HTTP Header Values

HTTP Header Value Parser

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Parse HTTP header value:

import { hthvParse, hthvParseCommented } from 'http-header-value';

const [contentType] = hthvParse('text/html;charset=utf-8');
contentType.v; // text/html
contentType.p.charset.v; // utf-8

const [product, sysInfo, platform, version] = hthvParseCommented(
  'Mozilla/5.0 (X11; Linux x86_64; rv:70.0) Gecko/20100101 Firefox/70.0',
);

product.v; // Mozilla/5.0
sysInfo.v; // X11
sysInfo.pl[0].v; // Linux x86_64
sysInfo.p.rv.v; // 70.0
platform.v; // Gecko/20100101
version.v; // Firefox/70.0

Supported Headers

See the list of supported HTTP headers and parsers best suited for them

HthvParser

HthvParser is a signature of parser function for HTTP header value.

The httvParse() function is parser with default configuration.

The newHthvParser() function may be used to configure a custom parser. There are also several custom parsers available suitable to parse specific headers (see below).

The parser splits the header value string onto items of type HthvItem.

The value of item is stored in its v property. While its $ property contains a type of item, and may be one of:

  • quoted-string,
  • tagged-string,
  • angle-bracketed-string,
  • date-time,
  • raw (the default).

Multiple Items

Header value may consist of multiple comma- or space- separated items:

Allow: GET, POST, HEAD
Authorization: Basic YWxhZGRpbjpvcGVuc2VzYW1l

That's why the parser returns an array of items.

import { hthvParse } from 'http-header-value';

hthvParse('GET, POST, HEAD').map(item => item.v); // ['GET', 'POST', 'HEAD']
hthvParse('Basic YWxhZGRpbjpvcGVuc2VzYW1l').map(item => item.v); // ['Basic', 'YWxhZGRpbjpvcGVuc2VzYW1l'];

Item Parameters

Each item may have a semicolon-separated parameters. Each parameter may have a name. Parameter name should be a valid token, while its value is separated from the name by = sign, or by : sign within comments.

Accept: text/html, application/xhtml+xml, application/xml;q=0.9, image/webp, */*;q=0.8
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:70.0) Gecko/20100101 Firefox/70.0

Parameters are available via the p property of HthvItem that contains a parameter map. And via pl property that contains an array of all parameters.

Each parameter is represented as HthvItem too. Parameter name is available from its n property.

import { hthvParse, hthvParseCommented } from 'http-header-value';

hthvParse('text/html, application/xhtml+xml, application/xml;q=0.9, image/webp, */*;q=0.8').map(({ v, p: { q } }) => ({
  contentType: v,
  weight: q ? parseFloat(q.v) : 1.0,
}));
//  [
//    { contentType: 'text/html', weight: 1 },
//    { contentType: 'application/xhtml+xml', weight: 1 },
//    { contentType: 'application/xml', weight: 0.9 },
//    { contentType: 'image/webp', weight: 1 },
//    { contentType: '*/*', weight: 0.8 }
//  ]

const [, comment] = hthvParseCommented(`Mozilla/5.0 (X11; Linux x86_64; rv:70.0) Gecko/20100101 Firefox/70.0`);
comment.pl.map(({ n, v }) => (n ? `${n}=${v}` : v)); // [ 'Linux x86_64', 'rv=70.0' ]

Item itself can be a name/value pair.

Cookie: PHPSESSID=298zf09hf012fh2

The parser correctly recognizes that.

import { hthvParse } from 'http-header-value';

hthvParse('PHPSESSID=298zf09hf012fh2'); // { n: 'PHPSESSID', v: '298zf09hf012fh2' }

Quoted String

Values can be enclosed into double quotes. This works both for item values and for parameters.

Clear-Site-Data: "cache"
Public-Key-Pins: pin-sha256="M8HztCzM3elUxkcjR2S5P4hhyBNf6lHkmjAHKhpGPWE="; max-age=5184000; includeSubDomains; report-uri="https://www.example.org/hpkp-report"

The returned item contains the value unquoted and unescaped. The type of such item is quoted-string.

import { hthvParse } from 'http-header-value';

hthvParse('"cache"')[0]; // { $: 'quoted-string', v: 'cache' }

const [pin] = hthvParse(
  'pin-sha256="M8HztCzM3elUxkcjR2S5P4hhyBNf6lHkmjAHKhpGPWE="; ' +
    'max-age=5184000; ' +
    'includeSubDomains; ' +
    'report-uri="https://www.example.org/hpkp-report"',
);
pin.v; // { $: 'quoted-string', n: 'pin-sha256', v: 'M8HztCzM3elUxkcjR2S5P4hhyBNf6lHkmjAHKhpGPWE=' }
pin.p['report-url']; // { $: 'quoted-string', n: 'report-uri', v: 'https://www.example.org/hpkp-report' }

Tagged String

Some headers have special syntax that allows to prepend a quoted string with a tag:

ETag: W/"0815"

The parser recognizes such item value (but not the parameter ones!) as HthvItem with type tagged-string, and places the tag into its t property, and unquoted string - into its v property.

import { hthvParse } from 'http-header-value';

hthvParse('W/"0815"')[0]; // { $: 'tagged-string', t: 'W/', v: '0815' }

Angle brackets

Some headers use angle brackets to enclose strings with special symbols. E.g. URLs:

Link: <https://example.com/index.html?mode=preconnect>; rel="preconnect"

The parser recognizes such item or parameter value as HthvItem with type angle-bracketed-string and value without brackets. Escape sequences not supported inside angle brackets.

import { hthvParse } from 'http-header-value';
hthvParse('<https://example.com/index.html?mode=preconnect>; rel="preconnect"');
// [{
//   $: 'angle-bracketed-string',
//   v: 'https://example.com/index.html?mode=preconnect',
//   p: {
//     rel: { $: 'raw', n: 'rel', v: 'preconnect' }
//   },
//   pl: [{ $: 'raw', n: 'rel', v: 'preconnect' }]
// }]
//

Custom Parsers

There is no standard for HTTP header value syntax. So, there is no way to implement a parser suitable for all headers.

The parser can be configured to understand different header formats. A newHthvParser() function can be used for that. Configuring it properly isn't a simple task. So, the package contains some preconfigured parsers in addition to default one.

Date/Time

Date and time value has special format in headers.

Date: Wed, 21 Oct 2015 07:28:00 GMT
Set-Cookie: id=a3fWa; Expires=Wed, 21 Oct 2015 07:28:00 GMT

Date/time parsing disabled by default. It can be enabled in a custom parser. Then it would recognize date/time values at top-level and as parameter values. It is typically enough to use an hthvParseDT() parser though.

import { hthvParseDT } from 'http-header-value';

hthvParseDT('Wed, 21 Oct 2015 07:28:00 GMT')[0].v; // { $: 'date-time', v: 'Wed, 21 Oct 2015 07:28:00 GMT' }

hthvParseDT('id=a3fWa; Expires=Wed, 21 Oct 2015 07:28:00 GMT')[0].p.Expires;
// { $: 'date-time', n: 'Expires', v: 'Wed, 21 Oct 2015 07:28:00 GMT' }

Comments

Some headers may contain comments enclosed in parentheses.

User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:70.0) Gecko/20100101 Firefox/70.0

Comments parsing disabled by default. It can be enabled in a custom parser. Then it would recognize top-level comments. It is typically enough to use an hthvParseCommented() parser though.

import { hthvParseCommented } from 'http-header-value';

hthvParseCommented('Mozilla/5.0 (X11; Linux x86_64; rv:70.0) Gecko/20100101 Firefox/70.0').map(item => item.v); // ['Mozilla/5.0', 'X11', 'Gecko/20100101', 'Firefox/70.0'];

URIs

URLs may contain ,, ;, '(', ')', and = symbols, that treated specially by default.

Location: http://example.com/matrix;param=(value)?q=some

The httpParseURIs() parser may be used to parse such header values.

import { hthvParseURIs } from 'http-header-value';

hthvParseURIs('http://example.com/matrix;param=(value)?q=some');
// { $: 'raw', v: 'http://example.com/matrix;param=(value)?q=some' };

Cookies

Cookies can be set in response by Set-Cookie header, and in request by Cookie one:

Set-Cookie: id=a3fWa; Expires=Wed, 21 Oct 2015 07:28:00 GMT, SESSIONID=fdkafretercvx
Cookie: id=a3fWa; SESSIONID=fdkafretercvx

The Set-Cookie value can be parsed by hthvParseDT() parser (as it may contain a date/value). While the Cookie value contains cookies semicolon-separated. The hthvParseSemiSep() parser handles this.

import { hthvParseSemiSep } from 'http-header-value';

hthvParseSemiSep('id=a3fWa; SESSIONID=fdkafretercvx').reduce((map, { n, v }) => ({ ...map, [n]: v }), {});
// {
//   id: '3fWa',
//   SESSIONID: 'fdkafretercvx'
// }

Directives

Some headers contain directives. Directives are parameterized items using spaces instead of semicolons to delimit parameters. While semicolons and colons delimit items.

Content-Security-Policy: default-src 'self' http://example.com; connect-src 'none'
Via: HTTP/1.1 GWA, 1.0 fred, 1.1 p.example.net

The hthvParseDirectives() parser supports this format.

import { hthvFlatten, hthvParseDirectives } from 'http-header-value';

const {
  map: { defaultSrc, connectSrc },
} = hthvFlatten(hthvParseDirectives(`default-src 'self' http://example.com; connect-src 'none'`));

defaultSrc.p[0].v; // 'self'
defaultSrc.p[1].v; // http://example.com
connectSrc.p[0].v; // 'none'

Utilities

hthvFlatten()

Flattens HTTP header value items by extracting their parameters.

The result is an item collection containing original items, as well as their parameters.

Recursively places items and their parameters to result map in their original order, and:

  • prefers named items over unnamed ones,
  • prefers original items over their parameters,
  • prefers items added first.
import { hthvFlatten, hthvParseSemiSep } from 'http-header-value';

hthvFlatten(hthvParseSemiSep('id=a3fWa; SESSIONID=fdkafretercvx'));
// {
//   list: [
//     { $: 'raw', n: 'id', v: 'a3fWa' },
//     { $: 'raw', n: 'SESSIONID', v: 'fdkafretercvx' },
//   ],
//   map: {
//     id: { $: 'raw', n: 'id', v: 'a3fWa' },
//     SESSIONID: { $: 'raw', n: 'SESSIONID', v: 'fdkafretercvx' },
//   },
// }

hthvEscapeQ()

Escapes a string to be included into quoted-string within HTTP header value.

Replaces \ with \, and " with \".

import { hthvExcapeQ } from 'http-header-value';

const realm = 'Access to the "Site"';
const wwwAuthenticate = `WWW-Authenticate: Basic realm="${hthvExcapeQ(realm)}"`;
// WWW-Authenticate: Basic realm="Access to the \"Site\""

hthvEscapeC()

Escapes a string to be included into comment withing HTTP header value.

Replaces \ with \, " with \", ( with \(, and ) with \).

According to RFC7230 the sender should not escape a double quote in this case. However, it may be necessary to distinguish between raw double quote and nested quoted-string.

import { hthvExcapeC } from 'http-header-value';

const comment = 'Custom ("quoted") comment';
const customComment = `Custom-Comment: (${hthvExcapeC(comment)})`;
// Custom-Comment: (Custom \(\"quoted\"\) comment)

hthvQuote()

Conditionally encloses HTTP header value or its part into double quotes.

Quotes will be added if delimiter or special character is present in input string, or the input string is empty. Escapes " and `` symbols.

import { hthvQuote } from 'http-header-value';

const forwardedHeader = (forIp: string) => 'Forwarded: For=' + hthvQuote(forIp)};

forwardedHeader('127.0.0.1'); // Forwarded: For=127.0.0.1
forwardedHeader('[2001:db8:cafe::17]:4711'); // Forwarded: For="[2001:db8:cafe::17]:4711"

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