@pixengine/middleware-jit

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On-demand (Just-In-Time) image transformation middleware for PixEngine. This package allows you to generate image variants on-the-fly when they are requested by the user, rather than pre-generating all possible variants at upload time.

🌟 Features

• Lazy Generation: Create variants only when they are first accessed.
• Storage Backed: Generated variants are saved to your storage adapter (S3, Local, etc.) for future hits.
• Secure: URL signing mechanism to prevent Denial of Service (DoS) attacks via resource exhaustion.
• Seamless Integration: Works with existing PixEngine policies and adapters.

📦 Installation

npm install @pixengine/middleware-jit
# or
pnpm add @pixengine/middleware-jit

🚀 Usage

Basic Setup (Express Example)

import express from "express";
import { createJitMiddleware } from "@pixengine/middleware-jit";
import { SharpEngine } from "@pixengine/adapter-engine-sharp";
import { LocalStorage } from "@pixengine/adapter-storage-local";

const app = express();

const jitMiddleware = createJitMiddleware({
  secret: "your-secure-signing-secret",
  engine: new SharpEngine(),
  storage: new LocalStorage({ baseDir: "./uploads" }),
  // Define allowed transformations or policy
  policy: (ctx) => {
    // Return allowed variant/decision for the requested context
    return {
      // ...
    };
  },
});

// Mount at a specific path
app.use("/images", jitMiddleware);

app.listen(3000);

🔒 Security

JIT transformation endpoints are vulnerable to abuse if not secured. This middleware uses HMAC signatures to verify that a requested transformation is authorized.

URLs must be signed using the provided utility:

import { signUrl } from "@pixengine/middleware-jit";

const url = signUrl({
  path: "/images/original.jpg",
  modifiers: { width: 400, format: "webp" },
  secret: "your-secure-signing-secret",
});
// -> /images/original.jpg?w=400&f=webp&s=abc123signature...

License

MIT © PixEngine Team