feat: adding ssri.create for a crypto style interface (#2)

* feat: adding ssri.create for a crypto style interface

adding crypto.create
adding toJSON to Integrity

* chore: standard

* fix: update nits and fix documentation for create.

create was misdocumented as returning Integrity but it return a Hash

README.md

@@ -20,12 +20,14 @@ Integrity](https://w3c.github.io/webappsec/specs/subresourceintegrity/) hashes.
     * [`stringify`](#stringify)
     * [`Integrity#concat`](#integrity-concat)
     * [`Integrity#toString`](#integrity-to-string)
+    * [`Integrity#toJSON`](#integrity-to-json)
     * [`Integrity#pickAlgorithm`](#integrity-pick-algorithm)
     * [`Integrity#hexDigest`](#integrity-hex-digest)
   * Integrity Generation
     * [`fromHex`](#from-hex)
     * [`fromData`](#from-data)
     * [`fromStream`](#from-stream)
+    * [`create`](#create)
   * Integrity Verification
     * [`checkData`](#check-data)
     * [`checkStream`](#check-stream)
@@ -200,6 +202,22 @@ const integrity = 'sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xp
 ssri.parse(integrity).toString() === integrity
 ```
 
+#### <a name="integrity-to-json"></a> `> Integrity#toJSON() -> String`
+
+Returns the string representation of an `Integrity` object. All hash entries
+will be concatenated in the string by `' '`.
+
+This is a convenience method so you can pass an `Integrity` object directly to `JSON.stringify`.
+For more info check out [toJSON() behavior on mdn](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify#toJSON%28%29_behavior).
+
+##### Example
+
+```javascript
+const integrity = '"sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==?foo"'
+
+JSON.stringify(ssri.parse(integrity)) === integrity
+```
+
 #### <a name="integrity-pick-algorithm"></a> `> Integrity#pickAlgorithm([opts]) -> String`
 
 Returns the "best" algorithm from those available in the integrity object.
@@ -312,6 +330,30 @@ ssri.fromStream(fs.createReadStream('index.js'), {
 }) // succeeds
 ```
 
+#### <a name="create"></a> `> ssri.create([opts]) -> <Hash>`
+
+Returns a Hash object with `update(<Buffer or string>[,enc])` and `digest()` methods.
+
+
+The Hash object provides the same methods as [crypto class Hash](https://nodejs.org/dist/latest-v6.x/docs/api/crypto.html#crypto_class_hash).
+`digest()` accepts no arguments and returns an Integrity object calculated by reading data from
+calls to update.
+
+It accepts both `opts.algorithms` and `opts.options`, which are documented as
+part of [`ssri.fromData`](#from-data).
+
+If `opts.strict` is true, the integrity object will be created using strict
+parsing rules. See [`ssri.parse`](#parse).
+
+##### Example
+
+```javascript
+const integrity = ssri.create().update('foobarbaz').digest()
+integrity.toString()
+// ->
+// sha512-yzd8ELD1piyANiWnmdnpCL5F52f10UfUdEkHywVZeqTt0ymgrxR63Qz0GB7TKPoeeZQmWCaz7T1+9vBnypkYWg==
+```
+
 #### <a name="check-data"></a> `> ssri.checkData(data, sri, [opts]) -> Hash|false`
 
 Verifies `data` integrity against an `sri` argument. `data` may be either a

index.js

@@ -33,6 +33,9 @@ class Hash {
   hexDigest () {
     return this.digest && bufFrom(this.digest, 'base64').toString('hex')
   }
+  toJSON () {
+    return this.toString()
+  }
   toString (opts) {
     if (opts && opts.strict) {
       // Strict mode enforces the standard as close to the foot of the
@@ -63,6 +66,9 @@ class Hash {
 
 class Integrity {
   get isIntegrity () { return true }
+  toJSON () {
+    return this.toString()
+  }
   toString (opts) {
     opts = opts || {}
     let sep = opts.sep || ' '
@@ -275,6 +281,41 @@ function integrityStream (opts) {
   return stream
 }
 
+module.exports.create = createIntegrity
+function createIntegrity (opts) {
+  opts = opts || {}
+  const algorithms = opts.algorithms || ['sha512']
+  const optString = opts.options && opts.options.length
+  ? `?${opts.options.join('?')}`
+  : ''
+
+  const hashes = algorithms.map(crypto.createHash)
+
+  return {
+    update: function (chunk, enc) {
+      hashes.forEach(h => h.update(chunk, enc))
+      return this
+    },
+    digest: function (enc) {
+      const integrity = algorithms.reduce((acc, algo) => {
+        const digest = hashes.shift().digest('base64')
+        const hash = new Hash(
+          `${algo}-${digest}${optString}`,
+           opts
+        )
+        if (hash.algorithm && hash.digest) {
+          const algo = hash.algorithm
+          if (!acc[algo]) { acc[algo] = [] }
+          acc[algo].push(hash)
+        }
+        return acc
+      }, new Integrity())
+
+      return integrity
+    }
+  }
+}
+
 // This is a Best Effort™ at a reasonable priority for hash algos
 const DEFAULT_PRIORITY = [
   'md5', 'whirlpool', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512'

test/create.js

@@ -0,0 +1,24 @@
+const test = require('tap').test
+
+const ssri = require('..')
+
+test('works just like from', function (t) {
+  const integrity = ssri.fromData('hi')
+  const integrityCreate = ssri.create().update('hi').digest()
+
+  t.ok(integrityCreate instanceof integrity.constructor, 'should be same Integrity that fromData returns')
+  t.equals(integrity + '', integrityCreate + '', 'should be the sam as fromData')
+  t.end()
+})
+
+test('can pass options', function (t) {
+  const integrity = ssri.create({algorithms: ['sha256', 'sha384']}).update('hi').digest()
+
+  t.equals(
+    integrity + '',
+    'sha256-j0NDRmSPa5bfid2pAcUXaxCm2Dlh3TwayItZstwyeqQ= ' +
+    'sha384-B5EAbfgShHckT1PQ/c4hDbgfVXV1EOJqzuNcGKa86qKNzbv9bcBBubTcextU439S',
+    'should be expected value'
+  )
+  t.end()
+})

test/integrity.js

@@ -24,6 +24,21 @@ test('toString()', t => {
   t.done()
 })
 
+test('toJSON()', t => {
+  const sri = ssri.parse('sha512-foo sha256-bar!')
+  t.equal(
+    sri.toJSON(),
+    'sha512-foo sha256-bar!',
+    'integrity objects from ssri.parse() can use toJSON()'
+  )
+  t.equal(
+    sri.sha512[0].toJSON(),
+    'sha512-foo',
+    'hash objects should toJSON also'
+  )
+  t.done()
+})
+
 test('concat()', t => {
   const sri = ssri.parse('sha512-foo')
   t.equal(