フロンティアの強化: React の実験的な Taint API への開発者の深い探求

            // app/data/users.js
import { db } from './database';

export async function getUser(userId) {
  const user = await db.user.findUnique({ where: { id: userId } });
  // The 'user' object might look like this:
  // {
  //   id: 'user_123',
  //   name: 'Alice',
  //   email: 'alice@example.com',       // Safe to display
  //   passwordHash: '...',              // EXTREMELY SENSITIVE
  //   apiKey: 'secret_key_...',         // EXTREMELY SENSITIVE
  //   twoFactorSecret: '...',           // EXTREMELY SENSITIVE
  //   internalNotes: 'VIP customer'   // Sensitive business data
  // }
  return user;
}
            

              
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            // app/profile/[id]/page.js (Server Component)
import { getUser } from '@/app/data/users';
import UserProfileCard from '@/app/components/UserProfileCard'; // This is a Client Component

export default async function ProfilePage({ params }) {
  const user = await getUser(params.id);

  // The critical mistake is here:
  return <UserProfileCard user={user} />;
}
            

              
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            // app/components/UserProfileCard.js
'use client';

export default function UserProfileCard({ user }) {
  // This component only needs user.name and user.email
  return (
    <div>
      <h1>{user.name}</h1>
      <p>Email: {user.email}</p>
    </div>
  );
}
            

              
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            // app/data/users.js (Now with tainting)
import { experimental_taintObjectReference } from 'react';
import { db } from './database';

export async function getUser(userId) {
  const user = await db.user.findUnique({ where: { id: userId } });

  if (user) {
    // Taint the object as soon as we get it!
    experimental_taintObjectReference(
      'Security Violation: The full user object should not be passed to the client. ' +
      'Instead, create a sanitized DTO (Data Transfer Object) with only the necessary fields.',
      user
    );
  }

  return user;
}
            

              
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            // app/profile/[id]/page.js (Server Component - NO CHANGE NEEDED HERE)
export default async function ProfilePage({ params }) {
  const user = await getUser(params.id);

  // This line will now cause a server-side error!
  return <UserProfileCard user={user} />;
}
            

              
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            // app/profile/[id]/page.js (Server Component - CORRECTED)
import { getUser } from '@/app/data/users';
import UserProfileCard from '@/app/components/UserProfileCard';

export default async function ProfilePage({ params }) {
  const user = await getUser(params.id);

  // If user not found, handle it (e.g., notFound() in Next.js)
  if (!user) { ... }

  // Create a new, clean object for the client
  const userForClient = {
    name: user.name,
    email: user.email
  };

  // This is safe because userForClient is a brand new object
  // and its reference is not tainted.
  return <UserProfileCard user={userForClient} />;
}
            

              
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            // app/config.js (Server-only module)
import { experimental_taintUniqueValue } from 'react';

export const serverConfig = {
  DATABASE_URL: process.env.DATABASE_URL,
  API_SECRET_KEY: process.env.API_SECRET_KEY,
  PUBLIC_API_ENDPOINT: 'https://api.example.com/public'
};

// Taint the secret key immediately after loading it
if (serverConfig.API_SECRET_KEY) {
  experimental_taintUniqueValue(
    'CRITICAL: API_SECRET_KEY must never be exposed to the client.',
    serverConfig, // The object holding the value
    serverConfig.API_SECRET_KEY // The value itself
  );
}

            

              
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            // app/some-page/page.js (Server Component)
import { serverConfig } from '@/app/config';
import SomeClientComponent from '@/app/components/SomeClientComponent';

export default function SomePage() {
  // Developer creates an object for the client
  const clientProps = {
    endpoint: serverConfig.PUBLIC_API_ENDPOINT,
    // The mistake:
    apiKey: serverConfig.API_SECRET_KEY
  };

  // This will throw an error!
  return <SomeClientComponent config={clientProps} />;
}
            

              
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            // app/lib/security.js
import { experimental_taintObjectReference } from 'react';

const SENSITIVE_OBJECT_MESSAGE = 
  'Security Violation: This object contains sensitive server-only data and cannot be passed to a client component. ' +
  'Please create a sanitized DTO for client use.';

export function taintSensitiveObject(obj) {
  if (process.env.NODE_ENV === 'development' && obj) {
    experimental_taintObjectReference(SENSITIVE_OBJECT_MESSAGE, obj);
  }
  return obj;
}

// Now use it in your data fetchers
import { db } from './database';
import { taintSensitiveObject } from './security';

export async function getFullUser(userId) {
  const user = await db.user.findUnique({ where: { id: userId } });
  return taintSensitiveObject(user);
}
            

              
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            // app/config/server-env.js
import { experimental_taintUniqueValue } from 'react';

const env = {
  STRIPE_SECRET_KEY: process.env.STRIPE_SECRET_KEY,
  SENDGRID_API_KEY: process.env.SENDGRID_API_KEY,
  // ... other secrets
};

function taintEnvSecrets() {
  for (const key in env) {
    const value = env[key];
    if (value) {
      experimental_taintUniqueValue(
        `Security Alert: Environment variable ${key} cannot be sent to the client.`, 
        env, 
        value
      );
    }
  }
}

taintEnvSecrets();

export default env;
            

              
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            // app/lib/auth.js
import { getSession } from 'next-auth/react'; // Example library
import { taintSensitiveObject } from './security';

export async function getCurrentUserSession() {
  const session = await getSession(); // This might contain sensitive tokens
  return taintSensitiveObject(session);
}
            

              
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