Channels and Messages

In a Programmable Chat application, a Channel is where all the action happens. Whether a chat is between two users or two hundred, a Channel is where messages are sent, received, and archived for later viewing by offline clients.

Programmable Chat has two objects for working with channels - Channel Descriptors and Channels. A Channel Descriptor is a lightweight representation of the key attributes of a public or private channel. When requesting a list of channels, you will receive Channel Descriptors that serve as a snapshot in time for each channel. These channel attributes will not update if modified remotely, so you should use the descriptors only to assist your user in discovering and joining a channel.

Channel Descriptors can be used to obtain a full channel object or view the following information:

• Channel SID
• Friendly Name
• Unique Name
• Date Created
• Created By
• Date Updated
• Channel Attributes
• Messages and Members Count
• Last Consumed Message Index (if available)
• Status (if available)
• Type (private or public)

A full Channel object allows you to join and interact with the channel. Let's dive into a few of the key techniques you'll need to employ while working with channels and messages in your application.

• Listing public channel descriptors
• Listing user channel descriptors
• Get a channel from a channel descriptor
• Create a channel
• Join a channel
• Send messages to a channel
• Get most recent messages from a channel
• Invite other users to a channel
• Accept an invitation to a channel
• Get a list of subscribed channels
• Subscribe for channel events
• Delete a channel

List Public Channel Descriptors

If your programmable chat instance has public channels that are discoverable by a user, you can fetch a list of Channel Descriptors for all public channels in the system:

List User Channel Descriptors

If your programmable chat instance has user channels that the current user belongs to, you can fetch a list of User Channel Descriptors for this user. To list public channels that have not yet been joined, see list public channels above.

Get A Channel from a Channel Descriptor

After you have retrieved a list of channel descriptors, you will typically want to get a specific Channel and interact with it directly. In the following example, you can see how. Note that this is not necessary for the Javascript Chat SDK as the client.getChannel() gets the channel descriptor and instantiates the channel internally for you.

Create a Channel

Before you can start sending messages, you first need a Channel that can receive messages. Here is how you create a channel.

Join a Channel

Once you've created a channel, a user must join it to begin receiving or sending messages on that channel.

Send Messages to a Channel

Once you're a member of a channel, you can send a message to it.

A message is a bit of data that is sent first to the Twilio backend where it is stored for later access by members of the channel. The message is then pushed out in real time to all channel members currently online. Only users subscribed to your channel will receive your messages.

Today, a message is just a string of text. Available in beta you can also send other media types, like images and binary data.

Get the Most Recent Messages from a Channel

With a channel object in hand, you can fetch the most recent messages from the channel. Use this to provide history within the channel. You can choose how many messages you want to retrieve.

You can also be notified of any new incoming messages with an event handler. Use this handler to update your user interface to display new messages.

Invite other Users to a Channel

Sometimes you might feel lonely in a channel. Rather than sending messages to yourself, invite a friend to come and chat! It doesn't matter if the channel is public or private - you are always able to invite another user to any channel you own.

Accept an Invitation to a Channel

Social acceptance is a great feeling. Accepting an invite to a channel means you too can partake in banter with other channel members.

Get a List of Subscribed Channels

Listing subscribed channels lets you perform actions on them as a channel member (e.g., invite or display). This method only shows the channels where the current programmable chat user is a member. To list public channels that have not yet been joined, see list public channels above.

Subscribe for Channel Events

Channels are a flurry of activity. Members join and leave, messages are sent and received, and channel states change. As a member of a channel, you'll want to know the status of the channel. You may want to receive a notification when the channel is deleted or changed. Channel event listeners help you do just that.

These event listeners will notify your app when a channel's state changes. Once you receive the notification, you can perform the necessary actions in your app to react to it.

Your event listeners will also notify your app when channel members perform some action (including when they leave, join, change, or start/stop typing). Using these listeners, you can provide real-time updates to your application users.

Delete a Channel

Deleting a channel both deletes the message history and removes all members from it.

You can only delete channels that you have permissions to delete. Deleting a channel means it cannot be retrieved at a later date for any reason. Delete with caution!

Now that you know all there is to know about channels, might we suggest learning more about the REST API? With the REST API, you can execute many of these same actions from your server-side code.

Next: Media Support in Chat