cloudant-go-sdk

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Published: Jul 9, 2024 License: Apache-2.0

README

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IBM Cloudant Go SDK Version 0.8.0

IBM Cloudant Go 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.

Table of Contents

Overview

The IBM Cloudant Go SDK allows developers to programmatically interact with IBM Cloudant with the help of the cloudantv1 package.

Features

The purpose of this Go 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 Go SDK in your project:

  • Supported by IBM Cloudant.
  • Server compatibility with:
  • 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)
  • HTTP2 support for higher performance connections to IBM Cloudant.
  • Perform requests synchronously.
  • Safe for concurrent use by multiple goroutines.
  • Transparently compresses request and response bodies.

Prerequisites

  • A Cloudant service instance or a CouchDB server.
  • Go version 1.21 or 1.22.

Installation

The current version of this SDK: 0.8.0

There are a few different ways to download and add the Cloudant Go SDK project for use by your Go application:

go get command

Use this command to download and add the SDK to allow your Go application to use it:

go get -u github.com/IBM/cloudant-go-sdk/cloudantv1@v0.8.0
Go modules

If your application is using Go modules, you can add a suitable import to your Go application, like this:

import (
  "github.com/IBM/cloudant-go-sdk/cloudantv1"
)

then run go mod tidy to download and install the latest version if the dependency is missing. This command will also update your Go application's go.mod file.

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)
  • Username and password credentials (can be used with authentication types COUCHDB_SESSION and BASIC)

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.

Authentication type Recommended for AUTH_TYPE Description
IAM Trusted Profiles compute resource (container) Cloudant
(SDK running in IBM Cloud IKS)
CONTAINER Obtains a compute resource (CR) token from the container.
Exchanges the CR token for an IAM access_token.
Adds an Authorization: Bearer <access_token> header to each HTTP request.
Automatically renews the access token when needed.
IAM Trusted Profiles compute resource (VPC) Cloudant
(SDK running in IBM Cloud VPC)
VPC Obtains an identity token from the VPC instance metadata.
Exchanges the identity token for an IAM access_token.
Adds an Authorization: Bearer <access_token> header to each HTTP request.
Automatically renews the access token when needed.
IAM API key Cloudant IAM Exchanges an IAM API key for an IAM access_token.
Adds an Authorization: Bearer <access_token> header to each HTTP request.
Automatically renews the access token when needed.
Session cookie Cloudant
(legacy credentials & instances without IAM)

Apache CouchDB
COUCHDB_SESSION Exchanges credentials with /_session endpoint to retrieve a cookie.
Adds Cookie header and content to each HTTP request.
Automatically renews session when needed.
Bearer token Apache CouchDB
(using JWT authentication)
BEARERTOKEN Adds an Authorization: Bearer <token> to each HTTP request.
No token management or renewal.
Also compatible with IAM access tokens managed independently of the SDK.
Basic Apache CouchDB
(if cookies are not enabled)
BASIC Adds an Authorization: Basic <encoded username and password> header to each HTTP request.
None - NOAUTH Note that this authentication type only works for operations against a database allowing access for unauthenticated users.

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.

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 Go 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

A 6m request timeout, which includes a 30s connect timeout, is set by default. Note that this also affects changes feed requests, regardless of a timeout set on PostChangesOptions. 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.

package main

import (
	"encoding/json"
	"fmt"

	"github.com/IBM/cloudant-go-sdk/cloudantv1"
)

func main() {
	// 1. Create a client with `CLOUDANT` default service name =============
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	// 2. Create a database ================================================
	exampleDbName := "orders"

	putDatabaseResult, putDatabaseResponse, err := client.PutDatabase(
		client.NewPutDatabaseOptions(exampleDbName),
	)
	if err != nil {
		if putDatabaseResponse.StatusCode == 412 {
			fmt.Printf("Cannot create \"%s\" database, it already exists.\n",
				exampleDbName)
		} else {
			panic(err)
		}
	}

	if putDatabaseResult != nil && *putDatabaseResult.Ok {
		fmt.Printf("\"%s\" database created.\n", exampleDbName)
	}

	// 3. Create a document ================================================
	// Create a document object with "example" id
	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.
	exampleDocument := cloudantv1.Document{
		ID: &exampleDocID,
	}

	// Add "name" and "joined" fields to the document
	exampleDocument.SetProperty("name", "Bob Smith")
	exampleDocument.SetProperty("joined", "2019-01-24T10:42:59.000Z")

	// Save the document in the database with "PostDocument" function
	createDocumentOptions := client.NewPostDocumentOptions(
		exampleDbName,
	).SetDocument(&exampleDocument)

	createDocumentResponse, _, err := client.PostDocument(createDocumentOptions)

	// =====================================================================
	// Note: saving the document can also be done with the "PutDocument"
	// function. In this case docID is required for a CREATE operation:
	/*
		createDocumentOptions := client.NewPutDocumentOptions(
			exampleDbName,
			exampleDocID,
		).SetDocument(&exampleDocument)

		createDocumentResponse, _, err := client.PutDocument(createDocumentOptions)
	*/
	// =====================================================================

	if err != nil {
		panic(err)
	}

	// Keeping track of the revision number of the document object
	// is necessary for further UPDATE/DELETE operations:
	exampleDocument.Rev = createDocumentResponse.Rev

	// Print out the document content
	exampleDocumentContent, _ := json.MarshalIndent(exampleDocument, "", "  ")
	fmt.Printf("You have created the document:\n%s\n", string(exampleDocumentContent))
}

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

"orders" database created.
You have created the document:
{
  "_id": "example",
  "_rev": "1-1b403633540686aa32d013fda9041a5d",
  "joined": "2019-01-24T10:42:99.000Z",
  "name": "Bob Smith"
}
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."

Gather database information example
package main

import (
	"encoding/json"
	"fmt"

	"github.com/IBM/cloudant-go-sdk/cloudantv1"
)

func main() {
	// 1. Create a client with `CLOUDANT` default service name ============
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}
	// 2. Get server information ===========================================
	serverInformationResult, _, err := client.GetServerInformation(
		client.NewGetServerInformationOptions(),
	)
	if err != nil {
		panic(err)
	}
	fmt.Printf("Server Version: %s\n", *serverInformationResult.Version)
	// 3. Get database information for "orders" ==========================
	dbName := "orders"
	databaseInformationResult, _, err := client.GetDatabaseInformation(
		client.NewGetDatabaseInformationOptions(
			dbName,
		),
	)
	if err != nil {
		panic(err)
	}
	// 4. Show document count in database ==================================
	fmt.Printf("Document count in \"%s\" database is %d.\n",
		*databaseInformationResult.DbName,
		*databaseInformationResult.DocCount)
	// 5. Get "example" document out of the database by document id ============
	documentExampleResult, _, err := client.GetDocument(
		client.NewGetDocumentOptions(
			dbName,
			"example",
		),
	)
	if err != nil {
		panic(err)
	}
	// 6. Print out the Document content ===================================
	exampleBuffer, _ := json.MarshalIndent(documentExampleResult, "", "  ")
	fmt.Println(string(exampleBuffer))
}
When you run the code, you see a result similar to the following output.
Server Version: 2.1.1
Document count in "orders" database is 1.
{
  "_id": "example",
  "_rev": "1-1b403633540686aa32d013fda9041a5d",
  "name": "Bob Smith",
  "joined": "2019-01-24T10:42:99.000Z"
}
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."

Update code example
package main

import (
	"encoding/json"
	"fmt"

	"github.com/IBM/cloudant-go-sdk/cloudantv1"
)

func main() {
	// 1. Create a client with `CLOUDANT` default service name =============
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	// 2. Update the document ==============================================
	exampleDbName := "orders"
	exampleDocID := "example"

	// Get the document if it previously existed in the database
	document, getDocumentResponse, err := client.GetDocument(
		client.NewGetDocumentOptions(
			exampleDbName,
			exampleDocID,
		),
	)

	// =====================================================================
	// Note: for response byte stream use:
	/*
		documentAsByteStream, getDocumentResponse, err := client.GetDocumentAsStream(
			client.NewGetDocumentOptions(
				exampleDbName,
				exampleDocID,
			),
		)
	*/
	// =====================================================================

	if err != nil {
		if getDocumentResponse.StatusCode == 404 {
			fmt.Printf("Cannot update document because "+
				"either \"%s\"  database or \"%s\" document was not found.\n",
				exampleDbName,
				exampleDocID)
		} else {
			panic(err)
		}
	}

	if document != nil {
		// Make some modification in the document content
		// Add Bob Smith's address to the document
		document.SetProperty("address", "19 Front Street, Darlington, DL5 1TY")
		// Remove the joined property from document object
		delete(document.GetProperties(), "joined")

		// Update the document in the database
		updateDocumentOptions := client.NewPostDocumentOptions(
			exampleDbName,
		).SetDocument(document)

		// =================================================================
		// Note: for request byte stream use:
		/*
			postDocumentOption := client.NewPostDocumentOptions(
				exampleDbName,
			).SetBody(documentAsByteStream)
		*/
		// =================================================================

		updateDocumentResponse, _, err := client.PostDocument(
			updateDocumentOptions,
		)

		// =================================================================
		// Note: 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 too:
		/*
			updateDocumentOptions := client.NewPutDocumentOptions(
				exampleDbName,
				core.StringNilMapper(document.ID), // docID is a required parameter
			).SetDocument(document) // Rev in the document object CAN replace below SetRev

			updateDocumentOptions.SetRev(core.StringNilMapper(document.Rev))

			updateDocumentResponse, _, err := client.PutDocument(
				updateDocumentOptions,
			)
		*/
		// =================================================================

		if err != nil {
			panic(err)
		}

		// Keeping track of the latest revision number of the document object
		// is necessary for further UPDATE/DELETE operations:
		document.Rev = updateDocumentResponse.Rev

		// Print out the new document content
		documentContent, _ := json.MarshalIndent(document, "", "  ")
		fmt.Printf("You have updated the document:\n%s\n", string(documentContent))
	}
}
When you run the code, you see a result similar to the following output.
You have updated the document:
{
  "_id": "example",
  "_rev": "2-4e2178e85cffb32d38ba4e451f6ca376",
  "address": "19 Front Street, Darlington, DL5 1TY",
  "name": "Bob Smith"
}
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."

Delete code example
package main

import (
	"fmt"

	"github.com/IBM/cloudant-go-sdk/cloudantv1"
)

func main() {

	// 1. Create a client with `CLOUDANT` default service name =============
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	// 2. Delete the document ==============================================
	exampleDbName := "orders"
	exampleDocID := "example"

	// 2.1. Get the document if it previously existed in the database
	document, getDocumentResponse, err := client.GetDocument(
		client.NewGetDocumentOptions(
			exampleDbName,
			exampleDocID,
		),
	)
	if err != nil {
		if getDocumentResponse.StatusCode == 404 {
			fmt.Printf("Cannot delete document because "+
				"either \"%s\" database or \"%s\" document was not found.\n",
				exampleDbName,
				exampleDocID)
		} else {
			panic(err)
		}
	}
	// 2.2. Use its latest revision to delete
	if document != nil {
		deleteDocumentResult, _, err := client.DeleteDocument(
			client.NewDeleteDocumentOptions(
				exampleDbName,
				*document.ID, // docID is required for DELETE
			).SetRev(*document.Rev), // Rev is required for DELETE
		)
		if err != nil {
			panic(err)
		}

		if *deleteDocumentResult.Ok {
			fmt.Println("You have deleted the document.")
		}
	}
}
When you run the code, you see the following output.
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 struct 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 method options that have a Body property. 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:

Further resources
  • Cloudant API docs: API reference including usage examples for Cloudant Go SDK API.
  • Godoc: Cloudant Go SDK API Documentation.
  • Cloudant docs: The official documentation page for Cloudant.
  • Cloudant blog: Many useful articles about how to optimize Cloudant for common problems.
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
package main

import (
	"time"

	"github.com/IBM/cloudant-go-sdk/cloudantv1"
	"github.com/IBM/cloudant-go-sdk/features"
)

func main() {
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	// Required: the database name.
	postChangesOptions := client.NewPostChangesOptions("example")

	// Optional: return only 100 changes (including duplicates).
	postChangesOptions.SetLimit(100)

	// Optional: start from this sequence ID (e.g. with a value read from persistent storage).
	postChangesOptions.SetSince("3-g1AG3...")

	// Required: the Cloudant service client instance and an instance of PostChangesOptions
	follower, err := features.NewChangesFollower(client, postChangesOptions)
	if err != nil {
		panic(err)
	}

	// Optional: suppress transient errors for at least 10 seconds before terminating.
	err = follower.SetErrorTolerance(10 * time.Second)
	if err != nil {
		panic(err)
	}
}
Starting the changes follower
Start mode for continuous listening
package main

import (
	"github.com/IBM/cloudant-go-sdk/cloudantv1"
	"github.com/IBM/cloudant-go-sdk/features"
)

func main() {
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	postChangesOptions := client.NewPostChangesOptions("example")

	follower, err := features.NewChangesFollower(client, postChangesOptions)
	if err != nil {
		panic(err)
	}

	changesCh, err := follower.Start()
	if err != nil {
		panic(err)
	}

	// Note: changesCh channel will not do anything until it is read from.
	// Create a range loop to iterate over the flow of the changes items
}
Start mode for one-off fetching
package main

import (
	"github.com/IBM/cloudant-go-sdk/cloudantv1"
	"github.com/IBM/cloudant-go-sdk/features"
)

func main() {
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	postChangesOptions := client.NewPostChangesOptions("example")

	follower, err := features.NewChangesFollower(client, postChangesOptions)
	if err != nil {
		panic(err)
	}

	changesCh, err = follower.StartOneOff()
	if err != nil {
		panic(err)
	}

	// Note: the returned channel will not do anything until it is read
	// Create a range loop to iterate over the flow of the change items
}
Processing changes
Process continuous changes
package main

import (
	"fmt"

	"github.com/IBM/cloudant-go-sdk/cloudantv1"
	"github.com/IBM/cloudant-go-sdk/features"
)

func main() {
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	postChangesOptions := client.NewPostChangesOptions("example")

	// Start from a previously persisted seq
	// Normally this would be read by the app from persistent storage
	// e.g. prevSeq = yourAppPersistenceReadFunc()
	prevSeq := "3-g1AG3..."
	postChangesOptions.SetSince(prevSeq)

	follower, err := features.NewChangesFollower(client, postChangesOptions)
	if err != nil {
		panic(err)
	}

	changesCh, err := follower.Start()
	if err != nil {
		panic(err)
	}

	for changesItem := range changesCh {
		// changes item returns an error on failed requests
		item, err := changesItem.Item()
		if err != nil {
			panic(err)
		}

		// do something with changes
		fmt.Printf("%s\n", *item.ID)
		for _, change := range item.Changes {
			fmt.Printf("%s\n", *change.Rev)
		}

		// when change item processing is complete app can store seq
		seq := *item.Seq
		// write seq to persistent storage for use as since
		// if required to resume later, e.g. yourAppPersistenceWriteFunc(seq)
		// keep processing changes until the application is terminated
		// or some other stop condition is reached
	}

	// Note: the returned channel continues to listen for changes
	// indefinitely. In other words iterating it is blocking,
	// code here will be unreachable until break from the range
	// or another stop condition is reached.
	// For long running followers careful consideration
	// should be made of where to call stop on the follower.
}
Process one-off changes
package main

import (
	"fmt"

	"github.com/IBM/cloudant-go-sdk/cloudantv1"
	"github.com/IBM/cloudant-go-sdk/features"
)

func main() {
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	postChangesOptions := client.NewPostChangesOptions("example")

	// Start from a previously persisted seq
	// Normally this would be read by the app from persistent storage
	// e.g. prevSeq = yourAppPersistenceReadFunc()
	prevSeq := "3-g1AG3..."
	postChangesOptions.SetSince(prevSeq)

	follower, err := features.NewChangesFollower(client, postChangesOptions)
	if err != nil {
		panic(err)
	}

	changesCh, err := follower.StartOneOff()
	if err != nil {
		panic(err)
	}

	for changesItem := range changesCh {
		// changes item structure returns an error on failed requests
		item, err := changesItem.Item()
		if err != nil {
			panic(err)
		}

		// do something with changes
		fmt.Printf("%s\n", *item.ID)
		for _, change := range item.Changes {
			fmt.Printf("%s\n", *change.Rev)
		}

		// when change item processing is complete app can store seq
		seq := *item.Seq
		// write seq to persistent storage for use as since if required
		// to resume later, e.g. yourAppPersistenceWriteFunc(seq)
	}

	// Note: iterating the returned channel above is blocking, code here
	// will be unreachable until all changes are processed
	// or another stop condition is reached.
}
Stopping the changes follower
package main

import (
	"context"

	"github.com/IBM/cloudant-go-sdk/cloudantv1"
	"github.com/IBM/cloudant-go-sdk/features"
)

func main() {
	client, err := cloudantv1.NewCloudantV1UsingExternalConfig(
		&cloudantv1.CloudantV1Options{},
	)
	if err != nil {
		panic(err)
	}

	postChangesOptions := client.NewPostChangesOptions("example")

	ctx, cancel := context.WithCancel(context.Background())
	// Option 1: call cancel function when ChangesFollower created
	// with a cancellable context.
	// Note that this is a good practice to always call cancel function,
	// e.g. in defer to prevent possible goroutine leak.
	defer cancel()
	follower, err := features.NewChangesFollowerWithContext(ctx, client, postChangesOptions)
	if err != nil {
		panic(err)
	}

	changesCh, err := follower.Start()
	if err != nil {
		panic(err)
	}

	for changesItem := range changesCh {
		// changes item structure returns an error on failed requests
		if changesItem.Error != nil {
			panic(changesItem.Error)
		}

		// Option 2: call stop after some condition
		// Note that at least one item must be returned from the channel
		// to reach this point. Additional changes may be processed
		// before the channel quits.
		follower.Stop()
	}

	// Option 3: call stop method when you want to end the continuous loop from
	// outside the channel. For example, you've put the changes follower in a
	// goroutine and need to call stop on the main goroutine.
	// Note: in this context the call must be made from a different
	// goroutine because code immediately following the range is unreachable
	// until the channel has quit.
	follower.Stop()
}

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:

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.

Directories

Path Synopsis
Package cloudantv1 : Operations and models for the CloudantV1 service
Package cloudantv1 : Operations and models for the CloudantV1 service
test

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