crypto: do not overwrite _writableState.defaultEncoding

This only affects the writable side of LazyTransform and should not
change the behavior of any LazyTransform streams (Cipher, Decipher,
Cipheriv, Decipheriv, Hash, Hmac).

If the user does not set defaultEncoding when creating a transform
stream, WritableState uses 'utf8' by default. Only LazyTransform
overwrites this with 'buffer' for strict backward compatibility. This
was necessary when crypto.DEFAULT_ENCODING still existed. Now that
DEFAULT_ENCODING has been removed, defaultEncoding is always 'buffer'.
The writable side of LazyTransform appears to treat 'utf8' and 'buffer'
in exactly the same way. Therefore, there seems to be no need to
overwrite _writableState.defaultEncoding at this point.

Nevertheless, because Node.js has failed to hide implementation details
such as _writableState from the ecosystem, we may want to consider this
a breaking change.

Refs: nodejs#47182
Refs: nodejs#8611
PR-URL: nodejs#49140
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: tniessen

lib/internal/streams/lazy_transform.js

@@ -23,11 +23,6 @@ function makeGetter(name) {
   return function() {
     stream.Transform.call(this, this._options);
     this._writableState.decodeStrings = false;
-
-    if (!this._options || !this._options.defaultEncoding) {
-      this._writableState.defaultEncoding = 'buffer';  // TODO(tniessen): remove
-    }
-
     return this[name];
   };
 }

test/parallel/test-crypto.js

@@ -298,6 +298,9 @@ function testEncoding(options, assertionHash) {
   let hashValue = '';
 
   hash.on('data', (data) => {
+    // The defaultEncoding has no effect on the hash value. It only affects data
+    // consumed by the Hash transform stream.
+    assert(Buffer.isBuffer(data));
     hashValue += data.toString('hex');
   });
 
@@ -307,6 +310,8 @@ function testEncoding(options, assertionHash) {
 
   hash.write('öäü');
   hash.end();
+
+  assert.strictEqual(hash._writableState.defaultEncoding, options?.defaultEncoding ?? 'utf8');
 }
 
 // Hash of "öäü" in utf8 format