Implement Clone for all hashers (#167)

* implement Clone for all hashers

* document clone methods

* add TestHash_Clone comment

Author: qmuntal

hash.go

@@ -230,6 +230,34 @@ func (h *evpHash) sum(out []byte) {
 	runtime.KeepAlive(h)
 }
 
+// clone returns a new evpHash object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *evpHash) clone() (*evpHash, error) {
+	ctx := C.go_openssl_EVP_MD_CTX_new()
+	if ctx == nil {
+		return nil, newOpenSSLError("EVP_MD_CTX_new")
+	}
+	if C.go_openssl_EVP_MD_CTX_copy_ex(ctx, h.ctx) != 1 {
+		C.go_openssl_EVP_MD_CTX_free(ctx)
+		return nil, newOpenSSLError("EVP_MD_CTX_copy")
+	}
+	ctx2 := C.go_openssl_EVP_MD_CTX_new()
+	if ctx2 == nil {
+		C.go_openssl_EVP_MD_CTX_free(ctx)
+		return nil, newOpenSSLError("EVP_MD_CTX_new")
+	}
+	cloned := &evpHash{
+		ctx:          ctx,
+		ctx2:         ctx2,
+		size:         h.size,
+		blockSize:    h.blockSize,
+		marshallable: h.marshallable,
+	}
+	runtime.SetFinalizer(cloned, (*evpHash).finalize)
+	return cloned, nil
+}
+
 // hashState returns a pointer to the internal hash structure.
 //
 // The EVP_MD_CTX memory layout has changed in OpenSSL 3
@@ -280,6 +308,17 @@ func (h *md4Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *md4Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &md4Hash{evpHash: c}, nil
+}
+
 // NewMD5 returns a new MD5 hash.
 func NewMD5() hash.Hash {
 	h := md5Hash{evpHash: newEvpHash(crypto.MD5)}
@@ -308,6 +347,17 @@ func (h *md5Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *md5Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &md5Hash{evpHash: c}, nil
+}
+
 const (
 	md5Magic         = "md5\x01"
 	md5MarshaledSize = len(md5Magic) + 4*4 + 64 + 8
@@ -377,6 +427,17 @@ func (h *sha1Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha1Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha1Hash{evpHash: c}, nil
+}
+
 // sha1State layout is taken from
 // https://github.com/openssl/openssl/blob/0418e993c717a6863f206feaa40673a261de7395/include/openssl/sha.h#L34.
 type sha1State struct {
@@ -457,6 +518,17 @@ func (h *sha224Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha224Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha224Hash{evpHash: c}, nil
+}
+
 // NewSHA256 returns a new SHA256 hash.
 func NewSHA256() hash.Hash {
 	h := sha256Hash{evpHash: newEvpHash(crypto.SHA256)}
@@ -476,6 +548,17 @@ func (h *sha256Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha256Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha256Hash{evpHash: c}, nil
+}
+
 const (
 	magic224         = "sha\x02"
 	magic256         = "sha\x03"
@@ -616,6 +699,17 @@ func (h *sha384Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha384Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha384Hash{evpHash: c}, nil
+}
+
 // NewSHA512 returns a new SHA512 hash.
 func NewSHA512() hash.Hash {
 	h := sha512Hash{evpHash: newEvpHash(crypto.SHA512)}
@@ -635,6 +729,17 @@ func (h *sha512Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha512Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha512Hash{evpHash: c}, nil
+}
+
 // sha512State layout is taken from
 // https://github.com/openssl/openssl/blob/0418e993c717a6863f206feaa40673a261de7395/include/openssl/sha.h#L95.
 type sha512State struct {
@@ -781,6 +886,17 @@ func (h *sha3_224Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha3_224Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha3_224Hash{evpHash: c}, nil
+}
+
 // NewSHA3_256 returns a new SHA3-256 hash.
 func NewSHA3_256() hash.Hash {
 	return &sha3_256Hash{
@@ -798,6 +914,17 @@ func (h *sha3_256Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha3_256Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha3_256Hash{evpHash: c}, nil
+}
+
 // NewSHA3_384 returns a new SHA3-384 hash.
 func NewSHA3_384() hash.Hash {
 	return &sha3_384Hash{
@@ -815,6 +942,17 @@ func (h *sha3_384Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha3_384Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha3_384Hash{evpHash: c}, nil
+}
+
 // NewSHA3_512 returns a new SHA3-512 hash.
 func NewSHA3_512() hash.Hash {
 	return &sha3_512Hash{
@@ -832,6 +970,17 @@ func (h *sha3_512Hash) Sum(in []byte) []byte {
 	return append(in, h.out[:]...)
 }
 
+// Clone returns a new [hash.Hash] object that is a deep clone of itself.
+// The duplicate object contains all state and data contained in the
+// original object at the point of duplication.
+func (h *sha3_512Hash) Clone() (hash.Hash, error) {
+	c, err := h.clone()
+	if err != nil {
+		return nil, err
+	}
+	return &sha3_512Hash{evpHash: c}, nil
+}
+
 // appendUint64 appends x into b as a big endian byte sequence.
 func appendUint64(b []byte, x uint64) []byte {
 	return append(b,