negotiator/lib/mediaType.js

HTTP content negotiation

/**
 * negotiator
 * Copyright(c) 2012 Isaac Z. Schlueter
 * Copyright(c) 2014 Federico Romero
 * Copyright(c) 2014-2015 Douglas Christopher Wilson
 * MIT Licensed
 */

'use strict';

var contentType = require('content-type');
var parseAcceptHeader = require('./accept');

/**
 * Module exports.
 * @public
 */

module.exports = preferredMediaTypes;
module.exports.preferredMediaTypes = preferredMediaTypes;

/**
 * Module variables.
 * @private
 */

function parseAccept(accept) {
  var accepts = parseAcceptHeader(accept);

  for (var i = 0, j = 0; i < accepts.length; i++) {
    var mediaType = formatMediaType(accepts[i], i);
    if (mediaType) accepts[j++] = mediaType;
  }

  accepts.length = j;
  return accepts;
}

/**
 * Format a parsed content type for negotiation.
 * @private
 */

function formatMediaType(parsed, i) {
  var slash = parsed.type.indexOf('/');
  if (slash === -1) return null;

  var q = parsed.parameters.q ? parseFloat(parsed.parameters.q) : 1;

  delete parsed.parameters.q;

  return {
    type: parsed.type.slice(0, slash),
    subtype: parsed.type.slice(slash + 1),
    params: parsed.parameters,
    q: q,
    i: i
  };
}

/**
 * Get the priority of a media type.
 * @private
 */

function getMediaTypePriority(type, accepted, index) {
  var priority = {o: -1, q: 0, s: 0};

  for (var i = 0; i < accepted.length; i++) {
    var spec = specify(type, accepted[i], index);

    if (spec && (priority.s - spec.s || priority.q - spec.q || priority.o - spec.o) < 0) {
      priority = spec;
    }
  }

  return priority;
}

/**
 * Get the specificity of the media type.
 * @private
 */

function specify(type, spec, index) {
  var p = formatMediaType(contentType.parse(type), 0);
  var s = 0;

  if (!p) {
    return null;
  }

  if(spec.type.toLowerCase() == p.type.toLowerCase()) {
    s |= 4
  } else if(spec.type != '*') {
    return null;
  }

  if(spec.subtype.toLowerCase() == p.subtype.toLowerCase()) {
    s |= 2
  } else if(spec.subtype != '*') {
    return null;
  }

  var keys = Object.keys(spec.params);
  if (keys.length > 0) {
    if (keys.every(function (k) {
      return spec.params[k] == '*' || (spec.params[k] || '').toLowerCase() == (p.params[k] || '').toLowerCase();
    })) {
      s |= 1
    } else {
      return null
    }
  }

  return {
    i: index,
    o: spec.i,
    q: spec.q,
    s: s,
  }
}

/**
 * Get the preferred media types from an Accept header.
 * @public
 */

function preferredMediaTypes(accept, provided) {
  // RFC 2616 sec 14.2: no header = */*
  var accepts = parseAccept(accept === undefined ? '*/*' : accept || '');

  if (!provided) {
    // sorted list of all types
    return accepts
      .filter(isQuality)
      .sort(compareSpecs)
      .map(getFullType);
  }

  var priorities = provided.map(function getPriority(type, index) {
    return getMediaTypePriority(type, accepts, index);
  });

  // sorted list of accepted types
  return priorities.filter(isQuality).sort(compareSpecs).map(function getType(priority) {
    return provided[priorities.indexOf(priority)];
  });
}

/**
 * Compare two specs.
 * @private
 */

function compareSpecs(a, b) {
  return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i) || 0;
}

/**
 * Get full type string.
 * @private
 */

function getFullType(spec) {
  return spec.type + '/' + spec.subtype;
}

/**
 * Check if a spec has any quality.
 * @private
 */

function isQuality(spec) {
  return spec.q > 0;
}