XyPriss Compressible Check — xypriss-compressible

[!NOTE] Internalized Fork: This module is a strictly typed TypeScript port of the original compressible library. It has been internalized into the XyPriss ecosystem to reduce external dependency surfaces and ensure architectural consistency within XyPriss framework plugins.

Overview

xypriss-compressible determines whether a given Content-Type or MIME type string is worth compressing before sending to the client. It combines an explicit database lookup (mime-db) with a convention-based fallback for types not covered by the database.

Installation

xfpm install xypriss-compressible

Usage

Basic

import compressible from "xypriss-compressible";

compressible("text/html"); // → true
compressible("image/png"); // → false
compressible("application/x-custom"); // → undefined

With a full Content-Type header value

Parameters like charset are automatically stripped before the lookup.

compressible("text/html; charset=utf-8"); // → true
compressible("application/json; charset=utf-8"); // → true

In middleware

import vary from "xypriss-vary";
import compressible from "xypriss-compressible";

function compressionMiddleware(req, res, next) {
  const type = res.getHeader("Content-Type") as string;

  if (type && compressible(type) === true) {
    vary(res, "Accept-Encoding");
    // … apply compression stream …
  }

  next();
}

API

compressible(type)

| Parameter | Type | Description | | --------- | -------- | ------------------------------------------------ | | type | string | A MIME type or full Content-Type header value. |

Returns boolean | undefined:

| Return value | Meaning | | ------------ | ----------------------------------------------------------------------- | | true | The type is compressible. | | false | The type is explicitly not compressible, or type is not a string. | | undefined | Compressibility is unknown — treat as "maybe" in your middleware logic. |

The function never throws. Non-string inputs return false; malformed strings return undefined.

Resolution Order

1. mime-db lookup — if the database entry carries an explicit compressible flag, that value is returned as-is.
2. Convention-based fallback — if the type is absent from the database (or has no compressible flag), the following patterns return true:
   • text/*
   • *+json
   • *+text
   • *+xml
3. Unknown — if neither rule matches, undefined is returned.

Common Values

| MIME type | Result | | -------------------------- | ----------- | | text/html | true | | text/plain | true | | application/json | true | | application/vnd.api+json | true | | application/xml | true | | image/png | false | | image/jpeg | false | | application/octet-stream | false | | video/mp4 | false | | application/x-custom | undefined |

Technical Implementation

• Strict TypeScript port — no runtime dependencies beyond mime-db; full compile-time safety.
• Never throws — non-string inputs return false; malformed strings return undefined. Safe to use as a filter predicate without try/catch.
• Typed mime-db access — the internal MimeDbEntry interface makes the database shape explicit and prevents silent property access on unknown.
• Clear resolution order — db lookup → regexp fallback → undefined; each step is isolated and commented.

History

See HISTORY.md for full release details.

License

Copyright © 2013 Jonathan Ong
Copyright © 2014 Jeremiah Senkpiel
Copyright © 2015 Douglas Christopher Wilson
Copyright © 2026 Nehonix Team
Released under the MIT License.