Add iOS 18+ Broadcast Push Notifications Support

[kylebrowning]

Implements support for Apple's broadcast push notification channels introduced in iOS 18, addressing #205.

Overview

This PR adds complete broadcast channel management functionality to APNSwift, allowing developers to create, read, update, and delete broadcast channels through Apple's broadcast API.

What's New

Core Implementation (APNSCore)

• New types for broadcast channels:
  • APNSBroadcastEnvironment - Production/sandbox broadcast endpoints
  • APNSBroadcastChannel - Channel configuration model
  • APNSBroadcastChannelList - List of channel IDs
  • APNSBroadcastRequest - Generic request type with operation routing
  • APNSBroadcastResponse - Generic response type
  • APNSBroadcastMessageStoragePolicy - Enum for storage options
  • APNSBroadcastClientProtocol - Protocol with convenience methods

Client Implementation (APNS)

• APNSBroadcastClient - Full-featured client supporting:
  • POST /channels - Create new broadcast channels
  • GET /channels - List all channels
  • GET /channels/{id} - Read channel details
  • DELETE /channels/{id} - Delete channels
  • Proper HTTP method routing and error handling

Test Infrastructure (APNSTestServer)

• APNSBroadcastTestServer - Real SwiftNIO HTTP server that mocks Apple's broadcast API
  • In-memory channel storage
  • Full CRUD operation support
  • Proper error responses (404, 400)
  • Request ID generation

Tests

• 13 new tests covering:
  • Unit tests for encoding/decoding broadcast types
  • Integration tests with mock server
  • Error handling and edge cases
• All 38 tests pass (existing + new)

Usage Example

let client = APNSBroadcastClient(
authenticationMethod: .jwt(
privateKey: privateKey,
keyIdentifier: "KEY_ID",
teamIdentifier: "TEAM_ID"
),
environment: .production,
eventLoopGroupProvider: .createNew,
responseDecoder: JSONDecoder(),
requestEncoder: JSONEncoder()
)

// Create a broadcast channel
let channel = APNSBroadcastChannel(messageStoragePolicy: .mostRecentMessageStored)
let response = try await client.create(channel: channel)
let channelID = response.body.channelID!

// List all channels
let allChannels = try await client.readAllChannelIDs()

// Delete a channel
try await client.delete(channelID: channelID)

Implementation Details

• Preserves API compatibility: Internal access control maintained to avoid breaking changes
• Protocol-based design: Easy to mock and test in consumer code
• Type-safe operations: Generic request/response types with proper Swift concurrency support
• Comprehensive testing: Includes both unit and integration tests with a real NIO-based mock server

Changes from Original Branch

This PR builds on the work started in https://github.com/eliperkins/APNSwift/tree/channels but completes the implementation:

• ✅ Fixed incomplete send() method
• ✅ Added proper HTTP method routing (GET/POST/DELETE)
• ✅ Correct endpoint construction for all operations
• ✅ Added comprehensive tests
• ✅ Created mock server for testing
• ✅ Full documentation

Testing

Run all tests

swift test

Run only broadcast tests

swift test --filter Broadcast

Documentation

See BROADCAST_CHANNELS.md for:

• Complete usage examples
• Architecture decisions
• Testing guide with mock server
• Future enhancement ideas

Related

Closes #205