable naming starts with a service name prefix that identifies your service. By default, this is CLOUDANT, see the settings in the authentication with environment variables section.

If you would like to rename your Cloudant service from CLOUDANT, you must use your defined service name as the prefix for all Cloudant related environment variables.

Once the environment variables are set, you can try out the code examples.

import { CloudantV1 } from '@ibm-cloud/cloudant';

interface OrderDocument extends CloudantV1.Document {
  name?: string;
  joined?: string;
  _id: string;
  _rev?: string;
}

// 1. Create a client with `CLOUDANT` default service name ======================
const client = CloudantV1.newInstance({});

// 2. Create a database =========================================================
const exampleDbName = 'orders';

// Try to create database if it doesn't exist
const createDb = client
  .putDatabase({ db: exampleDbName })
  .then((putDatabaseResult) => {
    if (putDatabaseResult.result.ok) {
      console.log(`"${exampleDbName}" database created."`);
    }
  })
  .catch((err) => {
    if (err.code === 412) {
      console.log(
        `Cannot create "${exampleDbName}" database, it already exists.`
      );
    }
  });

// 3. Create a document =========================================================
// Create a document object with "example" id
const exampleDocId = 'example';

// Setting `_id` for the document is optional when postDocument function is used for CREATE.
// When `_id` is not provided the server will generate one for your document.
const exampleDocument: OrderDocument = { _id: exampleDocId };

// Add "name" and "joined" fields to the document
exampleDocument.name = 'Bob Smith';
exampleDocument.joined = '2019-01-24T10:42:59.000Z';

// Save the document in the database with "postDocument" function
createDb.then(() => {
  client
    .postDocument({
      db: exampleDbName,
      document: exampleDocument,
    })
    // ==========================================================================
    // Note: saving the document can also be done with the "putDocument"
    // function. In this case `docId` is required for a CREATE operation:
    /*
    .putDocument({
      db: exampleDbName,
      docId: exampleDocId,
      document: exampleDocument,
    })
    */
    // ==========================================================================
    .then((createDocumentResponse) => {
      // Keeping track of the revision number of the document object
      // is necessary for further UPDATE/DELETE operations:
      exampleDocument._rev = createDocumentResponse.result.rev;
      console.log(
        'You have created the document:\n' +
          JSON.stringify(exampleDocument, null, 2)
      );
    });
});

import { CloudantV1 } from '@ibm-cloud/cloudant';

const createDbAndDoc = async () => {
  // 1. Create a client with `CLOUDANT` default service name ====================
  const client = CloudantV1.newInstance({});

  // 2. Create a database =======================================================
  const exampleDbName = 'orders';

  // Try to create database if it doesn't exist
  try {
    const putDatabaseResult = (
      await client.putDatabase({
        db: exampleDbName,
      })
    ).result;
    if (putDatabaseResult.ok) {
      console.log(`"${exampleDbName}" database created.`);
    }
  } catch (err) {
    if (err.code === 412) {
      console.log(
        `Cannot create "${exampleDbName}" database, it already exists.`
      );
    }
  }

  // 3. Create a document =======================================================
  // Create a document object with "example" id
  const exampleDocId = 'example';

  // Setting `_id` for the document is optional when "postDocument" function is used for CREATE.
  // When `_id` is not provided the server will generate one for your document.
  const exampleDocument = { _id: exampleDocId };

  // Add "name" and "joined" fields to the document
  exampleDocument['name'] = 'Bob Smith';
  exampleDocument.joined = '2019-01-24T10:42:59.000Z';

  // Save the document in the database with "postDocument" function
  const createDocumentResponse = await client.postDocument({
    db: exampleDbName,
    document: exampleDocument,
  });

  // ==========================================================================
  // Note: saving the document can also be done with the "putDocument"
  // function. In this case `docId` is required for a CREATE operation:
  /* const createDocumentResponse = await client.putDocument({
       db: exampleDbName,
       docId: exampleDocId,
       document: exampleDocument,
  }); */
  // ==========================================================================

  // Keeping track of the revision number of the document object
  // is necessary for further UPDATE/DELETE operations:
  exampleDocument._rev = createDocumentResponse.result.rev;
  console.log(
    'You have created the document:\n' +
      JSON.stringify(exampleDocument, null, 2)
  );
};

if (require.main === module) {
  createDbAndDoc();
}

When you run the code, you see a result similar to the following output.

"orders" database created.
You have created the document:
{
  "_id": "example",
  "name": "Bob Smith",
  "joined": "2019-01-24T10:42:59.000Z",
  "_rev": "1-1b403633540686aa32d013fda9041a5d"
}

2. Retrieve information from an existing database

Note: This example code assumes that you have created both the orders database and the example document by running the previous example code successfully. Otherwise, the following error message occurs, "Cannot delete document because either 'orders' database or 'example' document was not found."

import { CloudantV1 } from '@ibm-cloud/cloudant';

// 1. Create a client with `CLOUDANT` default service name =====================
const client = CloudantV1.newInstance({});

// 2. Get server information ====================================================
// call service without parameters:
client.getServerInformation().then((serverInformation) => {
  const { version } = serverInformation.result;
  console.log(`Server version ${version}`);
});

// 3. Get database information for "orders" ===================================
const dbName = 'orders';

// call service with embedded parameters:
client.getDatabaseInformation({ db: dbName }).then((dbInfo) => {
  const documentCount = dbInfo.result.docCount;
  const dbNameResult = dbInfo.result.dbName;

  // 4. Show document count in database =========================================
  console.log(
    `Document count in "${dbNameResult}" database is ${documentCount}.`
  );
});

// 5. Get "example" document out of the database by document id =====================
const getDocParams: CloudantV1.GetDocumentParams = {
  db: dbName,
  docId: 'example',
};

// call service with predefined parameters:
client.getDocument(getDocParams).then((documentExample) => {
  // result object is defined as a Document here:
  const { result } = documentExample;
  console.log(
    `Document retrieved from database:\n${JSON.stringify(result, null, 2)}`
  );
});

import { CloudantV1 } from '@ibm-cloud/cloudant';

const getInfoFromExistingDatabase = async () => {
  // 1. Create a client with `CLOUDANT` default service name  ===================
  const client = CloudantV1.newInstance({});

  // 2. Get server information ==================================================
  // call service without parameters:
  const { version } = (await client.getServerInformation()).result;
  console.log(`Server version ${version}`);

  // 3. Get database information for "orders" =================================
  const dbName = 'orders';

  // call service with embedded parameters:
  const dbInfo = await client.getDatabaseInformation({ db: dbName });
  const documentCount = dbInfo.result.docCount;
  const dbNameResult = dbInfo.result.dbName;

  // 4. Show document count in database =========================================
  console.log(
    `Document count in "${dbNameResult}" database is ${documentCount}.`
  );

  // 5. Get "example" document out of the database by document id ===================
  const getDocParams = { db: dbName, docId: 'example' };

  // call service with predefined parameters:
  const documentExample = await client.getDocument(getDocParams);

  // result object is defined as a Document here:
  const { result } = documentExample;

  console.log(
    `Document retrieved from database:\n${JSON.stringify(result, null, 2)}`
  );
};

if (require.main === module) {
  getInfoFromExistingDatabase();
}

Server version 3.2.1
Document count in "orders" database is 1.
Document retrieved from database:
{
  "_id": "example",
  "_rev": "1-1b403633540686aa32d013fda9041a5d",
  "name": "Bob Smith",
  "joined": "2019-01-24T10:42:59.000Z"
}

3. Update your previously created document

Note: This example code assumes that you have created both the orders database and the example document by running the previous example code successfully. Otherwise, the following error message occurs, "Cannot update document because either 'orders' database or 'example' document was not found."

import { CloudantV1 } from '@ibm-cloud/cloudant';

interface OrderDocument extends CloudantV1.Document {
  address?: string;
  joined?: string;
  _id?: string;
  _rev?: string;
}

// 1. Create a client with `CLOUDANT` default service name ======================
const client = CloudantV1.newInstance({});
// 2. Update the document =======================================================
// Set the options to get the document out of the database if it exists
const exampleDbName = 'orders';

// Try to get the document if it previously existed in the database
const getDocParams: CloudantV1.GetDocumentParams = {
  docId: 'example',
  db: exampleDbName,
};

// ==============================================================================
// Note : for response byte stream use:
/*
const getdocAsStreamParam: CloudantV1.GetDocumentAsStreamParams = {
  docId: 'example',
  db: exampleDbName,
};
client
  .getDocumentAsStream(getdocAsStreamParam)
  .then((documentAsByteStream) => {...});
*/
// ==============================================================================

client
  .getDocument(getDocParams)
  .then((docResult) => {
    // using OrderDocument on getDocument result:
    const document: OrderDocument = docResult.result;

    // Add Bob Smith's address to the document
    document.address = '19 Front Street, Darlington, DL5 1TY';

    // Remove the joined property from document object
    delete document.joined;

    // Update the document in the database
    client
      .postDocument({ db: exampleDbName, document })
      // ========================================================================
      // Note 1: for request byte stream use:
      // .postDocument(
      //   {db: exampleDbName, document: documentAsByteStream}
      // )
      // ========================================================================

      // ========================================================================
      // Note 2: updating the document can also be done with the "putDocument" function.
      // `docId` and `rev` are required for an UPDATE operation,
      // but `rev` can be provided in the document object as `_rev` too:
      /*
      .putDocument({
        db: exampleDbName,
        docId: document._id, // docId is a required parameter
        rev: document._rev,
        document, // _rev in the document object CAN replace above `rev` parameter
      })
      */
      // ========================================================================
      .then((res) => {
        // Keeping track of the latest revision number of the document object
        // is necessary for further UPDATE/DELETE operations:
        document._rev = res.result.rev;
        console.log(
          `You have updated the document:\n${JSON.stringify(document, null, 2)}`
        );
      });
  })
  .catch((err) => {
    if (err.code === 404) {
      console.log(
        `Cannot update document because either "${exampleDbName}" database or the "example" ` +
          `document was not found.`
      );
    }
  });

import { CloudantV1 } from '@ibm-cloud/cloudant';

const updateDoc = async () => {
  // 1. Create a client with `CLOUDANT` default service name ====================
  const client = CloudantV1.newInstance({});
  // 2. Update the document =====================================================
  // Set the options to get the document out of the database if it exists
  const exampleDbName = 'orders';

  // Try to get the document if it previously existed in the database
  try {
    const document = (
      await client.getDocument({
        docId: 'example',
        db: exampleDbName,
      })
    ).result;

    // ==========================================================================
    // Note: for response byte stream use:
    /*
    const documentAsByteStream = (
      await client.getDocumentAsStream({
        docId: 'example',
        db: exampleDbName,
      })
    ).result;
    */
    // ==========================================================================

    // Add Bob Smith's address to the document
    document.address = '19 Front Street, Darlington, DL5 1TY';

    // Remove the joined property from document object
    delete document['joined'];

    // Keeping track of the latest revision number of the document object
    // is necessary for further UPDATE/DELETE operations:
    document._rev = (
      await client.postDocument({
        db: exampleDbName,
        document, // _id and _rev MUST be inside the document object
      })
    ).result.rev;

    // ==========================================================================
    // Note 1: for request byte stream use:
    /*
    document._rev = (
      await client.postDocument({
        db: exampleDbName,
        document: documentAsByteStream,
      })
    ).result.rev;
     */
    // ==========================================================================

    // ==========================================================================
    // Note 2: updating the document can also be done with the "putDocument" function.
    // `docId` and `rev` are required for an UPDATE operation,
    // but `rev` can be provided in the document object as `_rev` too:
    /*
    document._rev = (
      await client.putDocument({
        db: exampleDbName,
        docId: document._id, // docId is a required parameter
        rev: document._rev,
        document // _rev in the document object CAN replace above `rev` parameter
      })
    ).result.rev;
    */
    // ==========================================================================

    console.log(
      `You have updated the document:\n${JSON.stringify(document, null, 2)}`
    );
  } catch (err) {
    if (err.code === 404) {
      console.log(
        `Cannot update document because either "${exampleDbName}" database or the "example" ` +
          `document was not found.`
      );
    }
  }
};

if (require.main === module) {
  updateDoc();
}

You have updated the document:
{
  "_id": "example",
  "_rev": "2-4e2178e85cffb32d38ba4e451f6ca376",
  "name": "Bob Smith",
  "address": "19 Front Street, Darlington, DL5 1TY"
}

4. Delete your previously created document

Note: This example code assumes that you have created both the orders database and the example document by running the previous example code successfully. Otherwise, the following error message occurs, "Cannot delete document because either 'orders' database or 'example' document was not found."

import { CloudantV1 } from '@ibm-cloud/cloudant';

interface OrderDocument extends CloudantV1.Document {
  name?: string;
  address?: string;
  joined?: string;
  _id?: string;
  _rev?: string;
}

// 1. Create a client with `CLOUDANT` default service name ======================
const client = CloudantV1.newInstance({});

// 2. Delete the document =======================================================
// Set the options to get the document out of the database if it exists
const exampleDbName = 'orders';
const exampleDocId = 'example';

// Try to get the document if it previously existed in the database
const getDocParams: CloudantV1.GetDocumentParams = {
  docId: exampleDocId,
  db: exampleDbName,
};

client
  .getDocument(getDocParams)
  .then((docResult) => {
    const document: OrderDocument = docResult.result;

    client
      .deleteDocument({
        db: exampleDbName,
        docId: document._id, // `docId` is required for DELETE
        rev: document._rev, // `rev` is required for DELETE
      })
      .then(() => {
        console.log('You have deleted the document.');
      });
  })
  .catch((err) => {
    if (err.code === 404) {
      console.log(
        `Cannot delete document because either "${exampleDbName}" database or the "example" ` +
          `document was not found.`
      );
    }
  });

import { CloudantV1 } from '@ibm-cloud/cloudant';

const deleteDoc = async () => {
  // 1. Create a client with `CLOUDANT` default service name ====================
  const client = CloudantV1.newInstance({});

  // 2. Delete the document =====================================================
  // Set the options to get the document out of the database if it exists
  const exampleDbName = 'orders';
  const exampleDocId = 'example';

  // Try to get the document if it previously existed in the database
  try {
    const document = (
      await client.getDocument({
        docId: exampleDocId,
        db: exampleDbName,
      })
    ).result;

    await client.deleteDocument({
      db: exampleDbName,
      docId: document._id, // `docId` is required for DELETE
      rev: document._rev, // `rev` is required for DELETE
    });
    console.log('You have deleted the document.');
  } catch (err) {
    if (err.code === 404) {
      console.log(
        `Cannot delete document because either "${exampleDbName}" database or the "example" ` +
          `document was not found.`
      );
    }
  }
};

if (require.main === module) {
  deleteDoc();
}

You have deleted the document.

Further code examples

For a complete list of code examples, see the examples directory.

Error handling

For sample code on handling errors, see Cloudant API docs.

Raw IO

For endpoints that read or write document content it is possible to bypass usage of the built-in interface with byte streams.

Depending on the specific SDK operation it may be possible to:

• accept a user-provided byte stream to send to the server as a request body
• return a byte stream of the server response body to the user

Request byte stream can be supplied for NodeJS.ReadableStream or Buffer type parameters . For these cases you can pass this byte stream directly to the HTTP request body.

Response byte stream is supported in functions with the suffix of AsStream. The returned byte stream allows the response body to be consumed without triggering JSON unmarshalling that is typically performed by the SDK.

The update document section contains examples for both request and response byte stream cases.

The API reference contains further examples of using byte streams. They are titled "Example request as stream" and are initially collapsed. Expand them to see examples of:

• Byte requests:

  • Bulk modify multiple documents in a database

• Byte responses:

  • Query a list of all documents in a database
  • Query the database document changes feed

Further resources

• Cloudant API docs: API reference including usage examples for Cloudant Node.js SDK API.
• TypeDoc: Cloudant Node.js SDK API Documentation.
• Cloudant docs: The official documentation page for Cloudant.
• Cloudant blog: Many useful articles about how to optimize Cloudant for common problems.

Browser usage

You can use the SDK directly from JavaScript running in a browser if:

• Polyfills for required Node.js system modules are available.
• The server configuration allows cross-origin resource sharing (CORS).

Polyfills

Use either:

• A bundler that includes polyfills for Node.js system modules in the browser.
• Or a Node.js compatible browser-based runtime.

The Node.js system modules required are:

• assert
• buffer
• crypto
• fs
• http
• https
• os
• path
• process
• querystring
• stream
• timers
• url
• util
• vm
• zlib

Additionally the SDK or its dependencies need to be able to resolve the globals:

• Buffer
• process
• Readable
• setImmediate and setTimeout

Environment variables:

• NODE_DEBUG (must be resolvable from the process.env even if it is unset)

It may be possible to omit some of these requirements for specific use cases.

CORS

To allow CORS requests from the SDK in the browser:

1. Configure the server with a CORS origin matching the URL protocol, host and port of the JavaScript application.
2. Either
   • Configure the server with a CORS headers allow list that includes the default headers plus the SDK's extra headers:
     • user-agent
     • x-ibmcloud-sdk-analytics
     • content-encoding (unless SDK request body compression is disabled)
   • Or configure the SDK to remove the extra headers from requests, for example:

     // Set a request interceptor to remove the headers from the requests
     service.getHttpClient().interceptors.request.use(requestConfig => {
     delete requestConfig.headers['User-Agent']
     delete requestConfig.headers['X-IBMCloud-SDK-Analytics']
     return requestConfig;
     });
     // Disable request body compression
     service.setEnableGzipCompression(false);
     

Changes feed follower (beta)

Introduction

The SDK provides a changes feed follower utility (currently beta). This helper utility connects to the _changes endpoint and returns the individual change items. It removes some of the complexity of using the _changes endpoint by setting some options automatically and providing error suppression and retries.

Tip: the changes feed often does not meet user expectations or assumptions.

Consult the Cloudant changes feed FAQ to get a better understanding of the limitations and suitable use-cases before using the changes feed in your application.

Modes of operation

There are two modes of operation:

• Start mode
  • Fetches the changes from the supplied since sequence (by default the feed will start from now).
  • Fetches all available changes and then continues listening for new changes indefinitely unless encountering an end condition.
  • An example use case for this mode is event driven workloads.
• Start one-off mode
  • Fetches the changes from the supplied since sequence (by default the feed will start from the beginning).
  • Fetches all available changes and then stops when either there are no further changes pending or encountering an end condition.
  • An example use case for this mode is ETL style workloads.

Configuring the changes follower

The SDK's model of changes feed options is also used to configure the follower. However, a subset of the options are invalid as they are configured internally by the implementation. Supplying these options when instantiating the follower causes an error. The invalid options are:

• descending
• feed
• heartbeat
• lastEventId - use since instead
• timeout
• Only the value of _selector is permitted for the filter option. This restriction is because selector based filters perform better than JavaScript backed filters. Configuring a non-selector based filter will cause the follower to error.

Note that the limit parameter will terminate the follower at the given number of changes in either operating mode.

The changes follower requires the client to have HTTP timeouts of at least 1 minute and will error during instantiation if it is insufficient. The default client configuration has sufficiently long timeouts.

For use-cases where these configuration limitations are deemed too restrictive then it is recommended to write code to use the SDK's POST _changes API instead of the follower.

Error suppression

By default, the changes follower will suppress transient errors indefinitely and attempt to run to completion or listen forever as dictated by the operating mode. For applications where that is not desirable an optional error tolerance duration may be specified to control the time since the last successful response that transient errors will be suppressed. This can be used, for example, by applications as a grace period before reporting an error and requiring intervention.

There are some additional points to consider for error suppression:

• Errors considered terminal, for example, the database not existing or invalid credentials are never suppressed and will error immediately.
• The error suppression duration is not guaranteed to fire immediately after lapsing and should be considered a minimum suppression time.
• The changes follower will back-off between retries and as such may remain paused for a short while after the transient errors have resolved.
• If the underlying SDK client used to initialize the follower also has retries configured then errors could be suppressed for significantly longer than the follower's configured error tolerance duration depending on the configuration options.

Follower operation

For both modes:

• The end conditions are:
  • A terminal error (HTTP codes 400, 401, 403 404).
  • Transient errors occur for longer than the error tolerance duration. Transient errors are all other HTTP status codes and connection errors.
  • The number of changes received reaches the configured limit.
  • The feed is terminated early by calling stop.

As is true for the _changes endpoint change items have at least once delivery and an individual item may be received multiple times. When using the follower change items may be repeated even within a limited number of changes (i.e. using the limit option) this is a minor difference from using limit on the HTTP native API.

The follower is not optimized for some use cases and it is not recommended to use it in cases where:

• Setting include_docs and larger document sizes (for example > 10 kiB).
• The volume of changes is very high (if the rate of changes in the database exceeds the follower's rate of pulling them it will never catch-up).

In these cases use-case specific control over the number of change requests made and the content size of the responses may be achieved by using the SDK's POST _changes API.

Checkpointing

The changes follower does not checkpoint since it has no information about whether a change item has been processed by the consuming application after being received. It is the application developer's responsibility to store the sequence IDs to have appropriate checkpoints and to re-initialize the follower with the required since value after, for example, the application restarts.

The frequency and conditions for checkpointing are application specific and some applications may be tolerant of dropped changes. This section is intended only to provide general guidance on how to avoid missing changes.

To guarantee processing of all changes the sequence ID from a change item must not be persisted until after the processing of the change item by the application has completed. As indicated previously change items are delivered at least once so application code must be able to handle repeated changes already and it is preferable to restart from an older since value and receive changes again than risk missing them.

The sequence IDs are available on each change item by default, but may be omitted from some change items when using the seq_interval configuration option. Infrequent sequence IDs may improve performance by reducing the amount of data that needs to be transferred, but the trade-off is that more changes will be repeated if it is necessary to resume the changes follower.

Extreme care should be taken with persisting sequences if choosing to process change items in parallel as there is a considerable risk of missing changes on a restart if the sequence is recorded out of order.

Code examples

Initializing a changes follower

import { ChangesFollower, CloudantV1 } from '@ibm-cloud/cloudant';
import { PostChangesParams } from '@ibm-cloud/cloudant/cloudant/v1';

const client = CloudantV1.newInstance({});
const changesParams: PostChangesParams = {
  db: 'example', // Required: the database name.
  limit: 100, // Optional: return only 100 changes (including duplicates).
  since: '3-g1AG3...' // Optional: start from this sequence ID (e.g. with a value read from persistent storage).
};
const errorTolerance: number = 10000; // 10 second duration to suppress transient errors
const changesFollower: ChangesFollower = new ChangesFollower(
  client, // Required: the Cloudant service client instance.
  changesParams, // Required: changes feed configuration options dict.
  10000 // Optional: suppress transient errors for at least 10 seconds before terminating.
);

import { ChangesFollower, CloudantV1 } from '@ibm-cloud/cloudant';

const client = CloudantV1.newInstance();
const changesParams = {
  db: 'example', // Required: the database name.
  limit: 100, // Optional: return only 100 changes (including duplicates).
  since: '3-g1AG3...' // Optional: start from this sequence ID (e.g. with a value read from persistent storage).
};
const changesFollower = new ChangesFollower(
  client, // Required: the Cloudant service client instance.
  changesParams, // Required: changes feed configuration options dict.
  10000 // Optional: suppress transient errors for at least 10 seconds before terminating.
);

Starting the changes follower

Start mode for continuous listening

import { ChangesFollower, CloudantV1, Stream } from '@ibm-cloud/cloudant';
import { ChangesResultItem, PostChangesParams } from '@ibm-cloud/cloudant/cloudant/v1';

const client = CloudantV1.newInstance({});
const changesParams: PostChangesParams = {
  db: 'example'
};
const changesFollower: ChangesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream: Stream<ChangesResultItem> = changesFollower.start();
// Create for-async-loop or pipeline to begin the flow of changes
// e.g. pipeline(changesItemsStream, destinationStream).then(() => { ... }).catch((err) => { ... });

import { ChangesFollower, CloudantV1 } from '@ibm-cloud/cloudant';

const client = CloudantV1.newInstance();
const changesParams = {
  db: 'example'
};
const changesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream = changesFollower.start();
// Create for-async-loop or pipeline to begin the flow of changes
// e.g. pipeline(changesItemsStream, destinationStream).then(() => { ... }).catch((err) => { ... });

Start mode for one-off fetching

import { ChangesFollower, CloudantV1, Stream } from '@ibm-cloud/cloudant';
import { ChangesResultItem, PostChangesParams } from '@ibm-cloud/cloudant/cloudant/v1';

const client = CloudantV1.newInstance({});
const changesParams: PostChangesParams = {
  db: 'example'
};
const changesFollower: ChangesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream: Stream<ChangesResultItem> = changesFollower.startOneOff();
// Create for-async-loop or pipeline to begin the flow of changes
// e.g. pipeline(changesItemsStream, destinationStream).then(() => { ... }).catch((err) => { ... });

import { ChangesFollower, CloudantV1 } from '@ibm-cloud/cloudant';

const client = CloudantV1.newInstance();
const changesParams = {
  db: 'example'
};
const changesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream = changesFollower.startOneOff();
// Create for-async-loop or pipeline to begin the flow of changes
// e.g. pipeline(changesItemsStream, destinationStream).then(() => { ... }).catch((err) => { ... });

Processing changes

Process continuous changes

import { ChangesFollower, CloudantV1, Stream } from '@ibm-cloud/cloudant';
import { ChangesResultItem, PostChangesParams } from '@ibm-cloud/cloudant/cloudant/v1';
import { Writable } from 'node:stream';
import { pipeline } from 'node:stream/promises';

const client = CloudantV1.newInstance({});
// Start from a previously persisted seq
// Normally this would be read by the app from persistent storage
// e.g. previouslyPersistedSeq = yourAppPersistenceReadFunc()
const previouslyPersistedSeq = '3-g1AG3...';
const changesParams: PostChangesParams = {
  db: 'example',
  since: previouslyPersistedSeq
};
const changesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream: Stream<ChangesResultItem> = changesFollower.start();

const destinationStream = new Writable({
  objectMode: true,
  write(changesItem: CloudantV1.ChangesResultItem, _, callback) {
    // do something with change item
    console.log(changesItem.id);
    for (const change of changesItem.changes) {
      console.log(change.rev);
    }
    // when change item processing is complete app can store seq
    const seq = changesItem.seq;
    // write seq to persistent storage for use as since if required to resume later
    // e.g. yourAppPersistenceWriteFunc()
    callback();
  }
});

// A pipeline to keep processing changes until the follower is stopped or some other stop condition is reached
pipeline(changesItemsStream, destinationStream)
  .then(() => {
    console.log('Stopped');
  })
  .catch((err) => {
    console.log(err);
  });

import { ChangesFollower, CloudantV1 } from '@ibm-cloud/cloudant';
import { Writable } from 'node:stream';
import { pipeline } from 'node:stream/promises';

const client = CloudantV1.newInstance();
// Start from a previously persisted seq
// Normally this would be read by the app from persistent storage
// e.g. previouslyPersistedSeq = yourAppPersistenceReadFunc()
const previouslyPersistedSeq = '3-g1AG3...';
const changesParams = {
  db: 'example',
  since: previouslyPersistedSeq
};
const changesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream = changesFollower.start();

const destinationStream = new Writable({
  objectMode: true,
  write(changesItem, _, callback) {
    // do something with change item
    console.log(changesItem.id);
    for (const change of changesItem.changes) {
      console.log(change.rev);
    }
    // when change item processing is complete app can store seq
    const seq = changesItem.seq;
    // write seq to persistent storage for use as since if required to resume later
    // e.g. yourAppPersistenceWriteFunc()
    callback();
  }
});

// A pipeline to keep processing changes until the follower is stopped or some other stop condition is reached
pipeline(changesItemsStream, destinationStream)
  .then(() => {
    console.log('Stopped');
  })
  .catch((err) => {
    console.log(err);
  });

Process one-off changes

import { ChangesFollower, CloudantV1, Stream } from '@ibm-cloud/cloudant';
import { ChangesResultItem, PostChangesParams } from '@ibm-cloud/cloudant/cloudant/v1';
import { Writable } from 'node:stream';
import { pipeline } from 'node:stream/promises';

const client = CloudantV1.newInstance({});
// Start from a previously persisted seq
// Normally this would be read by the app from persistent storage
// e.g. previouslyPersistedSeq = yourAppPersistenceReadFunc()
const previouslyPersistedSeq = '3-g1AG3...';
const changesParams: PostChangesParams = {
  db: 'example',
  since: previouslyPersistedSeq
};
const changesFollower: ChangesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream: Stream<ChangesResultItem> = changesFollower.startOneOff();

const destinationStream = new Writable({
  objectMode: true,
  write(changesItem: CloudantV1.ChangesResultItem, _, callback) {
    // do something with change item
    console.log(changesItem.id);
    for (const change of changesItem.changes) {
      console.log(change.rev);
    }
    // when change item processing is complete app can store seq
    const seq = changesItem.seq;
    // write seq to persistent storage for use as since if required to resume later
    // e.g. yourAppPersistenceWriteFunc()
    callback();
  }
});

pipeline(changesItemsStream, destinationStream)
  .then(() => {
    console.log('All changes done');
  })
  .catch((err) => {
    console.log(err);
  });

// use for-async-loop feature for stream
/*
getChangesFromFollower(changesItemsStream);
async function getChangesFromFollower(changesItemsStream: Stream<CloudantV1.ChangesResultItem>) {
  for await (const changesItem of changesItemsStream) {
    // do something with change item
    // write seq to persistent storage for use as since
    console.log(changesItem.id);
    for (const change of changesItem.changes) {
      console.log(change.rev);
    }
    // when change item processing is complete app can store seq
    seq = changesItem.seq;
    // write seq to persistent storage for use as since if required to resume later
    // e.g. yourAppPersistenceWriteFunc();
  }
}
*/

import { ChangesFollower, CloudantV1 } from '@ibm-cloud/cloudant';
import { Writable } from 'node:stream';
import { pipeline } from 'node:stream/promises';

const client = CloudantV1.newInstance();
// Start from a previously persisted seq
// Normally this would be read by the app from persistent storage
// e.g. previouslyPersistedSeq = yourAppPersistenceReadFunc()
const previouslyPersistedSeq = '3-g1AG3...';
const changesParams = {
  db: 'example',
  since: previouslyPersistedSeq
};
const changesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream = changesFollower.startOneOff();

const destinationStream = new Writable({
  objectMode: true,
  write(changesItem, _, callback) {
    // do something with change item
    console.log(changesItem.id);
    for (const change of changesItem.changes) {
      console.log(change.rev);
    }
    // when change item processing is complete app can store seq
    const seq = changesItem.seq;
    // write seq to persistent storage for use as since if required to resume later
    // e.g. yourAppPersistenceWriteFunc()
    callback();
  }
});

pipeline(changesItemsStream, destinationStream)
  .then(() => {
    console.log('All changes done');
  })
  .catch((err) => {
    console.log(err);
  });

// use for-async-loop feature for stream
/*
getChangesFromFollower(changesItemsStream);
async function getChangesFromFollower(changesItemsStream) {
  for await (const changesItem of changesItemsStream) {
    // do something with change item
    // write seq to persistent storage for use as since
    console.log(changesItem.id);
    for (const change of changesItem.changes) {
      console.log(change.rev);
    }
    // when change item processing is complete app can store seq
    seq = changesItem.seq;
    // write seq to persistent storage for use as since if required to resume later
    // e.g. yourAppPersistenceWriteFunc();
  }
}
*/

Stopping the changes follower

import { ChangesFollower, CloudantV1, Stream } from '@ibm-cloud/cloudant';
import { ChangesResultItem, PostChangesParams } from '@ibm-cloud/cloudant/cloudant/v1';
import { Writable } from 'node:stream';
import { pipeline } from 'node:stream/promises';

const client = CloudantV1.newInstance({});
const changesParams: PostChangesParams = {
  db: 'example'
};
const changesFollower: ChangesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream: Stream<ChangesResultItem> = changesFollower.start();

const destinationStream = new Writable({
  objectMode: true,
  write(changesItem: CloudantV1.ChangesResultItem, _, callback) {
    // Option 1: call stop after some condition
    // Note that at least one item
    // must be returned to reach to this point.
    // Additional changes may be processed before the iterator stops.
    changesFollower.stop();
    callback();
  }
});

pipeline(changesItemsStream, destinationStream)
  .then(() => {
    console.log('Stopped');
  })
  .catch((err) => {
    console.log(err);
  });

// Option 2: call stop method when you want to end the continuous loop from
// outside the pipeline.
// Normally the call would be made from some other application function
// executing later.
// For example, stop the changesFollower after 1 minute of listening for changes
setTimeout(() => {
  changesFollower.stop();
}, 60000);

import { ChangesFollower, CloudantV1 } from '@ibm-cloud/cloudant';
import { Writable } from 'node:stream';
import { pipeline } from 'node:stream/promises';

const client = CloudantV1.newInstance();
const changesParams = {
  db: 'example'
};
const changesFollower = new ChangesFollower(client, changesParams);
const changesItemsStream = changesFollower.start();

const destinationStream = new Writable({
  objectMode: true,
  write(changesItem, _, callback) {
    // Option 1: call stop after some condition
    // Note that at least one item
    // must be returned to reach to this point.
    // Additional changes may be processed before the iterator stops.
    changesFollower.stop();
    callback();
  }
});

pipeline(changesItemsStream, destinationStream)
  .then(() =>{
    console.log('Stopped');
  })
  .catch((err) => {
    console.log(err);
  });

// Option 2: call stop method when you want to end the continuous loop from
// outside the pipeline.
// Normally the call would be made from some other application function
// executing later.
// For example, stop the changesFollower after 1 minute of listening for changes
setTimeout(() => {
  changesFollower.stop();
}, 60000);

Questions

If you are having difficulties using this SDK or have a question about the IBM Cloud services, ask a question on Stack Overflow.

Issues

If you encounter an issue with the project, you are welcome to submit a bug report.

Before you submit a bug report, search for similar issues and review the KNOWN_ISSUES file to verify that your issue hasn't been reported yet.

Please consult the security policy before opening security related issues.

Versioning and LTS support

This SDK follows semantic versioning with respect to the definition of user facing APIs. This means under some circumstances breaking changes may occur within a major or minor version of the SDK related to changes in supported language platforms.

The SDK is supported on the available LTS releases of the language platform. The LTS language versions are listed in the prerequisites:

• LTS versions currently supported by the SDK
• LTS versions for this release of the SDK

Incompatible changes from new language versions are not added to the SDK until they are available in the minimum supported language version.

When language LTS versions move out of support the following will happen:

• Existing SDK releases will continue to run on obsolete language versions, but will no longer be supported.
• The minimum language version supported by the SDK will be updated to the next available LTS.
• New language features may be added in subsequent SDK releases that will cause breaking changes if the new releases of the SDK are used with older, now unsupported, language levels.

Open source at IBM

Find more open source projects on the IBM GitHub page.

Contributing

For more information, see CONTRIBUTING.

License

This SDK is released under the Apache 2.0 license. To read the full text of the license, see LICENSE.