examples: add encryption example.

examples/encryption/.eslintignore

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+/build/**

examples/encryption/.eslintrc.cjs

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+module.exports = {
+  env: {
+    browser: true,
+    es2021: true,
+    node: true,
+  },
+  extends: [
+    `eslint:recommended`,
+    `plugin:@typescript-eslint/recommended`,
+    `plugin:prettier/recommended`,
+  ],
+  parserOptions: {
+    ecmaVersion: 2022,
+    requireConfigFile: false,
+    sourceType: `module`,
+    ecmaFeatures: {
+      jsx: true,
+    },
+  },
+  parser: `@typescript-eslint/parser`,
+  plugins: [`prettier`],
+  rules: {
+    quotes: [`error`, `single`],
+    "no-unused-vars": `off`,
+    "@typescript-eslint/no-unused-vars": [
+      `error`,
+      {
+        argsIgnorePattern: `^_`,
+        varsIgnorePattern: `^_`,
+        caughtErrorsIgnorePattern: `^_`,
+      },
+    ],
+  },
+  ignorePatterns: [
+    `**/node_modules/**`,
+    `**/dist/**`,
+    `tsup.config.ts`,
+    `vitest.config.ts`,
+    `.eslintrc.js`,
+  ],
+};

examples/encryption/.gitignore

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+dist
+.env.local

examples/encryption/.prettierrc

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+{
+  "semi": false,
+  "singleQuote": true,
+  "tabWidth": 2,
+  "trailingComma": "es5"
+}

examples/encryption/README.md

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+
+# Encryption example
+
+This is an example of encryption with Electric. It's a React app with a very simple Express API server.
+
+The Electric-specific code is in [`./src/Example.tsx`](./src/Example.tsx). It demonstrates:
+
+- encrypting data before sending to the API server
+- decrypting data after it syncs in through Electric
+
+## Setup
+
+This example is part of the [ElectricSQL monorepo](../..) and is designed to be built and run as part of the [pnpm workspace](https://pnpm.io/workspaces) defined in [`../../pnpm-workspace.yaml`](../../pnpm-workspace.yaml).
+
+Navigate to the root directory of the monorepo, e.g.:
+
+```shell
+cd ../../
+```
+
+Install and build all of the workspace packages and examples:
+
+```shell
+pnpm install
+pnpm run -r build
+```
+
+Navigate back to this directory:
+
+```shell
+cd examples/basic-example
+```
+
+Start the example backend services using [Docker Compose](https://docs.docker.com/compose/):
+
+```shell
+pnpm backend:up
+```
+
+Now start the dev server:
+
+```shell
+pnpm dev
+```
+
+Open [localhost:5173]http://localhost:5173] in your web browser. When you add items, the plaintext is encrypted before it leaves the app. You can see the ciphertext in Postgres, e.g.:
+
+```console
+$ psql "postgresql://postgres:password@localhost:54321/electric"
+psql (16.4)
+Type "help" for help.
+
+electric=# select * from items;
+                  id                  |          ciphertext          |        iv
+--------------------------------------+------------------------------+------------------
+ 491b2654-5714-48bb-a206-59f87a2dc33c | vDwv3IX5AGXJVi2jNJJDPE25MwiS | 0gwdqHvqiJ8lJqaS
+(1 row)
+```
+
+When you're done, stop the backend services using:
+
+```shell
+pnpm backend:down
+```

examples/encryption/backend/api.js

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+import bodyParser from 'body-parser'
+import cors from 'cors'
+import express from 'express'
+import pg from 'pg'
+
+import { z } from 'zod'
+
+// Connect to Postgres.
+const DATABASE_URL = process.env.DATABASE_URL || 'postgresql://postgres:password@localhost:54321/electric'
+const DATABASE_USE_SSL = process.env.DATABASE_USE_SSL === 'true' || false
+const pool = new pg.Pool({connectionString: DATABASE_URL, ssl: DATABASE_USE_SSL})
+const db = await pool.connect()
+
+// Expose an HTTP server.
+const PORT = parseInt(process.env.PORT || '3001')
+const app = express()
+app.use(bodyParser.json())
+app.use(cors())
+
+// Validate user input
+const createSchema = z.object({
+  id: z.string().uuid(),
+  ciphertext: z.string(),
+  iv: z.string()
+})
+
+// Expose `POST {data} /items`.
+app.post(`/items`, async (req, res) => {
+  let data
+  try {
+    data = createSchema.parse(req.body)
+  }
+  catch (err) {
+    return res.status(400).json({ errors: err.errors })
+  }
+
+  // Insert the item into the database.
+  const sql = `
+    INSERT INTO items (
+      id,
+      ciphertext,
+      iv
+    )
+    VALUES (
+      $1,
+      $2,
+      $3
+    )
+  `
+
+  const params = [
+    data.id,
+    data.ciphertext,
+    data.iv
+  ]
+
+  try {
+    await db.query(sql, params)
+  }
+  catch (err) {
+    return res.status(500).json({ errors: err })
+  }
+
+  return res.status(200).json({ status: 'OK' })
+})
+
+// Start the server
+app.listen(PORT, () => {
+  console.log(`Server listening at http://localhost:${PORT}`)
+})

examples/encryption/db/migrations/01-create_items_table.sql

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+CREATE TABLE IF NOT EXISTS items (
+  id UUID PRIMARY KEY NOT NULL,
+  ciphertext TEXT NOT NULL,
+  iv TEXT NOT NULL
+);

examples/encryption/index.html

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+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <link rel="icon" type="image/svg+xml" href="/vite.svg" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Web Example - ElectricSQL</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/main.tsx"></script>
+  </body>
+</html>

examples/encryption/package.json

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+{
+  "name": "@electric-examples/encryption",
+  "private": true,
+  "version": "0.0.1",
+  "author": "ElectricSQL",
+  "license": "Apache-2.0",
+  "type": "module",
+  "scripts": {
+    "backend:up": "PROJECT_NAME=basic-example pnpm -C ../../ run example-backend:up && pnpm db:migrate",
+    "backend:down": "PROJECT_NAME=basic-example pnpm -C ../../ run example-backend:down",
+    "db:migrate": "dotenv -e ../../.env.dev -- pnpm exec pg-migrations apply --directory ./db/migrations",
+    "dev": "concurrently \"vite\" \"node backend/api.js\"",
+    "build": "vite build",
+    "format": "eslint . --ext ts,tsx --fix",
+    "stylecheck": "eslint . --ext ts,tsx --report-unused-disable-directives --max-warnings 0",
+    "preview": "vite preview",
+    "typecheck": "tsc --noEmit"
+  },
+  "dependencies": {
+    "@electric-sql/react": "workspace:*",
+    "base64-js": "^1.5.1",
+    "body-parser": "^1.20.2",
+    "cors": "^2.8.5",
+    "express": "^4.19.2",
+    "pg": "^8.12.0",
+    "react": "^18.3.1",
+    "react-dom": "^18.3.1",
+    "uuid": "^10.0.0",
+    "zod": "^3.23.8"
+  },
+  "devDependencies": {
+    "@databases/pg-migrations": "^5.0.3",
+    "@types/react": "^18.3.3",
+    "@types/react-dom": "^18.3.0",
+    "@types/uuid": "^10.0.0",
+    "@vitejs/plugin-react": "^4.3.1",
+    "concurrently": "^8.2.2",
+    "dotenv": "^16.4.5",
+    "eslint": "^8.57.0",
+    "typescript": "^5.5.3",
+    "vite": "^5.3.4"
+  }
+}

examples/encryption/public/robots.txt

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+# https://www.robotstxt.org/robotstxt.html
+User-agent: *
+Disallow:

examples/encryption/src/App.css

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+.App {
+  text-align: center;
+}
+
+.App-logo {
+  height: 64px;
+  pointer-events: none;
+  margin-top: min(40px, 5vmin);
+  margin-bottom: min(20px, 4vmin);
+}
+
+.App-header {
+  background-color: #1c1e20;
+  min-height: 100vh;
+  display: flex;
+  flex-direction: column;
+  align-items: top;
+  justify-content: top;
+  font-size: calc(10px + 2vmin);
+  color: white;
+}
+
+.App-link {
+  color: #61dafb;
+}

examples/encryption/src/App.tsx

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+import logo from './assets/logo.svg'
+import './App.css'
+import './style.css'
+
+import { Example } from './Example'
+
+export default function App() {
+  return (
+    <div className="App">
+      <header className="App-header">
+        <img src={logo} className="App-logo" alt="logo" />
+        <Example />
+      </header>
+    </div>
+  )
+}

examples/encryption/src/Example.css

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+.controls {
+  margin-bottom: 1.5rem;
+}
+
+.button {
+  display: inline-block;
+  line-height: 1.3;
+  text-align: center;
+  text-decoration: none;
+  vertical-align: middle;
+  cursor: pointer;
+  user-select: none;
+  width: calc(15vw + 100px);
+  margin-right: 0.5rem !important;
+  margin-left: 0.5rem !important;
+  border-radius: 32px;
+  text-shadow: 2px 6px 20px rgba(0, 0, 0, 0.4);
+  box-shadow: rgba(0, 0, 0, 0.5) 1px 2px 8px 0px;
+  background: #1e2123;
+  border: 2px solid #229089;
+  color: #f9fdff;
+  font-size: 16px;
+  font-weight: 500;
+  padding: 10px 18px;
+}
+
+.item {
+  display: block;
+  line-height: 1.3;
+  text-align: center;
+  vertical-align: middle;
+  width: calc(30vw - 1.5rem + 200px);
+  margin-right: auto;
+  margin-left: auto;
+  border-radius: 9px;
+  border: 1px solid #D0BCFF;
+  background: #1e2123;
+  color: #D0BCFF;
+  font-size: 13px;
+  padding: 10px 18px;
+}
+
+form {
+  border-top: 0.5px solid rgba(227, 227, 239, 0.32);
+  width: calc(30vw - 1.5rem + 200px);
+  margin: 20px auto;
+  padding: 20px 0;
+}
+
+form input[type=text] {
+  padding: 12px 18px;
+  margin-bottom: 18px;
+  background: #1e2123;
+  border: 1px solid rgba(227, 227, 239, 0.92);
+  border-radius: 9px;
+  color: #f5f5f5;
+  outline: none;
+  font-size: 14px;
+  display: block;
+  text-align: center;
+  width: calc(30vw - 1.5rem + 160px);
+  margin-right: auto;
+  margin-left: auto;
+}
+
+form input[type=text]::placeholder {
+  color: rgba(227, 227, 239, 0.62);
+}
+
+form button[type=submit] {
+  background: #D0BCFF;
+  border: none;
+  padding: 8px 20px;
+  border-radius: 9px;
+  color: #1e2123;
+  font-size: 15px;
+  font-weight: 500;
+  cursor: pointer;
+}