Add hash.Clone interface for HMAC and Hash (#283)

* fix: add clone method for openssl hmac and hash

* fix:panic error returns

* fix:remove unrelated comment

* fix:remove unrelated comment

* fix: bring back the free functions

* fix: bring back the free functions

Author: mertakman

hash.go

@@ -223,18 +223,8 @@ func NewSHA3_512() hash.Hash {
 	return newEvpHash(crypto.SHA3_512)
 }
 
-// cloneHash is an interface that defines a Clone method.
-//
-// hahs.CloneHash will probably be added in Go 1.25, see https://golang.org/issue/69521,
-// but we need it now.
-type cloneHash interface {
-	hash.Hash
-	// Clone returns a separate Hash instance with the same state as h.
-	Clone() hash.Hash
-}
-
 var _ hash.Hash = (*evpHash)(nil)
-var _ cloneHash = (*evpHash)(nil)
+var _ HashCloner = (*evpHash)(nil)
 
 // evpHash implements generic hash methods.
 type evpHash struct {
@@ -359,7 +349,7 @@ func (h *evpHash) Sum(in []byte) []byte {
 // 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() hash.Hash {
+func (h *evpHash) Clone() (HashCloner, error) {
 	h2 := &evpHash{alg: h.alg}
 	if h.ctx != nil {
 		var err error
@@ -379,7 +369,7 @@ func (h *evpHash) Clone() hash.Hash {
 		runtime.SetFinalizer(h2, (*evpHash).finalize)
 	}
 	runtime.KeepAlive(h)
-	return h2
+	return h2, nil
 }
 
 var errHashNotMarshallable = errors.New("openssl: hash state is not marshallable")

hash_test.go

@@ -232,21 +232,42 @@ func TestHash_Clone(t *testing.T) {
 			if !openssl.SupportsHash(ch) {
 				t.Skip("not supported")
 			}
-			h := cryptoToHash(ch)()
-			if _, ok := h.(encoding.BinaryMarshaler); !ok {
-				t.Skip("not supported")
-			}
+			h := cryptoToHash(ch)().(openssl.HashCloner)
 			_, err := h.Write(msg)
 			if err != nil {
 				t.Fatal(err)
 			}
-			// We don't define an interface for the Clone method to avoid other
-			// packages from depending on it. Use type assertion to call it.
-			h2 := h.(interface{ Clone() hash.Hash }).Clone()
-			h.Write(msg)
-			h2.Write(msg)
-			if actual, actual2 := h.Sum(nil), h2.Sum(nil); !bytes.Equal(actual, actual2) {
-				t.Errorf("%s(%q) = 0x%x != cloned 0x%x", ch.String(), msg, actual, actual2)
+
+			h3, err := h.Clone()
+			if err != nil {
+				t.Fatalf("Clone failed: %v", err)
+			}
+			prefix := []byte("tmp")
+			writeToHash(t, h, prefix)
+			h2, err := h.Clone()
+			if err != nil {
+				t.Fatalf("Clone failed: %v", err)
+			}
+			prefixSum := h.Sum(nil)
+			if !bytes.Equal(prefixSum, h2.Sum(nil)) {
+				t.Fatalf("%T Clone results are inconsistent", h)
+			}
+			suffix := []byte("tmp2")
+			writeToHash(t, h, suffix)
+			writeToHash(t, h3, append(prefix, suffix...))
+			compositeSum := h3.Sum(nil)
+			if !bytes.Equal(h.Sum(nil), compositeSum) {
+				t.Fatalf("%T Clone results are inconsistent", h)
+			}
+			if !bytes.Equal(h2.Sum(nil), prefixSum) {
+				t.Fatalf("%T Clone results are inconsistent", h)
+			}
+			writeToHash(t, h2, suffix)
+			if !bytes.Equal(h.Sum(nil), compositeSum) {
+				t.Fatalf("%T Clone results are inconsistent", h)
+			}
+			if !bytes.Equal(h2.Sum(nil), compositeSum) {
+				t.Fatalf("%T Clone results are inconsistent", h)
 			}
 		})
 	}
@@ -519,3 +540,20 @@ func (h *stubHash) Sum(in []byte) []byte        { return in }
 func (h *stubHash) Reset()                      {}
 func (h *stubHash) Size() int                   { return 0 }
 func (h *stubHash) BlockSize() int              { return 0 }
+
+// Helper function for writing. Verifies that Write does not error.
+func writeToHash(t *testing.T, h hash.Hash, p []byte) {
+	t.Helper()
+
+	before := make([]byte, len(p))
+	copy(before, p)
+
+	n, err := h.Write(p)
+	if err != nil || n != len(p) {
+		t.Errorf("Write returned error; got (%v, %v), want (nil, %v)", err, n, len(p))
+	}
+
+	if !bytes.Equal(p, before) {
+		t.Errorf("Write modified input slice; got %x, want %x", p, before)
+	}
+}

hashclone.go

@@ -0,0 +1,14 @@
+//go:build !cmd_go_bootstrap
+
+package openssl
+
+import (
+	"hash"
+)
+
+// HashCloner is an interface that defines a Clone method.
+type HashCloner interface {
+	hash.Hash
+	// Clone returns a separate Hash instance with the same state as h.
+	Clone() (HashCloner, error)
+}

hashclone_go125.go

@@ -0,0 +1,9 @@
+//go:build go1.25 && !cmd_go_bootstrap
+
+package openssl
+
+import (
+	"hash"
+)
+
+type HashCloner = hash.Cloner

hmac.go

@@ -6,6 +6,7 @@ import "C"
 import (
 	"hash"
 	"runtime"
+	"slices"
 	"sync"
 	"unsafe"
 
@@ -242,3 +243,41 @@ func (h *opensslHMAC) Sum(in []byte) []byte {
 	}
 	return append(in, h.sum[:h.size]...)
 }
+
+func (h *opensslHMAC) Clone() (HashCloner, error) {
+	switch vMajor {
+	case 1:
+		ctx2, err := ossl.HMAC_CTX_new()
+		if err != nil {
+			panic(err)
+		}
+		if _, err := ossl.HMAC_CTX_copy(ctx2, h.ctx1.ctx); err != nil {
+			ossl.HMAC_CTX_free(ctx2)
+			panic(err)
+		}
+		cl := &opensslHMAC{
+			ctx1:      hmacCtx1{ctx: ctx2},
+			size:      h.size,
+			blockSize: h.blockSize,
+		}
+		runtime.SetFinalizer(cl, (*opensslHMAC).finalize)
+		return cl, nil
+
+	case 3:
+		ctx2, err := ossl.EVP_MAC_CTX_dup(h.ctx3.ctx)
+		if err != nil {
+			panic(err)
+		}
+
+		cl := &opensslHMAC{
+			ctx3:      hmacCtx3{ctx: ctx2, key: slices.Clone(h.ctx3.key)},
+			size:      h.size,
+			blockSize: h.blockSize,
+		}
+		runtime.SetFinalizer(cl, (*opensslHMAC).finalize)
+		return cl, nil
+
+	default:
+		panic(errUnsupportedVersion())
+	}
+}