@kikobeats/set-content-type

Set the response content-type based on the payload bytes.

Some upstreams (e.g. S3/CloudFront origins) stream a response without a content-type header. When you proxy those bytes, the browser can't tell it's an image and renders it as raw text — worse if you send x-content-type-options: nosniff.

This module fixes that: pipe the payload through it and, only when the response doesn't already have a content-type, it detects the type from the first bytes (via file-type) and sets it on the response before anything is written.

Install

$ npm install @kikobeats/set-content-type --save

Usage

Insert it between your upstream and the response:

const setContentType = require('@kikobeats/set-content-type')

server.on('request', (req, res) => {
  upstream.pipe(setContentType(res))
})

The returned stream is already wired to res, so you only pipe once. If the upstream already provided a content-type, it is left untouched.

API

setContentType(res)

res

Required Type: http.ServerResponse

The outgoing response whose content-type should be set when missing.

It returns a writable stream already piped to res — pipe your upstream into it and you are done.

The header is always set before the first byte is written to res, and an existing content-type is never overridden. Detection is delegated to fileTypeStream, which holds a sample before deciding, so a signature split across chunk boundaries is still recognized and a container reports its real type rather than its envelope — a .docx as a Word document rather than application/zip.

Buffering is bounded by that sample and nothing beyond it is held, so a body smaller than the sample reaches res when the upstream ends. Nothing is sampled at all when res already has a content-type.

If detection itself fails, the error surfaces on the returned stream and res is destroyed rather than sent a body the sample has already eaten into.

The header is not set when:

• res already has a content-type header.
• the response has already been sent (res.headersSent).
• the payload type can not be recognized.

License

@kikobeats/set-content-type © Kiko Beats, released under the MIT License. Authored and maintained by Kiko Beats with help from contributors.

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