encoding.js 3.4 KB

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  1. /**
  2. * negotiator
  3. * Copyright(c) 2012 Isaac Z. Schlueter
  4. * Copyright(c) 2014 Federico Romero
  5. * Copyright(c) 2014-2015 Douglas Christopher Wilson
  6. * MIT Licensed
  7. */
  8. 'use strict';
  9. /**
  10. * Module exports.
  11. * @public
  12. */
  13. module.exports = preferredEncodings;
  14. module.exports.preferredEncodings = preferredEncodings;
  15. /**
  16. * Module variables.
  17. * @private
  18. */
  19. var simpleEncodingRegExp = /^\s*([^\s;]+)\s*(?:;(.*))?$/;
  20. /**
  21. * Parse the Accept-Encoding header.
  22. * @private
  23. */
  24. function parseAcceptEncoding(accept) {
  25. var accepts = accept.split(',');
  26. var hasIdentity = false;
  27. var minQuality = 1;
  28. for (var i = 0, j = 0; i < accepts.length; i++) {
  29. var encoding = parseEncoding(accepts[i].trim(), i);
  30. if (encoding) {
  31. accepts[j++] = encoding;
  32. hasIdentity = hasIdentity || specify('identity', encoding);
  33. minQuality = Math.min(minQuality, encoding.q || 1);
  34. }
  35. }
  36. if (!hasIdentity) {
  37. /*
  38. * If identity doesn't explicitly appear in the accept-encoding header,
  39. * it's added to the list of acceptable encoding with the lowest q
  40. */
  41. accepts[j++] = {
  42. encoding: 'identity',
  43. q: minQuality,
  44. i: i
  45. };
  46. }
  47. // trim accepts
  48. accepts.length = j;
  49. return accepts;
  50. }
  51. /**
  52. * Parse an encoding from the Accept-Encoding header.
  53. * @private
  54. */
  55. function parseEncoding(str, i) {
  56. var match = simpleEncodingRegExp.exec(str);
  57. if (!match) return null;
  58. var encoding = match[1];
  59. var q = 1;
  60. if (match[2]) {
  61. var params = match[2].split(';');
  62. for (var i = 0; i < params.length; i ++) {
  63. var p = params[i].trim().split('=');
  64. if (p[0] === 'q') {
  65. q = parseFloat(p[1]);
  66. break;
  67. }
  68. }
  69. }
  70. return {
  71. encoding: encoding,
  72. q: q,
  73. i: i
  74. };
  75. }
  76. /**
  77. * Get the priority of an encoding.
  78. * @private
  79. */
  80. function getEncodingPriority(encoding, accepted, index) {
  81. var priority = {o: -1, q: 0, s: 0};
  82. for (var i = 0; i < accepted.length; i++) {
  83. var spec = specify(encoding, accepted[i], index);
  84. if (spec && (priority.s - spec.s || priority.q - spec.q || priority.o - spec.o) < 0) {
  85. priority = spec;
  86. }
  87. }
  88. return priority;
  89. }
  90. /**
  91. * Get the specificity of the encoding.
  92. * @private
  93. */
  94. function specify(encoding, spec, index) {
  95. var s = 0;
  96. if(spec.encoding.toLowerCase() === encoding.toLowerCase()){
  97. s |= 1;
  98. } else if (spec.encoding !== '*' ) {
  99. return null
  100. }
  101. return {
  102. i: index,
  103. o: spec.i,
  104. q: spec.q,
  105. s: s
  106. }
  107. };
  108. /**
  109. * Get the preferred encodings from an Accept-Encoding header.
  110. * @public
  111. */
  112. function preferredEncodings(accept, provided) {
  113. var accepts = parseAcceptEncoding(accept || '');
  114. if (!provided) {
  115. // sorted list of all encodings
  116. return accepts
  117. .filter(isQuality)
  118. .sort(compareSpecs)
  119. .map(getFullEncoding);
  120. }
  121. var priorities = provided.map(function getPriority(type, index) {
  122. return getEncodingPriority(type, accepts, index);
  123. });
  124. // sorted list of accepted encodings
  125. return priorities.filter(isQuality).sort(compareSpecs).map(function getEncoding(priority) {
  126. return provided[priorities.indexOf(priority)];
  127. });
  128. }
  129. /**
  130. * Compare two specs.
  131. * @private
  132. */
  133. function compareSpecs(a, b) {
  134. return (b.q - a.q) || (b.s - a.s) || (a.o - b.o) || (a.i - b.i) || 0;
  135. }
  136. /**
  137. * Get full encoding string.
  138. * @private
  139. */
  140. function getFullEncoding(spec) {
  141. return spec.encoding;
  142. }
  143. /**
  144. * Check if a spec has any quality.
  145. * @private
  146. */
  147. function isQuality(spec) {
  148. return spec.q > 0;
  149. }