allow custom hashingSteam

index.js

@@ -18,6 +18,7 @@ var crypto = require('crypto');
  *    when hashing to distinguish between types
  *  - `unorderedArrays` {true|*false} Sort all arrays before hashing
  *  - `unorderedSets` {*true|false} Sort `Set` and `Map` instances before hashing
+ *  - `hashingStream` optional stream that is used in place of the native hashing stream
  *  * = default
  *
  * @param {object} object value to hash
@@ -74,6 +75,7 @@ function applyDefaults(object, options){
   options.unorderedObjects = options.unorderedObjects === false ? false : true; // default to true
   options.replacer = options.replacer || undefined;
   options.excludeKeys = options.excludeKeys || undefined;
+  options.hashingStream = options.hashingStream || undefined;
 
   if(typeof object === 'undefined') {
     throw new Error('Object argument required.');
@@ -113,7 +115,9 @@ function isNativeFunction(f) {
 function hash(object, options) {
   var hashingStream;
 
-  if (options.algorithm !== 'passthrough') {
+  if (options.hashingStream) {
+    hashingStream = options.hashingStream;
+  } else if (options.algorithm !== 'passthrough') {
     hashingStream = crypto.createHash(options.algorithm);
   } else {
     hashingStream = new PassThrough();

readme.markdown

@@ -46,6 +46,7 @@ Generate a hash from any object or type.  Defaults to sha1 with hex encoding.
    `hash(new Set([1, 2])) == hash(new Set([2, 1]))` return `true`. default: true
 *  `unorderedObjects` {true|false} Sort objects before hashing, i.e. make `hash({ x: 1, y: 2 }) === hash({ y: 2, x: 1 })`. default: true
 *  `excludeKeys` optional function for exclude specific key(s) from hashing, if returns true then exclude from hash. default: include all keys
+*  `hashingStream` optional stream that is used in place of the native hashing stream
 
 ## hash.sha1(value);
 Hash using the sha1 algorithm.
@@ -147,6 +148,14 @@ hash(michael, { algorithm: 'md5', encoding: 'base64' });
 // djXaWpuWVJeOF8Sb6SFFNg==
 hash(bob, { algorithm: 'md5', encoding: 'base64' });
 // lFzkw/IJ8/12jZI0rQeS3w==
+
+/***
+ * use custom hashStream
+ */
+const secret = 'abcdefg';
+const hashStream = crypto.createHmac('sha256', secret);
+hash(bob, { hashStream });
+// 
 ```
 
 ## Legacy Browser Support

test/index.js

@@ -287,4 +287,11 @@ describe('hash', function() {
       assert.equal(ha, hb, 'Hashing should not respect the order of Set entries');
     });
   }
+
+  it('custom hashingStream works', function() {
+    var ha;
+    ha = hash({a: 1, b: 4}, { hashingStream: crypto.createHmac('sha256', '123456') });
+
+    assert.equal(ha, '550abb83536475fc08989a28b4a9b3be220048dd0610affadf4d8829360fbea1', 'Custom hashingSteam should be used');
+  });
 });