# Transport API
URL: /docs/api/transport



Transport API [#transport-api]

Use the transport API when configuring how the runtime client communicates with worker processes. The transport abstracts MessagePort-based RPC over the worker boundary.

Types [#types]

<TypeTable
  type={{
  "name": "RuntimeTransport",
  "description": "Low-level transport interface for kernel command/response messaging.\nPortable across MessagePort, WebSocket, HTTP, and native FFI channels.",
  "entries": [
    {
      "name": "send",
      "description": "Send a command to the runtime worker.",
      "tags": [
        {
          "name": "param",
          "text": "message - The kernel command to send"
        },
        {
          "name": "param",
          "text": "transferables - Optional transferable objects (e.g., MessagePort, ArrayBuffer)"
        }
      ],
      "type": "(message: RuntimeCommand, transferables?: Transferable[]) => void",
      "simplifiedType": "function",
      "required": true,
      "deprecated": false
    },
    {
      "name": "onMessage",
      "description": "Register a handler for incoming kernel responses.",
      "tags": [
        {
          "name": "param",
          "text": "handler - Callback invoked for each response from the worker"
        }
      ],
      "type": "(handler: (message: RuntimeResponse) => void) => void",
      "simplifiedType": "function",
      "required": true,
      "deprecated": false
    },
    {
      "name": "close",
      "description": "Close the transport and release resources.",
      "tags": [],
      "type": "() => void",
      "simplifiedType": "function",
      "required": true,
      "deprecated": false
    }
  ]
}}
/>

createWorkerTransport [#createworkertransport]

`createWorkerTransport(workerUrl)` creates a `RuntimeTransport` that spawns a Web Worker from the given URL and establishes a MessageChannel for bidirectional communication. Returns `RuntimeTransport & { worker: Worker }`.

createInProcessTransport [#createinprocesstransport]

`createInProcessTransport()` creates a `RuntimeTransport` that runs the kernel in the same process using a MessageChannel. No Web Worker is spawned. Use this for testing or Node.js environments where worker isolation is not needed.

Usage [#usage]

Web Worker Transport (Default) [#web-worker-transport-default]

```typescript
import { createRuntimeClient, fromMemoryFS } from '@taucad/runtime';
import { replicad } from '@taucad/runtime/kernels';
import { esbuild } from '@taucad/runtime/bundler';
import { createWorkerTransport } from '@taucad/runtime/transport';

const transport = createWorkerTransport(new URL('@taucad/runtime/worker', import.meta.url).href);

const client = createRuntimeClient({
  kernels: [replicad()],
  bundlers: [esbuild()],
  fileSystem: fromMemoryFS(),
  transport,
});
```

In-Process Transport (Testing) [#in-process-transport-testing]

```typescript
import { createRuntimeClient, fromMemoryFS } from '@taucad/runtime';
import { replicad } from '@taucad/runtime/kernels';
import { esbuild } from '@taucad/runtime/bundler';
import { createInProcessTransport } from '@taucad/runtime/transport';

const client = createRuntimeClient({
  kernels: [replicad()],
  bundlers: [esbuild()],
  fileSystem: fromMemoryFS(),
  transport: createInProcessTransport(),
});
```

When to Use Each [#when-to-use-each]

| Transport                    | Use when                                                  |
| ---------------------------- | --------------------------------------------------------- |
| Default (none specified)     | Standard browser usage. Client auto-creates a worker.     |
| `createWorkerTransport(url)` | Custom worker URL or pre-built worker bundle.             |
| `createInProcessTransport()` | Testing, Node.js, or when worker isolation is not needed. |

Related [#related]

* [Worker Model](../concepts/worker-model)
* [Architecture](../concepts/architecture)
* [Quick Start](../getting-started/quick-start) -- End-to-end setup using the default transport