Hosts and Clients

Roles

Crosslink has two roles:

Role	Runs on	SDK	Purpose
Host	Desktop/server (Node.js)	`@crosslink/sdk-node`	Exposes RPC methods, manages sessions
Client	Browser/phone	`@crosslink/sdk-browser`	Calls RPC methods, receives events

Host

The host is the application that:

Declares capabilities
Generates pairing codes
Exposes RPC methods
Manages client sessions
Stores the identity key (in OS keychain)

Creating a host

import { createCrosslinkServer } from "@crosslink/sdk-node";

const host = createCrosslinkServer({
  application: { id: "com.example.myapp", name: "My App", version: "1.0.0" },
  capabilities: [
    { id: "app.control", title: "Control the app", risk: "medium" }
  ],
  signalingUrl: "http://127.0.0.1:8081",
  relayUrl: "http://127.0.0.1:8082",
  lan: { bind: "loopback" }
});

Host methods

Method	Description
`host.start()`	Start listening for connections
`host.stop()`	Gracefully shut down
`host.getPairingCode()`	Generate a new pairing code
`host.expose(method, handler, options)`	Register an RPC method
`host.declareEvent(name)`	Declare an event that can be emitted
`host.emit(name, payload)`	Send an event to all connected clients
`host.listDevices()`	List all paired devices
`host.revokeDevice(deviceId)`	Revoke a client’s access

Client

The client is the interface that:

Scans QR codes to pair
Calls RPC methods
Subscribes to events
Manages paired-app records

Creating a client

import { CrosslinkClient } from "@crosslink/sdk-browser";

// Recommended: encrypted storage
const client = await CrosslinkClient.create({
  deviceName: "My Phone",
  onConfirmPairing: async ({ sas, grantedCaps }) => {
    console.log(`SAS: ${sas}`);
    return true;
  }
});

Client methods

Method	Description
`client.pairFromQr(uri, requestedCaps)`	Pair with a host via QR/URI
`client.connect(requestedCaps)`	Connect to a paired host
`client.disconnect()`	Disconnect from the host
`client.forget(appId)`	Remove a paired host
`client.listApps()`	List all paired hosts

Client storage

Use CrosslinkClient.create() instead of new CrosslinkClient(). The factory encrypts the identity seed at rest; the constructor stores it in plaintext.

Storage	Encrypted	Persistent	Best for
`IndexedDbSecureStorage`	Yes (AES-256-GCM)	Yes	Production browsers
`LocalStorageSecureStorage`	No	Yes	Fallback
`MemorySecureStorage`	No	No	Tests

Host storage

The host stores its identity key and paired-device records:

Backend	Encrypted	Requires
keytar	Yes (OS keychain)	The host app installing the optional `keytar` npm package (not a Crosslink dependency)
Electron safeStorage	Yes (OS vault)	Electron runtime
Encrypted file	Yes (AES-256-GCM)	`CROSSLINK_SECRET_KEY` or machine-bound key
Plaintext file	No	Explicit opt-in

Multiple clients

A host can serve multiple clients simultaneously:

Host
├── Client A (phone) -- app.control, app.read
├── Client B (tablet) -- app.read only
└── Client C (laptop) -- app.control, app.read, app.write

Each client has its own session, capabilities, and encryption keys.

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CONCEPTS

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SECURITY

GUIDES

REFERENCE

RESOURCES

Roles

Host

Creating a host

Host methods

Client

Creating a client

Client methods

Client storage

Host storage

Multiple clients

​Roles

​Host

​Creating a host

​Host methods

​Client

​Creating a client

​Client methods

​Client storage

​Host storage

​Multiple clients

Roles

Host

Creating a host

Host methods

Client

Creating a client

Client methods

Client storage

Host storage

Multiple clients