negotiated

negotiated

This is a low-level utility for correctly parsing the HTTP content negotiation headers. It doesn't interpret the parsed values in any way, except for ensuring that they are syntactically correct.

Installation

npm install --save negotiated

Usage

const negotiated = require('negotiated');

const best = Array.from(negotiated.languages('fr;q=0.4, ja-JP;q=0.2, de-DE;q=0.7, en;q=0.5'))
  .reduce((a, b) => a.weight >= b.weight ? a : b);

console.log(best.language); // => "de-de"

This package exports six functions:

• mediaTypes(): parses the Accept header, emitting { type, params, weight, extensions }
• charsets(): parses the Accept-Charset header, emitting { charset, weight }
• encodings(): parses the Accept-Encoding header, emitting { encoding, weight }
• languages(): parses the Accept-Language header, emitting { language, weight }
• transferEncodings(): parses the TE header, emitting { encoding, params, weight }
• parameters(): parses the params and extensions found above, emitting { key, value }

Each of the exported functions takes a string as the only argument. An iterator is returned, which parses one comma-separated item at a time. If the input string is invalid (according to RFC 7230 or RFC 7231), an error will be thrown mid-iteration.

Examples

Iterating over the Accept-Encoding header

const negotiated = require('negotiated');

for (const { encoding, weight } of negotiated.encodings('gzip;q=0.5, my-custom-encoding;q=1')) {
  if (weight > 0.8) console.log(`${encoding} is desired`);
}

// => "my-custom-encoding is desired"

Parsing media parameters

const negotiated = require('negotiated');

const [{ params }] = Array.from(negotiated.mediaTypes('application/json; CHARSET="utf-8"'));

console.log(Array.from(negotiated.parameters(params))); // => [{ key: 'charset', value: 'utf-8' }]