@insler/rpc/host

The server side. Host.create(contract, handlers, transport, options?) registers validated handlers on a HostTransport and returns a HostInstance ({ stop() }).

import { Contract } from '@insler/rpc/contract';
import { Host } from '@insler/rpc/host';

const handlers: Contract.Handlers<typeof Accounts> = {
  getBalance: async ({ identity }, { accountId }) => {
    // context first (when the method has context schemas), then input
    return { balance: 42 };
  },
  watchBalance: async function* ({ identity }, { accountId }) {
    yield { balance: 42 };
  },
};

const host = await Host.create(Accounts, handlers, hostTransport);
// ... later
await host.stop();

What the host guarantees

• Validation. Inputs and outputs are validated against the contract’s zod schemas; failures surface as the reserved __validation__ error.
• Context extraction. Per-request context is pulled from request metadata via a Propagator (JSON by default, options.propagator to override).
• Error normalization. A handler throw carrying a _tag becomes that typed contract error; anything else is stripped to __unknown__ — internal details never leak to callers.
• Completeness. Missing a handler for any contract method throws at Host.create time, not at first call.

Handler shape

Handlers receive (context?, input?) — the context argument is present only when the method or contract declares context schemas, and the input argument is absent for void input. Throw { _tag, payload } for contract errors.

Middleware

options.middleware wraps handlers with a composed chain (composeMiddleware); validation, context extraction, and exception safety stay inside the envelope. Coverage today is partial: unary and serverStream handlers are wrapped, clientStream and duplex are registered without middleware until streaming middleware coverage lands.

Secondary entrypoints

• @insler/rpc/host/test — TestHost.pair, the default integration seam.
• @insler/rpc/host/dev — logging middleware and handler validation for development.