mtp/docs/WASM-CLIENT.md

MTP WASM Client

The browser client is exposed through the mtp npm package. Most applications should use the SDK-first MTPClient API; direct generated WASM bindings remain available from mtp/raw for advanced integrations.

Browser Compatibility

The SDK requires the browser to expose WebTransport. MTPClient.isSupported() is the runtime check. A browser without WebTransport cannot connect through this client.

Requirement	Check
WebTransport API	MTPClient.isSupported()
Certificate trust	Browser validation or serverCertificateHashes
Secure context	Serve the application from HTTPS where required by the browser
Generated bindings	Run the Vite integration during development and build

Package Entry Points

import { MTPClient } from "mtp";
import init, { WasmClient } from "mtp/raw";
import { mtp } from "mtp/vite";

• mtp exports the SDK-first MTPClient wrapper.
• mtp/raw exports the generated wasm-bindgen module and raw classes/functions.
• mtp/vite exports the Vite plugin that builds app-specific WASM bindings from your type-maps.yaml.
• mtp/type-map exports generated TypeScript unions for communication and data type names.

Vite Type-Map Workflow

Browser apps provide their own type map. The Vite plugin runs wasm-pack during dev and build with MTP_TYPE_MAPS set, writes generated output under node_modules/.vite/mtp/ by default, and aliases mtp/raw plus mtp/type-map to that generated output. Configuration: Type Map.

You do not need to publish, fork, or copy an app-specific generated WASM package.

The web client example shows the entry point. Its Vite configuration shows the generated binding integration.

SDK Quick Start

import { MTPClient } from "mtp";

const client = await MTPClient.create({
  url: "https://host.example.com:4433",
  hostPublicKey,
  credentials,
  storage,
  serverCertificateHashes: ["sha-256:abcd1234..."],
  maxMessageSize: 1_000_000,
  authTimeoutMs: 30_000,
  pings: true,
  logger: (event) => console.log(event),
});

const unsubscribe = client.subscribe("SomeType", (message) => {
  console.log(message.type, message.data);
});

if (client.credentials?.clientId == null) {
  await client.register();
} else {
  await client.connect();
}
await client.send("SomeType", { value: "hello" });

const response = await client.request(
  "SomeRequestType",
  { id: "abc" },
  { responseType: "SomeResponseType" },
);

client.raw.client;   // underlying WasmClient instance
client.raw.bindings; // generated raw WASM module exports

unsubscribe();
client.disconnect();

MTPClient.isSupported() checks whether the current browser exposes WebTransport:

if (!MTPClient.isSupported()) {
  throw new Error("WebTransport is not available in this browser");
}

MTPClient Options

Option	Default	Purpose
url	Required	WebTransport endpoint.
descriptor	None	Client label sent during connection setup.
hostPublicKey	None	Host public key bundle for authenticated login or registration.
credentials	None	Existing client ID and serialized keyring.
credentialsStorageKey	mtp:credentials	Key used by configured credential storage.
storage	None	Sync or async credential storage adapter.
serverCertificateHashes	Omitted	WebTransport certificate pins.
maxMessageSize	16 MiB	Inbound and outbound frame limit. Values below frame overhead are rejected by the transport.
authTimeoutMs	No SDK timeout	Login and registration timeout. undefined leaves the promise pending until transport or peer failure.
requestTimeoutMs	30 seconds	Default request() timeout.
pings	false	Protocol pings, or an object with intervalMs.
logger	No-op	Receives SDK state and error events.
sessionStorage	In-memory	E2EE session state storage.
encryptedDeviceSecretProvider	In-memory	Device-secret storage for E2EE.

wasm selects a custom generated WASM module. MTPClient.create validates positive safe-integer values for the numeric limits and timeout options.

Differences from Native Client

The browser SDK uses WebTransport and JavaScript promises. The native client uses Rust futures, direct QUIC configuration, and MTPConnection handles. Browser pipes expose promise-based readers and writers; native pipes implement Tokio I/O traits.

Native and Browser Credential Persistence

The storage option supplies the credential adapter. The adapter stores the client ID and serialized keyring after registration and returns them for later connections. The SDK does not select localStorage or IndexedDB for an application. Treat the serialized keyring as private key material.

sessionStorage and encryptedDeviceSecretProvider are separate E2EE session stores. The latter exchanges EncryptedDeviceSecretRecord values through setEncryptedDeviceSecret and getEncryptedDeviceSecret; the application chooses the backing store and protects its wrapping key.

Native and Browser Certificate Checks

WebTransport certificate pins must match the server certificate hash. A pin mismatch is a TLS failure, not an MTP authentication failure. Check the browser network panel, endpoint origin, and WebTransport CONNECT path before inspecting frames.

Credentials And Storage

Authenticated connections need stable key material. Pass credentials when you already have a client ID and serialized keyring, or pass a small storage object and let the SDK persist credentials after registration.

const storage = {
  getItem: (key: string) => localStorage.getItem(key),
  setItem: (key: string, value: string) => localStorage.setItem(key, value),
  removeItem: (key: string) => localStorage.removeItem(key),
};

const client = await MTPClient.create({
  url: "https://host.example.com:4433",
  hostPublicKey,
  storage,
});

const clientId = client.credentials?.clientId == null
  ? await client.register()
  : (await client.connect(), client.credentials.clientId);

The storage contract is intentionally small and may be sync or async:

interface MTPCredentialStorage {
  getItem(key: string): string | null | Promise<string | null>;
  setItem(key: string, value: string): void | Promise<void>;
  removeItem(key: string): void | Promise<void>;
}

credentials can also be supplied directly:

const client = await MTPClient.create({
  url: "https://host.example.com:4433",
  hostPublicKey,
  credentials: {
    clientId: 42n,
    keyring: savedKeyringBytes,
  },
});

await client.connect();

client.credentials returns the current public credential object. Call clearCredentials() to remove in-memory credentials and delete the configured storage key.

Connection Methods

• connect() opens a connection. If credentials include a clientId and hostPublicKey is available, it uses authenticated login; otherwise it uses unauthenticated connect.
• register() performs authenticated registration and persists the assigned client ID when storage is configured.
• disconnect() stops protocol pings and closes the underlying WebTransport session.

For certificate pinning, pass WebTransport certificate hashes:

await MTPClient.create({
  url: "https://host.example.com:4433",
  serverCertificateHashes: ["sha-256:abcd1234..."],
});

If hashes are omitted, the browser uses its normal TLS root store.

maxMessageSize caps inbound and outbound MTP frames before buffering/sending. authTimeoutMs bounds connect/login/register promises at the SDK layer. requestTimeoutMs sets the default timeout for request() calls; a request can override it with timeoutMs in its options.

Streams

The browser client uses one WebTransport session per MTPClient instance. send(), request(), and subscribe() all operate over that session; the SDK does not expose browser stream objects directly.

Use the normal message APIs to send and receive over that session:

const client = await MTPClient.create({ url, hostPublicKey });
await client.connect();

const unsubscribe = client.subscribe("SomeType", (message) => {
  console.log(message.data);
});

await client.send("SomeType", { value: "hello" });
unsubscribe();

Internally, each outbound MTP frame is written to a new WebTransport unidirectional stream as a four-byte big-endian length followed by the frame, then that stream is closed. Incoming frames are read from the session's incoming unidirectional streams. The reader accepts both one-frame streams and native peers that place several frames on a persistent stream, so browser and native clients interoperate without stream configuration.

The SDK owns stream lifetime and framing. Do not create browser streams for MTP frames yourself through the SDK. For direct generated bindings, use client.raw.client or import WasmClient from mtp/raw; a WasmClient still owns one active WebTransport session, so create another instance for an independent connection.

Sending, Requests, Subscriptions, And Pings

send accepts either a typed message or a prebuilt raw frame:

await client.send("SomeType", { value: "hello" });
await client.send(rawFrameBytes);

Typed sends are encoded by the generated WASM binding using the app type map. Optional frame metadata can be passed as the third argument:

await client.send("SomeType", { value: "hello" }, {
  id: 7,
  sender: client.credentials?.clientId ?? 0n,
});

request sends one frame and resolves with the parsed response carrying the same frame id. If the matching response has a different responseType, the promise rejects with a response-type error. A timeout rejects the promise and removes the pending request:

const response = await client.request(
  "SomeRequestType",
  { id: "abc" },
  { responseType: "SomeResponseType" },
);

subscribe registers a message-type handler and returns an unsubscribe function:

const unsubscribe = client.subscribe("SomeType", (message) => {
  console.log(message.id, message.sender, message.data);
});

unsubscribe();

Protocol ping behavior is defined in Protocol Reference. The SDK configuration is:

await MTPClient.create({
  url: "https://host.example.com:4433",
  pings: { intervalMs: 30_000 },
});

Use pings: true for the default interval.

Pipes

Pipes are raw binary streams over QUIC. A pipe starts with a lightweight PipeRequest handshake frame, then the stream carries raw bytes with zero per-frame overhead. Pipes are unidirectional; the peer that initiates the pipe writes, and the peer that accepts it reads.

Outgoing Pipes

createPipe sends a PipeRequest frame and returns a handle. Call wait() to block until the remote peer accepts or denies:

const handle = await client.createPipe("file-transfer");

const writer = await handle.wait();
if (writer == null) {
  console.log("host denied the pipe");
  return;
}

await writer.write(new Uint8Array([0x01, 0x02, 0x03]));
await writer.write(chunk);
await writer.close();

writer.close() sends a QUIC stream FIN. writer.abort() resets the stream abruptly. Each write resolves when the chunk has been handed to the transport; it does not wait for the peer to consume it.

The handle and writer expose pipeId and description:

console.log(handle.pipeId, handle.description);
console.log(writer.pipeId);

Incoming Pipes

Set a handler to receive pipe requests from the remote peer:

client.setOnPipeRequest((request) => {
  console.log("incoming pipe", request.pipeId, request.description);
  // accept or deny asynchronously
});

Accept a request to receive a PipeReader:

client.setOnPipeRequest(async (request) => {
  if (request.description === "file-transfer") {
    const reader = await client.acceptPipe(request.pipeId);

    while (true) {
      const chunk = await reader.read();
      if (chunk == null) break; // stream closed by peer
      processChunk(chunk);
    }
  } else {
    await client.denyPipe(request.pipeId);
  }
});

reader.read() resolves with a Uint8Array or null when the peer closes the stream. The reader exposes pipeId and description:

console.log(reader.pipeId, reader.description);

Pipe Handshake

1. The initiator calls createPipe(description); the SDK sends a PipeRequest frame with a random pipeId and the description.
2. The receiver's setOnPipeRequest callback fires with { pipeId, description }.
3. The receiver calls acceptPipe(pipeId); the SDK sends a PipeResponse with Accepted = true and opens a new unidirectional stream for raw data.
4. The initiator's handle.wait() resolves with a PipeWriter bound to that stream.
5. If the receiver calls denyPipe(pipeId), handle.wait() resolves with null.

Pipes share the same WebTransport session as message frames; they do not need a separate connection.

Logger Events

The SDK logger receives parsed events:

type MTPLogEvent =
  | { hint: "info" | "warning"; type: string; data: unknown }
  | { hint: "error"; type: string | "error"; error: string };

Incoming non-error frames and sent frames are logged as info. Error frames and transport errors are logged as error.

Advanced Raw Bindings

Use mtp/raw when you need direct access to the generated wasm-bindgen API:

import init, {
  ConnectionConfig,
  WasmClient,
  ed25519_generate,
  keyring_from_ed25519,
} from "mtp/raw";

await init();

const rawClient = new WasmClient(
  (state) => console.log("state", state),
  (frame) => console.log("message", frame),
  (error) => console.error(error),
);

const config = new ConnectionConfig("https://host.example.com:4433");
config.client_id = 42n;

await rawClient.connect(config);
config.free();

Raw callbacks receive parsed frames, not application-specific SDK objects:

interface ParsedFrame {
  id?: number;
  type: string;
  sender?: bigint;
  receiver?: bigint;
  data: Record<string, unknown>;
  raw: Uint8Array;
}

Frames

Raw message helpers that remain available include:

• build_frame(messageType, data, options?)
• build_ping_frame(clientId, description, timestamp, data)
• parse_frame(frame)
• format_frame(frame)
• parse_auth_response(frame)

The SDK export also exposes the same frame codec through codec:

import { codec } from "mtp";

const frame = codec.encode("SomeType", { value: "hello" });
const parsed = codec.decode(frame);
const display = codec.format(frame);

Crypto

Raw crypto and key helpers include:

• ed25519_generate()
• ed25519_verify(publicKey, message, signature)
• keyring_generate()
• keyring_from_ed25519(secretKey, publicKey)
• WasmKeyring.from_bytes(bytes) and keyring.to_bytes()
• WasmPublicKeyBundle.from_bytes(bytes) and bundle.to_bytes()
• WasmEd25519Signer
• WasmChaCha20Poly1305
• wasm_sha256, wasm_sha256_double, wasm_hkdf_expand, and wasm_derive_encryption_key

Raw authenticated login and registration map directly to the Rust WASM layer:

const generated = ed25519_generate();
const keyringBytes = keyring_from_ed25519(generated.secretKey, generated.publicKey);

const registeredId = await rawClient.auth_register(
  config,
  hostPublicKeyBytes,
  keyringBytes,
);

const confirmedId = await rawClient.auth_connect(
  config,
  hostPublicKeyBytes,
  keyringBytes,
  registeredId,
);

Pipes

The raw WasmClient exposes the same pipe operations as the SDK wrapper. The shared lifecycle is in Pipes; raw bindings use snake_case names.

rawClient.set_on_pipe_request((event) => {
  void rawClient.accept_pipe(event.pipeId);
});

const handle = await rawClient.create_pipe("file-transfer");
const writer = await handle.wait();
if (writer) {
  await writer.write(chunk);
  await writer.close();
}

A WasmClient manages one active WebTransport session. Create a new instance for independent connections, and call free() or [Symbol.dispose]() on raw WASM objects when you want to release memory eagerly.

State Management

A WasmClient owns one active WebTransport session. Create a separate client for each independent connection. Call free() or [Symbol.dispose]() on raw WASM objects when the application no longer needs them. SDK session and device secret persistence are documented in Security.