crypto: return `this` in setAuthTag/setAAD

Allow method chaining as with setAutoPadding and other methods.

PR-URL: https://github.com/nodejs/node/pull/9398
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Sam Roberts <sam@strongloop.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/crypto.md

@@ -194,6 +194,8 @@ When using an authenticated encryption mode (only `GCM` is currently
 supported), the `cipher.setAAD()` method sets the value used for the
 _additional authenticated data_ (AAD) input parameter.
 
+Returns `this` for method chaining.
+
 ### cipher.getAuthTag()
 <!-- YAML
 added: v1.0.0
@@ -222,6 +224,8 @@ using `0x0` instead of PKCS padding.
 
 The `cipher.setAutoPadding()` method must be called before [`cipher.final()`][].
 
+Returns `this` for method chaining.
+
 ### cipher.update(data[, input_encoding][, output_encoding])
 <!-- YAML
 added: v0.1.94
@@ -329,6 +333,8 @@ When using an authenticated encryption mode (only `GCM` is currently
 supported), the `decipher.setAAD()` method sets the value used for the
 _additional authenticated data_ (AAD) input parameter.
 
+Returns `this` for method chaining.
+
 ### decipher.setAuthTag(buffer)
 <!-- YAML
 added: v1.0.0
@@ -340,6 +346,8 @@ received _authentication tag_. If no tag is provided, or if the cipher text
 has been tampered with, [`decipher.final()`][] with throw, indicating that the
 cipher text should be discarded due to failed authentication.
 
+Returns `this` for method chaining.
+
 ### decipher.setAutoPadding(auto_padding=true)
 <!-- YAML
 added: v0.7.1
@@ -355,6 +363,8 @@ multiple of the ciphers block size.
 The `decipher.setAutoPadding()` method must be called before
 [`decipher.update()`][].
 
+Returns `this` for method chaining.
+
 ### decipher.update(data[, input_encoding][, output_encoding])
 <!-- YAML
 added: v0.1.94

lib/crypto.js

@@ -178,10 +178,12 @@ Cipher.prototype.getAuthTag = function() {
 
 Cipher.prototype.setAuthTag = function(tagbuf) {
   this._handle.setAuthTag(tagbuf);
+  return this;
 };
 
 Cipher.prototype.setAAD = function(aadbuf) {
   this._handle.setAAD(aadbuf);
+  return this;
 };
 
 exports.createCipheriv = exports.Cipheriv = Cipheriv;

test/parallel/test-crypto-cipher-decipher.js

@@ -139,3 +139,14 @@ testCipher2(Buffer.from('0123456789abcdef'));
   assert.doesNotThrow(() => txt += decipher.final('utf-16le'));
   assert.strictEqual(txt, plaintext, 'decrypted result in utf-16le');
 }
+
+// setAutoPadding/setAuthTag/setAAD should return `this`
+{
+  const key = '0123456789';
+  const tagbuf = Buffer.from('tagbuf');
+  const aadbuf = Buffer.from('aadbuf');
+  const decipher = crypto.createDecipher('aes-256-gcm', key);
+  assert.strictEqual(decipher.setAutoPadding(), decipher);
+  assert.strictEqual(decipher.setAuthTag(tagbuf), decipher);
+  assert.strictEqual(decipher.setAAD(aadbuf), decipher);
+}