ipx

v4.0.0-beta.1

Published

2 days ago

High performance, secure and easy-to-use image optimizer.

0High
0Medium
0Low

pi0

🖼️ IPX

High performance, secure and easy-to-use image optimizer powered by sharp and svgo.

Point IPX at a directory or a list of allowed domains, and every image is available in any size, format and quality straight from its URL:

/w_512,f_webp/photos/buffalo.png

Used by Nuxt Image and Netlify and open to everyone!

[!NOTE] This is the active development branch for IPX v4. Check out v3 for v3 docs, and Migration from v3 to v4 if you are upgrading.

Quick Start

Start a server for the images in the current directory with the ipx command:

npx ipx serve --dir ./

Using bun:

bunx ipx serve --dir ./

Then open the printed URL and add modifiers to any image path, for example http://localhost:3000/w_200/buffalo.png.

To embed IPX in your own app instead, see the Programmatic API.

Image URLs

A request URL is a list of modifiers, followed by the id of the source image:

/<modifiers>/<id>

Multiple modifiers are separated by , and their arguments by _. Use _ alone when no modifier is needed.

| URL | Result | | -------------------------------------------------- | ------------------------------------------------------------------------------------------- | | /_/static/buffalo.png | The original image. | | /w_200/static/buffalo.png | Width set to 200, original format (png) kept. | | /f_webp/static/buffalo.png | Format changed to webp, everything else kept as in the source. | | /f_auto/static/buffalo.png | Best format for the client (avif/webp/jpeg), negotiated from the browser's accept header. | | /s_200x200,fit_contain,f_webp/static/buffalo.png | Resized to fit inside 200x200px on a background canvas and converted to webp. |

The URL style is configurable, see Custom URL Style.

Modifiers

Modifier arguments are separated with _ and validated before they reach sharp. Invalid input is rejected with a 400 IPX_INVALID_MODIFIER_ARG (or 400 IPX_MISSING_MODIFIER_ARG for a required argument) instead of failing the request. Some arguments can only be validated by libvips once it runs, which happens after the whole pipeline is set up; those surface as a 400 IPX_INVALID_MODIFIER. Trailing arguments may be omitted to keep the sharp default, except where noted.

Colours (background, tint) accept any colour sharp understands: hex (f00, ff0000, ff000080) with an optional leading # — which cannot be used inside a URL path, so it may be dropped — or a CSS colour name (red). Boolean arguments accept true / false as well as the shorter 1 / 0.

Programmatic API

Create an IPX instance with createIPX(), then either serve it directly or mount it as a handler in your own app.

Example: Using built-in server

import { serveIPX, createIPX, ipxFSStorage, ipxHttpStorage } from "ipx";

const ipx = createIPX({
  storage: ipxFSStorage({ dir: "./public" }),
  httpStorage: ipxHttpStorage({ domains: ["picsum.photos"] }),
  alias: { "/picsum": "https://picsum.photos" },
});

// http://localhost:3000/w_512/picsum/1000
serveIPX(ipx);

Example: Using with h3

import { H3, serve } from "h3";

import {
  createIPX,
  ipxFSStorage,
  ipxHttpStorage,
  createIPXFetchHandler,
} from "ipx";

const ipx = createIPX({
  storage: ipxFSStorage({ dir: "./public" }),
  httpStorage: ipxHttpStorage({ domains: ["picsum.photos"] }),
  alias: { "/picsum": "https://picsum.photos" },
});

const app = new H3();

app.mount("/ipx", createIPXFetchHandler(ipx));

// http://localhost:3000/ipx/w_512/picsum/1000
serve(app);

Example: Using with express

import Express from "express";

import {
  createIPX,
  ipxFSStorage,
  ipxHttpStorage,
  createIPXNodeHandler,
} from "ipx";

import type { RequestHandler } from "express";

const ipx = createIPX({
  storage: ipxFSStorage({ dir: "./public" }),
  httpStorage: ipxHttpStorage({ domains: ["picsum.photos"] }),
  alias: { "/picsum": "https://picsum.photos" },
});

const app = Express();

app.use("/ipx", createIPXNodeHandler(ipx) as RequestHandler);

// http://localhost:3000/ipx/w_512/picsum/1000
app.listen(3000, () => {
  console.log("Server is running on http://localhost:3000");
});

Config

Every option can also be set universally with an IPX_* environment variable, which is how the CLI is configured. Explicit options win over the environment.

General

| Option | Environment variable | Default | Description | | -------------------- | -------------------------- | ------- | --------------------------------------------------------- | | alias | IPX_ALIAS | {} | Map URL prefixes to other prefixes or remote origins. | | maxOutputDimension | IPX_MAX_OUTPUT_DIMENSION | 8192 | Maximum width and height (in pixels) of the output image. |

Requested width, height and resize dimensions are clamped to maxOutputDimension, preserving the requested aspect ratio, and extend edges are clamped so the extended canvas stays within it. This bounds how much memory a single request can allocate: sharp only limits the input size, so without it /enlarge,s_20000x20000/image.jpg (or /extend_10000_10000_10000_10000/image.jpg) allocates gigabytes from a small source image. Set to false to disable, which is only safe when modifiers come from a trusted source.

Filesystem source (`ipxFSStorage`)

Enabled by default with the CLI only.

| Option | Environment variable | Default | Description | | ------------------------- | ----------------------------------- | ----------------------- | ------------------------------------------------------ | | dir | IPX_FS_DIR | . (current directory) | Directory (or directories) files are served from. | | maxAge | IPX_FS_MAX_AGE | 60 (via maxAge) | cache-control max-age, in seconds, for served files. | | allowSymlinksOutsideDir | IPX_FS_ALLOW_SYMLINKS_OUTSIDE_DIR | false | Allows symlinks inside dir to resolve outside of it. |

HTTP(s) source (`ipxHttpStorage`)

Enabled by default with the CLI only.

| Option | Environment variable | Default | Description | | ----------------- | ---------------------------- | ------- | --------------------------------------------------------------- | | domains | IPX_HTTP_DOMAINS | [] | Allowlist of hostnames images can be fetched from. | | maxAge | IPX_HTTP_MAX_AGE | 300 | | | fetchOptions | IPX_HTTP_FETCH_OPTIONS | {} | Passed to fetch(). | | allowAllDomains | IPX_HTTP_ALLOW_ALL_DOMAINS | false | Disables the allowlist. Unsafe on a public server. | | blockPrivateIPs | IPX_HTTP_BLOCK_PRIVATE_IPS | false | Rejects hosts that are, or resolve to, a non-public IP address. |

Only http: and https: URLs are allowed (anything else is rejected with 403 IPX_FORBIDDEN_PROTOCOL), and redirects are followed only within the allowlist, up to 3 hops: each redirect target is re-validated and a redirect to a host that is not listed is rejected with 403 IPX_FORBIDDEN_HOST (502 IPX_TOO_MANY_REDIRECTS beyond 3 hops). Previously redirects were followed blindly, which let an allowlisted host with an open redirect bounce IPX to internal addresses such as the cloud metadata service (SSRF). If an allowlisted host redirects to a CDN, add the CDN hostname to the allowlist as well. Redirect re-validation is skipped when allowAllDomains is enabled without blockPrivateIPs (nothing to validate) or when redirect is explicitly set in fetchOptions.

Blocking private IP addresses

The allowlist matches hostnames, not addresses, so an allowlisted host whose DNS record points at 127.0.0.1, 169.254.169.254 or an RFC1918 address is fetched like any other. That is intended — allowlisted domains are trusted — but blockPrivateIPs: true adds a second line of defense for setups where the allowlist is broad (or allowAllDomains is on):

ipxHttpStorage({ domains: ["cdn.example.com"], blockPrivateIPs: true });

The host of the requested URL and of every redirect hop must be a public address. IP literals are checked directly, hostnames are resolved with the OS resolver (dns.lookup, so /etc/hosts counts) and all returned addresses must be public. Loopback, 0.0.0.0/8, RFC1918, CGNAT (100.64.0.0/10), link-local (169.254.0.0/16, fe80::/10), unique-local (fc00::/7), multicast, reserved/test ranges and the IPv4-mapped/compatible IPv6 forms of all of them (::ffff:127.0.0.1 and friends) are rejected with 403 IPX_FORBIDDEN_IP. A host that cannot be resolved is a 502 IPX_DNS_LOOKUP_FAILED, and a runtime without node:net/node:dns a 500 IPX_IP_CHECK_UNAVAILABLE — the check fails closed rather than quietly turning itself off.

It is off by default: many deployments legitimately fetch from in-cluster origins (internal object storage, a sidecar, localhost in development), and enabling it by default would break them.

Two limits to be aware of. It does not close the DNS-rebinding window: the name is resolved again when the socket is opened, so a record with a very short TTL can answer with a public address during validation and a private one during the fetch. Closing that requires pinning the validated address on the connection itself, which the plain fetch used here does not expose. And it is not a substitute for the allowlist — a public address that happens to be reachable is still fetched.

SVG Images

SVG images are not processed by sharp. They are sanitized, optimized with svgo and served as image/svg+xml. Input that is not well-formed XML (an unescaped & is a common cause) is rejected with a 400 IPX_INVALID_SVG.

createIPX({
  storage,
  svg: {
    // SVGO config, or `false` to disable optimization
    optimize: { multipass: true },
    // Serve SVG images unsanitized. Only for fully trusted sources!
    unsafeSkipSanitize: false,
  },
});

Optimization

SVGO's preset-default is applied unless you configure plugins yourself. Output is always a re-serialized document, never byte-identical to the source: ids are renamed, elements that are neither visible nor referenced within the same file are dropped, shapes are converted to paths and <style> rules are inlined.

That is fine for images used as <img src> or as CSS backgrounds, but it can break consumers that reach into the document:

Sprite sheets: a <symbol id="icon"> with no <use> in the same file is removed, so <use href="/sprite.svg#icon"> renders nothing.
References by id from outside the file, since ids are renamed (icon-home becomes a).
Selectors in a host page that inlines the SVG, since <rect> becomes <path> and class-based rules are inlined.

Use svg: { optimize: false } to sanitize without optimizing, or keep optimization with the structural plugins disabled (about 1% larger output for typical icons):

createIPX({
  storage,
  svg: {
    optimize: {
      plugins: [
        {
          name: "preset-default",
          params: {
            overrides: { cleanupIds: false, removeHiddenElems: false },
          },
        },
      ],
    },
  },
});

Sanitization

SVG documents can carry active content, so IPX always sanitizes them before serving. Sanitization is independent of optimization: svg: { optimize: false } only disables SVGO's optimization plugins.

Removed from every SVG:

<script> elements (including namespaced ones such as <svg:script>)
Event handler attributes (any on* attribute)
Embedded foreign documents: <foreignObject>, <iframe>, <embed>, <object>, <base>, <link> and <meta>
Event handler elements: <handler> and <listener>
SMIL animations (<animate>, <animateMotion>, <animateTransform> and <set>) that assign an on* attribute or an unsafe URI, which could otherwise re-introduce a handler after load
URIs (href, xlink:href and src) with a scheme other than http:, https:, mailto:, tel:, ftp: or a non-SVG data:image/* — in particular javascript:, including obfuscated variants using entities or control characters
The <!DOCTYPE> declaration and all processing instructions (<?…?>), which are serialized unescaped and can smuggle markup past an HTML parser

External references are kept. Attributes such as <image href="https://…">, <use href="…">, external fonts and @import inside <style> are preserved, since stripping them would break legitimate images. They are not a script execution vector, but they do allow the SVG to make requests to third-party origins (and thereby leak the viewer's IP address) when rendered as a document. If this matters for your threat model, host such images from a separate origin or block the requests with a Content-Security-Policy.

The bundled server sends content-security-policy: default-src 'none' with successful responses by default, which blocks both script execution and external references in browsers that honor it. Custom servers built on the programmatic API should send the same header, since sanitization cannot cover every future browser behavior on its own.

Sanitization can be disabled with svg: { unsafeSkipSanitize: true }. Only do this when every source is fully trusted: IPX will then serve SVG images with XSS payloads unchanged.

Custom URL Style

The parseURL option accepts a function that extracts the resource id and modifiers from the request URL, allowing any URL style you like. It receives the raw (still percent-encoded) request URL, so it is free to decode it however the URL style requires.

Example: modifiers in the filename (/<id>@@<modifiers>.<format>), which can be preferable when prerendering images for static hosting.

import { createIPXFetchHandler, parseIPXURL } from "ipx";

const handler = createIPXFetchHandler(ipx, {
  parseURL(url) {
    const path = decodeURIComponent(new URL(url).pathname.slice(1));

    const match = path.match(/^(.+)@@(.+)\.([^.]+)$/);
    if (!match) {
      // Not our style, fall back to the default `/<modifiers>/<id>`
      return parseIPXURL(url);
    }

    const [, id = "", modifiersString = "", format = ""] = match;
    const modifiers = Object.fromEntries(
      modifiersString.split(",").map((m) => {
        const [key = "", ...values] = m.split("_");
        return [key, values.join("_")];
      }),
    );

    return { id, modifiers: { ...modifiers, format } };
  },
});

// http://localhost:3000/static/buffalo.png@@s_200x200.webp
// http://localhost:3000/static/buffalo.png@@grayscale,w_200.webp

The parser may be async, and can throw an HTTPError (re-exported from ipx) to reject a request with a specific status code.

Returned values are escaped by IPX, so custom parsers don't need to do it themselves. Note this is not an access check — exactly as with the default URL style, what the resulting id is allowed to resolve to is enforced by the storage layer (ipxFSStorage's directory boundary, ipxHttpStorage's domain allowlist).

Migration from v3 to v4

The server creation APIs have changed. See the Programmatic API section for examples.
The JSON error format has changed from { error: string } to { status, statusText, message }.
The svgo option is now svg.optimize. SVG images are always sanitized, even when optimization is disabled.
SVG optimization now applies SVGO's preset-default unless custom plugins are configured (previously only the configured plugins ran), so SVG output is restructured more than before. See the SVG Images section.

License

MIT