crypto: add Hash.prototype.copy() method

doc/api/crypto.md

@@ -1041,6 +1041,43 @@ console.log(hash.digest('hex'));
 //   6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
 ```
 
+### hash.copy(\[options\])
+<!-- YAML
+added:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/29910
+-->
+
+* `options` {Object} [`stream.transform` options][]
+* Returns: {Hash}
+
+Creates a new `Hash` object that contains a deep copy of the internal state
+of the current `Hash` object.
+
+The optional `options` argument controls stream behavior. For XOF hash
+functions such as `'shake256'`, the `outputLength` option can be used to
+specify the desired output length in bytes.
+
+An error is thrown when an attempt is made to copy the `Hash` object after
+its [`hash.digest()`][] method has been called.
+
+```js
+// Calculate a rolling hash.
+const crypto = require('crypto');
+const hash = crypto.createHash('sha256');
+
+hash.update('one');
+console.log(hash.copy().digest('hex'));
+
+hash.update('two');
+console.log(hash.copy().digest('hex'));
+
+hash.update('three');
+console.log(hash.copy().digest('hex'));
+
+// Etc.
+```
+
 ### hash.digest(\[encoding\])
 <!-- YAML
 added: v0.1.92

lib/internal/crypto/hash.js

@@ -34,7 +34,8 @@ const kFinalized = Symbol('kFinalized');
 function Hash(algorithm, options) {
   if (!(this instanceof Hash))
     return new Hash(algorithm, options);
-  validateString(algorithm, 'algorithm');
+  if (!(algorithm instanceof _Hash))
+    validateString(algorithm, 'algorithm');
   const xofLen = typeof options === 'object' && options !== null ?
     options.outputLength : undefined;
   if (xofLen !== undefined)
@@ -49,6 +50,14 @@ function Hash(algorithm, options) {
 Object.setPrototypeOf(Hash.prototype, LazyTransform.prototype);
 Object.setPrototypeOf(Hash, LazyTransform);
 
+Hash.prototype.copy = function copy(options) {
+  const state = this[kState];
+  if (state[kFinalized])
+    throw new ERR_CRYPTO_HASH_FINALIZED();
+
+  return new Hash(this[kHandle], options);
+};
+
 Hash.prototype._transform = function _transform(chunk, encoding, callback) {
   this[kHandle].update(chunk, encoding);
   callback();

src/node_crypto.cc

@@ -4720,7 +4720,16 @@ void Hash::Initialize(Environment* env, Local<Object> target) {
 void Hash::New(const FunctionCallbackInfo<Value>& args) {
   Environment* env = Environment::GetCurrent(args);
 
-  const node::Utf8Value hash_type(env->isolate(), args[0]);
+  const Hash* orig = nullptr;
+  const EVP_MD* md = nullptr;
+
+  if (args[0]->IsObject()) {
+    ASSIGN_OR_RETURN_UNWRAP(&orig, args[0].As<Object>());
+    md = EVP_MD_CTX_md(orig->mdctx_.get());
+  } else {
+    const node::Utf8Value hash_type(env->isolate(), args[0]);
+    md = EVP_get_digestbyname(*hash_type);
+  }
 
   Maybe<unsigned int> xof_md_len = Nothing<unsigned int>();
   if (!args[1]->IsUndefined()) {
@@ -4729,17 +4738,19 @@ void Hash::New(const FunctionCallbackInfo<Value>& args) {
   }
 
   Hash* hash = new Hash(env, args.This());
-  if (!hash->HashInit(*hash_type, xof_md_len)) {
+  if (md == nullptr || !hash->HashInit(md, xof_md_len)) {
     return ThrowCryptoError(env, ERR_get_error(),
                             "Digest method not supported");
   }
+
+  if (orig != nullptr &&
+      0 >= EVP_MD_CTX_copy(hash->mdctx_.get(), orig->mdctx_.get())) {
+    return ThrowCryptoError(env, ERR_get_error(), "Digest copy error");
+  }
 }
 
 
-bool Hash::HashInit(const char* hash_type, Maybe<unsigned int> xof_md_len) {
-  const EVP_MD* md = EVP_get_digestbyname(hash_type);
-  if (md == nullptr)
-    return false;
+bool Hash::HashInit(const EVP_MD* md, Maybe<unsigned int> xof_md_len) {
   mdctx_.reset(EVP_MD_CTX_new());
   if (!mdctx_ || EVP_DigestInit_ex(mdctx_.get(), md, nullptr) <= 0) {
     mdctx_.reset();

src/node_crypto.h

@@ -591,7 +591,7 @@ class Hash : public BaseObject {
   SET_MEMORY_INFO_NAME(Hash)
   SET_SELF_SIZE(Hash)
 
-  bool HashInit(const char* hash_type, v8::Maybe<unsigned int> xof_md_len);
+  bool HashInit(const EVP_MD* md, v8::Maybe<unsigned int> xof_md_len);
   bool HashUpdate(const char* data, int len);
 
  protected:

test/parallel/test-crypto-hash.js

@@ -192,14 +192,27 @@ common.expectsError(
   assert.strictEqual(crypto.createHash('shake256').digest('hex'),
                      '46b9dd2b0ba88d13233b3feb743eeb24' +
                      '3fcd52ea62b81b82b50c27646ed5762f');
+  assert.strictEqual(crypto.createHash('shake256', { outputLength: 0 })
+                           .copy()  // Default outputLength.
+                           .digest('hex'),
+                     '46b9dd2b0ba88d13233b3feb743eeb24' +
+                     '3fcd52ea62b81b82b50c27646ed5762f');
 
   // Short outputLengths.
   assert.strictEqual(crypto.createHash('shake128', { outputLength: 0 })
                            .digest('hex'),
                      '');
+  assert.strictEqual(crypto.createHash('shake128', { outputLength: 5 })
+                           .copy({ outputLength: 0 })
+                           .digest('hex'),
+                     '');
   assert.strictEqual(crypto.createHash('shake128', { outputLength: 5 })
                            .digest('hex'),
                      '7f9c2ba4e8');
+  assert.strictEqual(crypto.createHash('shake128', { outputLength: 0 })
+                           .copy({ outputLength: 5 })
+                           .digest('hex'),
+                     '7f9c2ba4e8');
   assert.strictEqual(crypto.createHash('shake128', { outputLength: 15 })
                            .digest('hex'),
                      '7f9c2ba4e88f827d61604550760585');
@@ -249,3 +262,19 @@ common.expectsError(
                         { code: 'ERR_OUT_OF_RANGE' });
   }
 }
+
+{
+  const h = crypto.createHash('sha512');
+  h.digest();
+  common.expectsError(() => h.copy(), { code: 'ERR_CRYPTO_HASH_FINALIZED' });
+  common.expectsError(() => h.digest(), { code: 'ERR_CRYPTO_HASH_FINALIZED' });
+}
+
+{
+  const a = crypto.createHash('sha512').update('abc');
+  const b = a.copy();
+  const c = b.copy().update('def');
+  const d = crypto.createHash('sha512').update('abcdef');
+  assert.strictEqual(a.digest('hex'), b.digest('hex'));
+  assert.strictEqual(c.digest('hex'), d.digest('hex'));
+}