pubnub/pubnub-app-developer

Build real-time applications with PubNub pub/sub messaging

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PubNub Channels Guide

Name: pubnub/pubnub-app-developer
Author: pubnub

What is a Channel?

Channels are named pathways for routing messages in PubNub. They act as labels that connect publishers with subscribers.

Key Characteristics

Dynamic Creation: Channels exist when used - no pre-registration needed
Lightweight: No additional cost for number of channels used
Unlimited: Use as many channels as your application requires
Case-Sensitive: MyChannel and mychannel are different

Channel Naming Rules

Valid Names

Length: Up to 92 characters
Character Set: UTF-8 compatible

Invalid Characters (DO NOT USE)

Character	Name
`,`	Comma
`:`	Colon
`*`	Asterisk
`/`	Slash
`\`	Backslash
	Space
`.`	Period (reserved for wildcards)

Naming Conventions

// Good channel names
'chat-room-123'
'user_notifications_alice'
'sports-scores-nba'
'iot-sensor-device42'

// Bad channel names (will cause errors)
'chat room'      // space
'user:alice'     // colon
'sports/nba'     // slash
'alerts.*'       // wildcard (use only for subscriptions)

Channel Design Patterns

1. Direct Messaging (1:1 Chat)

// Convention: Sort user IDs alphabetically for consistent channel name
function getDirectChannelName(userId1, userId2) {
  const sorted = [userId1, userId2].sort();
  return `dm-${sorted[0]}-${sorted[1]}`;
}

// Results in: 'dm-alice-bob' (always the same regardless of who initiates)

2. Group Chat Rooms

// Room-based channels
'room-project-alpha'
'room-social-lounge'
'room-support-team'

// With namespace prefix
'chat-group-12345'

3. User-Specific Channels

// Personal notifications
`user-notifications-${userId}`

// User activity feed
`user-feed-${userId}`

// User presence channel
`user-status-${userId}`

4. Hierarchical Topics (for Wildcard Subscribe)

// Sports hierarchy
'sports.football.scores'
'sports.basketball.news'
'sports.baseball.highlights'

// IoT sensor hierarchy
'iot.building1.floor2.temp'
'iot.building1.floor2.humidity'

// Subscribe to all with wildcard
pubnub.subscribe({ channels: ['sports.*'] });

5. Device/IoT Channels

// Device telemetry
`device-telemetry-${deviceId}`

// Device commands
`device-commands-${deviceId}`

// Fleet-wide broadcasts
'devices-all-updates'

Wildcard Subscriptions

Requires: Stream Controller enabled in Admin Portal

Pattern Rules

Wildcard (*) must be at the end of the pattern
Maximum two dots (three levels)
Period (.) is the hierarchy delimiter

Valid Patterns

// One level
pubnub.subscribe({ channels: ['news.*'] });
// Matches: news.sports, news.weather, news.politics

// Two levels
pubnub.subscribe({ channels: ['iot.building1.*'] });
// Matches: iot.building1.temp, iot.building1.humidity

Invalid Patterns

// Wildcard not at end - INVALID
'news.*.sports'

// Too many levels - INVALID
'a.b.c.d.*'

// Wildcard at start - INVALID
'*.notifications'

Channel Groups

Requires: Stream Controller enabled in Admin Portal

Channel Groups allow subscribing to thousands of channels efficiently.

Limits

Resource	Limit
Channels per group	2,000
Groups per client	10
Total channels via groups	20,000

Creating and Managing Groups

// Add channels to a group
await pubnub.channelGroups.addChannels({
  channelGroup: 'user-alice-feeds',
  channels: ['feed-news', 'feed-sports', 'feed-tech']
});

// Subscribe to the group
pubnub.subscribe({
  channelGroups: ['user-alice-feeds']
});

// Remove channels from group
await pubnub.channelGroups.removeChannels({
  channelGroup: 'user-alice-feeds',
  channels: ['feed-tech']
});

// List channels in group
const result = await pubnub.channelGroups.listChannels({
  channelGroup: 'user-alice-feeds'
});
console.log('Channels:', result.channels);

// Delete entire group
await pubnub.channelGroups.deleteChannelGroup({
  channelGroup: 'user-alice-feeds'
});

Important Notes

Cannot publish to group: Always publish to individual channels
Cannot use wildcards in groups: Wildcard patterns not allowed
Group must have channels: Subscribe to empty group returns 400 error

Multiplexing

Subscribe to multiple named channels over a single connection.

// Subscribe to up to 30 channels (recommended max)
pubnub.subscribe({
  channels: ['chat-room', 'notifications', 'presence-updates']
});

When to Use What

Scenario	Approach
< 30 channels	Multiplexing
30-2,000 channels	Channel Groups
> 2,000 channels	Multiple Channel Groups
Hierarchical data	Wildcard Subscribe

Channel Access Control

By default, any client can publish/subscribe to any channel. Use Access Manager to restrict:

// Server-side: Grant read access to specific channel
await pubnub.grant({
  channels: ['private-room-123'],
  authKeys: ['user-auth-token'],
  read: true,
  write: false,
  ttl: 60  // minutes
});

Message Buffer (Short-Term Cache)

Each channel maintains a short-term buffer:

Holds last 100 messages
Retention: up to ~20 minutes
Used for quick catch-up after brief disconnects
High publish rates push old messages out faster

For longer storage, enable Message Persistence add-on.

Best Practices

Use descriptive, hierarchical names when planning for wildcards
Avoid special characters - stick to alphanumeric, hyphens, underscores
Keep names short but meaningful (92 char limit)
Document your channel naming scheme for team consistency
Use Channel Groups for user-specific aggregations (feeds, notifications)
Plan for scale - structure channels for wildcard patterns if needed

Install with Tessl CLI

npx tessl i pubnub/pubnub-app-developer

evals

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