---
title: HTTP
description: Serve your procedures over HTTP and call them from a typed client.
---

`handle(router, opts?)` from `tacho/transport/fetch` is `(Request) => Promise<Response>`. POST only. Puts `req` on context. CORS is not built in - wrap `handle()`.

```ts twoslash
// @noErrors
import { serve } from "srvx";
import { handle } from "tacho/transport/fetch";
import { tacho } from "tacho";

const rpc = tacho();
const router = rpc({ ping: rpc.run(() => "pong" as const) });
// ---cut---
serve({
  fetch: handle(router, {
    path: "/rpc",
    createContext: (req) => ({
      user: req.headers.get("x-user") ?? undefined,
    }),
    onError: (err, req) => console.error(req.url, err),
  }),
});
```

| option          |                                                           |
| --------------- | --------------------------------------------------------- |
| `path`          | Other paths → 404.                                        |
| `createContext` | Merged onto `{ req }`. Throw → JSON-RPC `INTERNAL_ERROR`. |
| `onError`       | Called when `createContext` or the stream throws.         |
| `maxBodySize`   | Max request body in bytes. Default: `1_048_576` (1 MB).   |
| `maxBatchSize`  | Max items in a batch request. Default: `20`.              |
| `serializer`    | Custom serializer (e.g. `superjson`).                     |

Non-POST → `405` + `Allow: POST`. Notification (no `id`) → `204`.

`createClient` from `tacho/client/http` is a typed proxy over POST.

```ts twoslash
import { createClient } from "tacho/client/http";
import { tacho } from "tacho";

const rpc = tacho();
const router = rpc({ ping: rpc.run(() => "pong" as const) });
type Router = typeof router;
const token = "secret";
// ---cut---
const client = createClient<Router>({
  url: "http://localhost:3000",
  headers: () => ({ authorization: `Bearer ${token}` }),
  signal: AbortSignal.timeout(5_000),
});

await client.ping();
await client.ping(undefined, { signal: AbortSignal.timeout(1_000) });
```

| option       |                                                            |
| ------------ | ---------------------------------------------------------- |
| `url`        | POST target.                                               |
| `headers`    | Object or `() => HeadersInit \| Promise<HeadersInit>`.     |
| `signal`     | Default abort. Per-call: `client.ping(input, { signal })`. |
| `fetch`      | Custom `fetch`.                                            |
| `serializer` | Custom serializer.                                         |

`async function*` over this transport is [SSE](/tacho/sse-streaming). `File` / `Blob` in params or returns is [Files](/tacho/files).