Custom Adapters

Build a channel adapter from the ChannelPort interface to a working platform integration

Channel adapters connect Comis to chat platforms. Each adapter implements the ChannelPort interface from @comis/core, which defines messaging operations (send, receive, edit, delete, react). This guide walks you through building a complete adapter, using the EchoChannelAdapter as a reference implementation.

ChannelPort Interface

The ChannelPort interface defines the contract that every channel adapter must implement. It covers the full messaging lifecycle: connecting, receiving messages, sending responses, and disconnecting.

import type { Result } from "@comis/shared";
import type {
  NormalizedMessage,
  SendMessageOptions,
  AttachmentPayload,
  FetchMessagesOptions,
  FetchedMessage,
} from "@comis/core";
import type { ChannelStatus } from "@comis/core";

export interface ChannelPort {
  /** Unique identifier for this adapter instance (e.g., "telegram-bot-123") */
  readonly channelId: string;
  /** Channel type this adapter handles (e.g., "telegram", "discord") */
  readonly channelType: string;

  // Lifecycle
  start(): Promise<Result<void, Error>>;
  stop(): Promise<Result<void, Error>>;

  // Messaging
  sendMessage(channelId: string, text: string, options?: SendMessageOptions): Promise<Result<string, Error>>;
  editMessage(channelId: string, messageId: string, text: string): Promise<Result<void, Error>>;
  reactToMessage(channelId: string, messageId: string, emoji: string): Promise<Result<void, Error>>;
  removeReaction(channelId: string, messageId: string, emoji: string): Promise<Result<void, Error>>;
  deleteMessage(channelId: string, messageId: string): Promise<Result<void, Error>>;
  fetchMessages(channelId: string, options?: FetchMessagesOptions): Promise<Result<FetchedMessage[], Error>>;
  sendAttachment(channelId: string, attachment: AttachmentPayload, options?: SendMessageOptions): Promise<Result<string, Error>>;

  // Handler
  onMessage(handler: (msg: NormalizedMessage) => void): void;

  // Extension
  platformAction(action: string, params: Record<string, unknown>): Promise<Result<unknown, Error>>;
  getStatus?(): ChannelStatus;
}

You do not need to implement every method fully. Methods like editMessage, reactToMessage, fetchMessages, and platformAction can return err(new Error("Not supported")) if your platform does not support them. The system uses ChannelCapability metadata to know which features are available.

File Structure

The canonical file structure for a channel adapter follows this layout:

packages/channels/src/<platform>/
  <platform>-adapter.ts            # Implements ChannelPort
  message-mapper.ts                # Normalizes platform messages to NormalizedMessage
  media-handler.ts                 # Platform-specific attachment handling
  credential-validator.ts          # Validates platform API credentials
  <platform>-resolver.ts           # Implements MediaResolverPort (optional)
  voice-sender.ts                  # Platform-specific voice sending (optional)
  <platform>-plugin.ts             # Implements ChannelPluginPort

Not every file is required. At minimum you need the adapter (implements ChannelPort) and the plugin wrapper (implements ChannelPluginPort).

Tutorial: Building a Minimal Adapter

1. Implement ChannelPort

   Create the adapter class that implements the ChannelPort interface. The EchoChannelAdapter at packages/channels/src/echo/echo-adapter.ts (251 lines) is the simplest real example to reference.

   // packages/channels/src/myplatform/myplatform-adapter.ts
   import { ok, err, type Result } from "@comis/shared";
   import type {
     ChannelPort,
     MessageHandler,
     NormalizedMessage,
     SendMessageOptions,
     AttachmentPayload,
     FetchMessagesOptions,
     FetchedMessage,
   } from "@comis/core";
   
   export class MyPlatformAdapter implements ChannelPort {
     readonly channelId: string;
     readonly channelType = "myplatform";
     private messageHandler?: MessageHandler;
   
     constructor(config: { channelId: string; apiKey: string }) {
       this.channelId = config.channelId;
     }
   
     async start(): Promise<Result<void, Error>> {
       // Connect to your platform's API or WebSocket
       return ok(undefined);
     }
   
     async stop(): Promise<Result<void, Error>> {
       // Disconnect and clean up resources
       return ok(undefined);
     }
   
     async sendMessage(
       channelId: string,
       text: string,
       options?: SendMessageOptions,
     ): Promise<Result<string, Error>> {
       // Send via your platform's API, return the message ID
       try {
         const messageId = await this.platformSend(channelId, text);
         return ok(messageId);
       } catch (e) {
         return err(e instanceof Error ? e : new Error(String(e)));
       }
     }
   
     async editMessage(
       channelId: string,
       messageId: string,
       text: string,
     ): Promise<Result<void, Error>> {
       return err(new Error("Not supported"));
     }
   
     async reactToMessage(
       channelId: string,
       messageId: string,
       emoji: string,
     ): Promise<Result<void, Error>> {
       return err(new Error("Not supported"));
     }
   
     async removeReaction(
       channelId: string,
       messageId: string,
       emoji: string,
     ): Promise<Result<void, Error>> {
       return err(new Error("Not supported"));
     }
   
     async deleteMessage(
       channelId: string,
       messageId: string,
     ): Promise<Result<void, Error>> {
       return err(new Error("Not supported"));
     }
   
     async fetchMessages(
       channelId: string,
       options?: FetchMessagesOptions,
     ): Promise<Result<FetchedMessage[], Error>> {
       return err(new Error("Not supported"));
     }
   
     async sendAttachment(
       channelId: string,
       attachment: AttachmentPayload,
       options?: SendMessageOptions,
     ): Promise<Result<string, Error>> {
       return err(new Error("Not supported"));
     }
   
     async platformAction(
       action: string,
       params: Record<string, unknown>,
     ): Promise<Result<unknown, Error>> {
       return err(new Error(`Unsupported action: ${action} on myplatform`));
     }
   
     onMessage(handler: MessageHandler): void {
       this.messageHandler = handler;
     }
   
     // Call this when your platform receives a message
     private handleIncomingMessage(platformMsg: unknown): void {
       if (!this.messageHandler) return;
   
       const normalized: NormalizedMessage = this.normalizeMessage(platformMsg);
       this.messageHandler(normalized);
     }
   }
   
2. Normalize incoming messages

   When your platform receives a message, convert it to a NormalizedMessage before passing it to the handler. This is the standard message format that all of Comis understands.

   Key fields of NormalizedMessage:

   Field	Type	Description
   id	string	Platform message ID
   text	string	Message text content
   channelId	string	Channel or chat ID
   senderId	string	User who sent the message
   senderName	string	Display name of the sender
   timestamp	number	When the message was sent (epoch ms)
   attachments	MessageAttachment[]	Array of file/media attachments
   isGroup	boolean	Whether this is a group chat
   replyTo	object	Message being replied to (optional)

   Create a message-mapper.ts file to keep the normalization logic separate from the adapter:

   // packages/channels/src/myplatform/message-mapper.ts
   import type { NormalizedMessage } from "@comis/core";
   
   export function mapToNormalized(platformMsg: PlatformMessage): NormalizedMessage {
     return {
       id: platformMsg.messageId,
       text: platformMsg.body ?? "",
       channelId: platformMsg.chatId,
       senderId: platformMsg.authorId,
       senderName: platformMsg.authorName ?? "Unknown",
       timestamp: platformMsg.createdAt,
       attachments: [],
       isGroup: platformMsg.isGroupChat,
     };
   }
   
3. Define ChannelCapability metadata

   The ChannelCapability schema describes what your adapter supports. The system uses this metadata for feature negotiation — for example, deciding whether to attempt streaming or threading on your channel.

   import type { ChannelCapability } from "@comis/core";
   
   const capabilities: ChannelCapability = {
     chatTypes: ["dm", "group"],
     features: {
       reactions: true,
       editMessages: false,
       deleteMessages: false,
       fetchHistory: false,
       attachments: true,
       threads: false,
       mentions: true,
       formatting: ["markdown"],
       buttons: false,
       cards: false,
       effects: false,
     },
     limits: {
       maxMessageChars: 4096,
     },
     streaming: {
       supported: true,
       throttleMs: 300,
       method: "edit",
     },
     threading: {
       supported: false,
       threadType: "none",
     },
   };
   

   Set each feature flag honestly. The system trusts your declared capabilities to decide how to deliver messages. For example, if streaming.supported is false, Comis will send complete messages instead of streaming edits.

4. Create the ChannelPluginPort wrapper

   Wrap your adapter in a ChannelPluginPort for registration with the plugin system. The plugin provides metadata (ID, name, capabilities) and lifecycle hooks (activate, deactivate).

   Reference packages/channels/src/echo/echo-plugin.ts for the simplest real example:

   // packages/channels/src/myplatform/myplatform-plugin.ts
   import { ok, type Result } from "@comis/shared";
   import type { ChannelCapability, ChannelPluginPort, PluginRegistryApi } from "@comis/core";
   import { MyPlatformAdapter } from "./myplatform-adapter.js";
   
   export interface MyPlatformConfig {
     channelId: string;
     apiKey: string;
   }
   
   export function createMyPlatformPlugin(config: MyPlatformConfig): ChannelPluginPort {
     const adapter = new MyPlatformAdapter(config);
   
     return {
       id: "channel-myplatform",
       name: "MyPlatform Channel",
       version: "1.0.3",
       channelType: "myplatform",
       capabilities,
       adapter,
   
       register(registry: PluginRegistryApi): Result<void, Error> {
         // Register hooks if needed (e.g., before_send, after_tool_call)
         return ok(undefined);
       },
   
       async activate(): Promise<Result<void, Error>> {
         return adapter.start();
       },
   
       async deactivate(): Promise<Result<void, Error>> {
         return adapter.stop();
       },
     };
   }
   
5. Register and test

   The plugin is registered through the PluginRegistry during bootstrap. The channel registry validates your declared capabilities against the ChannelCapabilitySchema at registration time.

   For testing, use the co-located test pattern. Create myplatform-adapter.test.ts alongside the adapter and test:

   • Lifecycle: start() returns ok, stop() returns ok
   • Message sending: sendMessage() returns a message ID
   • Message receiving: Call onMessage() handler with a normalized message and verify it processes correctly
   • Unsupported operations: Methods that return err() do so with descriptive messages

   // packages/channels/src/myplatform/myplatform-adapter.test.ts
   import { describe, it, expect } from "vitest";
   import { MyPlatformAdapter } from "./myplatform-adapter.js";
   
   describe("MyPlatformAdapter", () => {
     it("starts and stops cleanly", async () => {
       const adapter = new MyPlatformAdapter({ channelId: "test", apiKey: "key" });
       const startResult = await adapter.start();
       expect(startResult.ok).toBe(true);
   
       const stopResult = await adapter.stop();
       expect(stopResult.ok).toBe(true);
     });
   });
   

Reference: EchoChannelAdapter

The EchoChannelAdapter is the canonical reference implementation. It is an in-memory adapter with no external dependencies, used extensively in integration tests. Located at packages/channels/src/echo/echo-adapter.ts (251 lines).

The Echo adapter implements every ChannelPort method by storing data in memory maps. It also provides test helper methods like injectMessage() (simulates incoming messages) and getSentMessages() (retrieves sent messages for assertions).

Study this adapter to see every ChannelPort method implemented correctly with the Result pattern.

Reference: Real Adapters

For more complex adapter implementations, reference these production adapters:

• Telegram — The most complete adapter with 8 files. Webhook and polling modes, rich reactions, voice messages, platform actions (pin, kick, poll, ban). Located at packages/channels/src/telegram/.
• Discord — Rich feature support including buttons, embeds, reactions, threads, and guild management. Located at packages/channels/src/discord/.
• Slack — Block Kit integration with both Socket Mode and HTTP mode. Located at packages/channels/src/slack/.

Each production adapter follows the same file structure pattern, with additional files for media handling, credential validation, and platform-specific message mapping.

Related

Architecture

Port interfaces and hexagonal pattern

Plugins

General plugin system (hooks, tools, routes)

Event Bus

Channel events your adapter should emit

Channels Overview

User-facing channel documentation