# @zerolith/client/port

Import from `@zerolith/client/port`. Generated from the source; every signature below is what the published types declare.

## Functions

### portTransport

```ts
function portTransport(port: PortLike): Transport
```

A `Transport` that sends each request over the port as a message and
resolves with the response that comes back under the same id. Aborting
the request's signal rejects the call; the message already sent is
answered and ignored.

Source: `packages/client/src/port.ts:78`

### servePort

```ts
function servePort(port: PortLike, handler: (request: Request) => Response | Promise<Response>): void
```

Answers the requests `portTransport` sends by building a `Request`,
calling `handler`, and posting the response back. A handler that throws
answers with a 500 problem so the client sees a `ProblemError`.

Source: `packages/client/src/port.ts:127`

## Interfaces

### PortLike

```ts
interface PortLike
```

The port shapes supported: a DOM `MessagePort`, Node's, or Electron's `MessagePortMain`.

- `postMessage(message: unknown): void`: Sends a message to the other end; `portTransport` posts each `PortRequest` through it and `servePort` each `PortResponse`.
- `start?(): void`: Starts delivering messages; called, when present, right after the listener is attached, since a DOM `MessagePort` and Electron's `MessagePortMain` queue messages until it runs.
- `addEventListener?(type: "message", listener: (event: { data: unknown }) => void): void`: Receives messages the `EventTarget` way, as a DOM `MessagePort` does; used in preference to `on` when both exist.
- `on?(type: "message", listener: (event: { data: unknown }) => void): void`: Receives messages the `EventEmitter` way, as Electron's `MessagePortMain` does; used when `addEventListener` is absent, and a port with neither throws a `TypeError`.

Source: `packages/client/src/port.ts:9`

### PortRequest

```ts
interface PortRequest
```

What crosses the port for a request.

- `kind: "zerolith:request"`: Tags the message as a request, so `servePort` ignores other traffic on the port.
- `id: number`: Pairs the request with its response; each `portTransport` numbers its requests from 1.
- `url: string`: The request's absolute URL, from which `servePort` builds the `Request` its handler receives.
- `method: string`: The request method as `Request.method` reports it, such as `POST`.
- `headers: [string, string][]`: The request headers as `[name, value]` pairs with lowercase names, as iterating a `Headers` yields them.
- `body: string | null`: The body as UTF-8 text, or `null` for a `GET` or `HEAD` request or an empty body.

Source: `packages/client/src/port.ts:22`

### PortResponse

```ts
interface PortResponse
```

What crosses the port for a response.

- `kind: "zerolith:response"`: Tags the message as a response, so `portTransport` ignores other traffic on the port.
- `id: number`: The `id` of the request this answers; an answer with no pending request, such as one whose call was aborted, is dropped.
- `status: number`: The status code of the handler's response, or 500 when the handler threw.
- `statusText: string`: The status text of the handler's response, empty when none was set.
- `headers: [string, string][]`: The response headers as `[name, value]` pairs with lowercase names, as iterating a `Headers` yields them.
- `body: string | null`: The body as UTF-8 text, or `null` when it is empty, as for a 204.

Source: `packages/client/src/port.ts:39`