feat(hex): utility function for getting hex version of digest

Author: zkat

README.md

@@ -21,6 +21,7 @@ Integrity](https://w3c.github.io/webappsec/specs/subresourceintegrity/) hashes.
     * [`Integrity#concat`](#integrity-concat)
     * [`Integrity#toString`](#integrity-to-string)
     * [`Integrity#pickAlgorithm`](#integrity-pick-algorithm)
+    * [`IntegrityMetadata#hexDigest`](#integrity-metadata-hex-digest)
   * Integrity Generation
     * [`fromData`](#from-data)
     * [`fromStream`](#from-stream)
@@ -215,6 +216,17 @@ may intentionally deprioritize algorithms with known vulnerabilities.
 ssri.parse('sha1-WEakDigEST sha512-yzd8ELD1piyANiWnmdnpCL5F52f10UfUdEkHywVZeqTt0ymgrxR63Qz0GB7TKPoeeZQmWCaz7T1').pickAlgorithm() // sha512
 ```
 
+#### <a name="integrity-metadata-hex-digest"></a> `> IntegrityMetadata#hexDigest() -> String`
+
+Called on an *individual* `IntegrityMetadata` object, will convert its `digest`
+to a hex representation of the base64 data.
+
+##### Example
+
+```javascript
+ssri.parse('sha1-deadbeef', {single: true}).hexDigest() // '75e69d6de79f'
+```
+
 #### <a name="from-data"></a> `> ssri.fromData(data, [opts]) -> Integrity`
 
 Creates an `Integrity` object from either string or `Buffer` data, calculating

index.js

@@ -29,6 +29,13 @@ class IntegrityMetadata {
     const rawOpts = match[3]
     this.options = rawOpts ? rawOpts.slice(1).split('?') : []
   }
+  hexDigest () {
+    return this.digest && (
+      Buffer.from
+      ? Buffer.from(this.digest, 'base64')
+      : new Buffer(this.digest, 'base64')
+    ).toString('hex')
+  }
   toString (opts) {
     if (opts && opts.strict) {
       // Strict mode enforces the standard as close to the foot of the

test/integrity.js

@@ -81,6 +81,17 @@ test('pickAlgorithm()', t => {
   t.done()
 })
 
+test('IntegrityMetadata.hexDigest()', t => {
+  const sri = ssri.parse('sha512-bar', {single: true})
+  t.equal(
+    sri.hexDigest(),
+    (
+      Buffer.from ? Buffer.from('bar', 'base64') : new Buffer('bar', 'base64')
+    ).toString('hex'),
+    'returned hex version of base64 digest')
+  t.done()
+})
+
 test('semi-private', t => {
   t.equal(ssri.Integrity, undefined, 'Integrity class is module-private.')
   t.done()