---
name: pikku-rpc
description: 'Use when making internal function-to-function calls within a Pikku app, composing functions, or exposing RPC endpoints. Covers rpc.invoke, rpc.remote, rpc.exposed, and generated RPC client.
TRIGGER when: code uses wire.rpc or expose: true, user asks about calling one Pikku function from another, function composition, or RPC endpoints.
DO NOT TRIGGER when: user asks about HTTP routes (use pikku-http) or addon cross-package calls (use pikku-addon).'
installGroups: [core]
---

# Pikku RPC Wiring

## Agent Operating Procedure

Use this skill as an execution checklist, not reference material.

1. Discover before editing. Prefer OpenCode tools such as `pikku-meta` when available; otherwise run the relevant `pikku meta ... --json` command and inspect only the focused output you need.
2. Identify the source files that own the behavior. Do not start by reading generated output, `.pikku`, `node_modules`, vendored packages, or broad build artifacts.
3. Make the smallest source change that satisfies the task. Keep generated files generated, and avoid hand-editing SDKs, schema output, or typegen.
4. Validate with the narrowest relevant command first, then run `pikku-verify` or `pikku all` when functions, wirings, schemas, or generated clients may have changed.
5. If validation fails, fix the source cause and rerun validation. Do not paper over generated errors by editing generated files.

Call Pikku functions from other Pikku functions internally with full type safety. Use RPC to compose business logic without importing functions directly.

## Before You Start

```bash
pikku info functions --verbose   # See existing functions and which could be called via RPC
pikku info tags --verbose        # Understand project organization
```

See `pikku-concepts` for the core mental model.

## API Reference

### RPC Methods (on `wire.rpc`)

Four ways to call functions via RPC:

| Method                           | Purpose                                   |
| -------------------------------- | ----------------------------------------- |
| `rpc.invoke(name, data)`         | Internal call to any wired function       |
| `rpc.remote(name, data)`         | Remote call via DeploymentService         |
| `rpc.exposed(name, data)`        | Call functions marked with `expose: true` |
| `rpc.startWorkflow(name, input)` | Start a workflow                          |

### Exposed Functions

Mark a function as externally callable via RPC:

```typescript
const greet = pikkuSessionlessFunc({
  title: 'Greet',
  expose: true, // ← callable via rpc.exposed()
  func: async ({}, { name }) => {
    return { message: `Hello, ${name}!` }
  },
})
```

### HTTP RPC Endpoint

Expose all `expose: true` functions over HTTP:

```typescript
wireHTTP({
  route: '/rpc/:rpcName',
  method: 'post',
  auth: false,
  func: rpcCaller,
})
```

## Usage Patterns

### Internal Function Composition

```typescript
const calculateTax = pikkuSessionlessFunc({
  title: 'Calculate Tax',
  func: async ({}, { amount, rate }) => {
    return { tax: amount * rate }
  },
})

const processOrder = pikkuFunc({
  title: 'Process Order',
  func: async ({ db }, { orderId }, { rpc }) => {
    const order = await db.getOrder(orderId)

    // Call another pikku function internally — fully typed
    const { tax } = await rpc.invoke('calculateTax', {
      amount: order.total,
      rate: 0.08,
    })

    return { orderId, total: order.total + tax }
  },
})
```

### When to Use RPC vs Direct Imports

| Approach       | Use When                                                                                     |
| -------------- | -------------------------------------------------------------------------------------------- |
| `rpc.invoke()` | Cross-domain calls, maintaining separation of concerns, function may be in different package |
| Direct import  | Same module, tightly coupled logic, performance critical                                     |

RPC calls go through Pikku's middleware and permission pipeline. Direct imports skip them.

### Generated RPC Client

After `npx pikku prebuild`:

```typescript
import { pikkuRPC } from '.pikku/pikku-rpc.gen.js'

pikkuRPC.setServerUrl('http://localhost:4002')

const result = await pikkuRPC.invoke('calculateTax', {
  amount: 100,
  rate: 0.08,
})

pikkuRPC.setAuthorizationJWT(token)
```

## Complete Example

```typescript
// functions/billing.functions.ts
export const calculateTax = pikkuSessionlessFunc({
  title: 'Calculate Tax',
  func: async ({}, { amount, region }) => {
    const rates = { US: 0.08, EU: 0.2, UK: 0.2 }
    return { tax: amount * (rates[region] || 0) }
  },
})

export const calculateShipping = pikkuSessionlessFunc({
  title: 'Calculate Shipping',
  func: async ({}, { weight, region }) => {
    const base = region === 'US' ? 5 : 15
    return { shipping: base + weight * 0.5 }
  },
})

// functions/orders.functions.ts
export const processOrder = pikkuFunc({
  title: 'Process Order',
  func: async ({ db }, { orderId }, { rpc }) => {
    const order = await db.getOrder(orderId)

    const { tax } = await rpc.invoke('calculateTax', {
      amount: order.total,
      region: order.region,
    })

    const { shipping } = await rpc.invoke('calculateShipping', {
      weight: order.totalWeight,
      region: order.region,
    })

    const finalTotal = order.total + tax + shipping
    await db.updateOrder(orderId, { tax, shipping, finalTotal })

    return { orderId, total: finalTotal, tax, shipping }
  },
})
```
