Ably Go

Ably is the platform that powers synchronized digital experiences in realtime. Whether attending an event in a virtual venue, receiving realtime financial information, or monitoring live car performance data – consumers simply expect realtime digital experiences as standard. Ably provides a suite of APIs to build, extend, and deliver powerful digital experiences in realtime for more than 250 million devices across 80 countries each month. Organizations like Bloomberg, HubSpot, Verizon, and Hopin depend on Ably’s platform to offload the growing complexity of business-critical realtime data synchronization at global scale. For more information, see the Ably documentation.

Overview

This is a Go client library for Ably. Supported features and known limitations are documented here.

Installation

~ $ go get -u github.com/ably/ably-go/ably

See Requirements

Usage

Using the Realtime API

Creating a client

client, err := ably.NewRealtime(ably.WithKey("xxx:xxx"))
if err != nil {
        panic(err)
}
channel := client.Channels.Get("test")

Subscribing to events

You may monitor events on connections and channels.

client, err = ably.NewRealtime(
ably.WithKey("xxx:xxx"),
ably.WithAutoConnect(false), // Set this option to avoid missing state changes.
)
if err != nil {
        panic(err)
}
// Set up connection events handler.
client.Connection.OnAll(func(change ably.ConnectionStateChange) {
        fmt.Printf("Connection event: %s state=%s reason=%s", change.Event, change.Current, change.Reason)
})
// Then connect.
client.Connect()
channel = client.Channels.Get("test")
channel.OnAll(func(change ably.ChannelStateChange) {
        fmt.Printf("Channel event event: %s channel=%s state=%s reason=%s", channel.Name, change.Event, change.Current, change.Reason)
})

Subscribing to a channel for all messages

unsubscribe, err := channel.SubscribeAll(ctx, func(msg *ably.Message) {
        fmt.Printf("Received message: name=%s data=%v\n", msg.Name, msg.Data)
})
if err != nil {
        panic(err)
}

Subscribing to a channel for EventName1 and EventName2 message names

unsubscribe1, err := channel.Subscribe(ctx, "EventName1", func(msg *ably.Message) {
        fmt.Printf("Received message: name=%s data=%v\n", msg.Name, msg.Data)
})
if err != nil {
        panic(err)
}
unsubscribe2, err := channel.Subscribe(ctx, "EventName2", func(msg *ably.Message) {
        fmt.Printf("Received message: name=%s data=%v\n", msg.Name, msg.Data)
})
if err != nil {
        panic(err)
}

Publishing to a channel

err = channel.Publish(ctx, "EventName1", "EventData1")
if err != nil {
        panic(err)
}

Publish will block until either the publish is acknowledged or failed to deliver.

Alternatively you can use PublishAsync which does not block:

channel.PublishAsync("EventName1", "EventData11", func(err error) {
	if err != nil {
		fmt.Println("failed to publish", err)
	} else {
		fmt.Println("publish ok")
	}
})

Note the onAck callback must not block as it would block the internal client.

Handling errors

Errors returned by this library may have an underlying *ErrorInfo type.

See Ably documentation for ErrorInfo.

badClient, err := ably.NewRealtime(ably.WithKey("invalid:key"))
if err != nil {
        panic(err)
}
err = badClient.Channels.Get("test").Publish(ctx, "event", "data")
if errInfo := (*ably.ErrorInfo)(nil); errors.As(err, &errInfo) {
        fmt.Printf("Error publishing message: code=%v status=%v cause=%v", errInfo.Code, errInfo.StatusCode, errInfo.Cause)
} else if err != nil {
        panic(err)
}

Announcing presence on a channel

err = channel.Presence.Enter(ctx, "presence data")
if err != nil {
        panic(err)
}

Announcing presence on a channel on behalf of other client

err = channel.Presence.EnterClient(ctx, "clientID", "presence data")
if err != nil {
        panic(err)
}

Updating and leaving presence

// Update also has an UpdateClient variant.
err = channel.Presence.Update(ctx, "new presence data")
if err != nil {
        panic(err)
}
// Leave also has an LeaveClient variant.
err = channel.Presence.Leave(ctx, "last presence data")
if err != nil {
        panic(err)
}

Getting all clients present on a channel

clients, err := channel.Presence.Get(ctx)
if err != nil {
        panic(err)
}
for _, client := range clients {
        fmt.Println("Present client:", client)
}

Subscribing to all presence messages

unsubscribe, err = channel.Presence.SubscribeAll(ctx, func(msg *ably.PresenceMessage) {
        fmt.Printf("Presence event: action=%v data=%v", msg.Action, msg.Data)
})
if err != nil {
        panic(err)
}

Subscribing to 'Enter' presence messages only

unsubscribe, err = channel.Presence.Subscribe(ctx, ably.PresenceActionEnter, func(msg *ably.PresenceMessage) {
        fmt.Printf("Presence event: action=%v data=%v", msg.Action, msg.Data)
})
if err != nil {
        panic(err)
}

Update MaxMessageSize/read limit for realtime message subscription

• The default MaxMessageSize is automatically configured by Ably when connection is established with Ably.
• This value defaults to 16kb for free and 64kb for PAYG account, please get in touch if you would like to request a higher limit for your account.
• Upgrading your account to higher limit will automatically update MaxMessageSize property and should accordingly set the client side connection read limit.
• If you are still facing issues when receiving large messages or intentionally want to reduce the limit, you can explicitly update the connection read limit:

client, err = ably.NewRealtime(ably.WithKey("xxx:xxx"))
if err != nil {
        panic(err)
}
client.Connection.SetReadLimit(131072) // Set read limit to 128kb, overriding default ConnectionDetails.MaxMessageSize

Note - If connection read limit is less than size of received message, the client will throw an error "failed to read: read limited at {READ_LIMIT + 1} bytes" and will close the connection.

Using the REST API

Introduction

All examples assume a client and/or channel has been created as follows:

client, err := ably.NewREST(ably.WithKey("xxx:xxx"))
if err != nil {
        panic(err)
}
channel := client.Channels.Get("test")

Publishing a message to a channel

err = channel.Publish(ctx, "HelloEvent", "Hello!")
if err != nil {
        panic(err)
}
// You can also publish multiple messages in a single request.
err = channel.PublishMultiple(ctx, []*ably.Message{
        {Name: "HelloEvent", Data: "Hello!"},
        {Name: "ByeEvent", Data: "Bye!"},
})
if err != nil {
        panic(err)
}
// A REST client can publish messages on behalf of another client
// by providing the connection key of that client.
err := channel.Publish(ctx, "temperature", "12.7", ably.PublishWithConnectionKey("connectionKeyOfAnotherClient"))
if err != nil {
        panic(err)
}

Querying the History

pages, err := channel.History().Pages(ctx)
if err != nil {
        panic(err)
}
for pages.Next(ctx) {
        for _, message := range pages.Items() {
                fmt.Println(message)
        }
}
if err := pages.Err(); err != nil {
        panic(err)
}

Presence on a channel

pages, err := channel.Presence.Get().Pages(ctx)
if err != nil {
        panic(err)
}
for pages.Next(ctx) {
        for _, presence := range pages.Items() {
                fmt.Println(presence)
        }
}
if err := pages.Err(); err != nil {
        panic(err)
}

Querying the Presence History

pages, err := channel.Presence.History().Pages(ctx)
if err != nil {
        panic(err)
}
for pages.Next(ctx) {
        for _, presence := range pages.Items() {
                fmt.Println(presence)
        }
}
if err := pages.Err(); err != nil {
        panic(err)
}

Fetching your application's stats

pages, err := client.Stats().Pages(ctx)
if err != nil {
        panic(err)
}
for pages.Next(ctx) {
        for _, stat := range pages.Items() {
                fmt.Println(stat)
        }
}
if err := pages.Err(); err != nil {
        panic(err)
}

Getting the channel status

status, err := channel.Status(ctx)
if err != nil {
        panic(err)
}
fmt.Print(status, status.ChannelId)

Configure logging

• By default, internal logger prints output to stdout with default logging level of warning.
• You need to create a custom Logger that implements ably.Logger interface.
• There is also an option provided to configure loglevel.

type customLogger struct {
	*log.Logger
}

func (s *customLogger) Printf(level ably.LogLevel, format string, v ...interface{}) {
	s.Logger.Printf(fmt.Sprintf("[%s] %s", level, format), v...)
}

func NewCustomLogger() *customLogger {
	logger := &customLogger{}
	logger.Logger = log.New(os.Stdout, "", log.LstdFlags)
	return logger
}

client, err = ably.NewRealtime(
        ably.WithKey("xxx:xxx"),
        ably.WithLogHandler(NewCustomLogger()),
        ably.WithLogLevel(ably.LogWarning),
)

Note on usage of ablytest package

Although the ablytest package is available as a part of ably-go, we do not recommend using it as a sandbox for your own testing, since it's specifically intended for client library SDKs and we don’t provide any guarantees for support or that it will remain publicly accessible. It can lead to unexpected behaviour, since some beta features may be deployed on the sandbox environment so that they can be tested before going into production.

You should rather use, ably.NewRealtime by passing the ABLY_KEY, which would be using the Ably production environment.

client, err := ably.NewRealtime(ably.WithKey("xxx:xxx"))

You can also use the control api to setup a test environment using https://github.com/ably/ably-control-go/.

Resources

Demo repositories hosted at ably-labs which use ably-go.

• Ableye
• AblyD
• Ably Go Terminal Chat
• Broadcasting messages in Go with Ably and Redis
• Sync Edit
• Word Game

Broaden your knowledge of realtime in Go with these useful materials:

• Building realtime apps with Go and WebSockets: client-side considerations
• Guide to Pub/Sub in Golang

Requirements

Supported Versions of Go

Whenever a new version of Go is released, Ably adds support for that version. The Go Release Policy supports the last two major versions. This SDK follows the same policy of supporting the last two major versions of Go.

Breaking API Changes in Version 1.2.x

Please see our Upgrade / Migration Guide for notes on changes you need to make to your code to update it to use the new API introduced by version 1.2.x.

Users updating from version 1.1.5 of this library will note that there are significant breaking changes to the API. Our current approach to versioning is not compliant with semantic versioning, which is why these changes are breaking despite presenting only a change in the minor component of the version number.

Feature support

This library targets the Ably 1.2 client library specification. List of available features for our client library SDKs can be found on our feature support matrix page.

Known limitations

As of release 1.2.0, the following are not implemented and will be covered in future 1.2.x releases. If there are features that are currently missing that are a high priority for your use-case then please contact Ably customer support. Pull Requests are also welcomed.

REST API

• Push notifications admin API is not implemented.

• JWT authentication is not implemented.

Realtime API

• There is no channel suspended state; this means that the client will not automatically reattach to channels if a connection becomes suspended and then resumes, and presence members associated with the client will not be automatically re-entered.

• Inband reauthentication is not supported; expiring tokens will trigger a disconnection and resume of a realtime connection.

• Realtime connection failure handling is partially implemented.

• Realtime Ping function is not implemented.

• Message Delta Compression is not implemented.

• Push Notification Target functional is not applicable for the SDK and thus not implemented.

Support, feedback and troubleshooting

Please visit https://faqs.ably.com/ for access to our knowledgebase. If you require support, please visit https://ably.com/support to submit a support ticket.

You can also view the community reported Github issues.

Contributing

For guidance on how to contribute to this project, see CONTRIBUTING.md.