1 files changed, 114 insertions, 0 deletions
diff --git a/modules/git/object_id.go b/modules/git/object_id.go
new file mode 100644
index 00000000..ecbc1587
--- /dev/null
+++ b/modules/git/object_id.go
@@ -0,0 +1,114 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"bytes"
+	"encoding/hex"
+	"fmt"
+)
+
+type ObjectID interface {
+	String() string
+	IsZero() bool
+	RawValue() []byte
+	Type() ObjectFormat
+}
+
+/* SHA1 */
+type Sha1Hash [20]byte
+
+func (h *Sha1Hash) String() string {
+	return hex.EncodeToString(h[:])
+}
+
+func (h *Sha1Hash) IsZero() bool {
+	empty := Sha1Hash{}
+	return bytes.Equal(empty[:], h[:])
+}
+func (h *Sha1Hash) RawValue() []byte { return h[:] }
+func (*Sha1Hash) Type() ObjectFormat { return Sha1ObjectFormat }
+
+var _ ObjectID = &Sha1Hash{}
+
+func MustIDFromString(hexHash string) ObjectID {
+	id, err := NewIDFromString(hexHash)
+	if err != nil {
+		panic(err)
+	}
+	return id
+}
+
+/* SHA256 */
+type Sha256Hash [32]byte
+
+func (h *Sha256Hash) String() string {
+	return hex.EncodeToString(h[:])
+}
+
+func (h *Sha256Hash) IsZero() bool {
+	empty := Sha256Hash{}
+	return bytes.Equal(empty[:], h[:])
+}
+func (h *Sha256Hash) RawValue() []byte { return h[:] }
+func (*Sha256Hash) Type() ObjectFormat { return Sha256ObjectFormat }
+
+/* utility */
+func NewIDFromString(hexHash string) (ObjectID, error) {
+	var theObjectFormat ObjectFormat
+	for _, objectFormat := range SupportedObjectFormats {
+		if len(hexHash) == objectFormat.FullLength() {
+			theObjectFormat = objectFormat
+			break
+		}
+	}
+
+	if theObjectFormat == nil {
+		return nil, fmt.Errorf("length %d has no matched object format: %s", len(hexHash), hexHash)
+	}
+
+	b, err := hex.DecodeString(hexHash)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(b) != theObjectFormat.FullLength()/2 {
+		return theObjectFormat.EmptyObjectID(), fmt.Errorf("length must be %d: %v", theObjectFormat.FullLength(), b)
+	}
+	return theObjectFormat.MustID(b), nil
+}
+
+// IsEmptyCommitID checks if an hexadecimal string represents an empty commit according to git (only '0').
+// If objectFormat is not nil, the length will be checked as well (otherwise the length must match the sha1 or sha256 length).
+func IsEmptyCommitID(commitID string, objectFormat ObjectFormat) bool {
+	if commitID == "" {
+		return true
+	}
+	if objectFormat == nil {
+		if Sha1ObjectFormat.FullLength() != len(commitID) && Sha256ObjectFormat.FullLength() != len(commitID) {
+			return false
+		}
+	} else if objectFormat.FullLength() != len(commitID) {
+		return false
+	}
+	for _, c := range commitID {
+		if c != '0' {
+			return false
+		}
+	}
+	return true
+}
+
+// ComputeBlobHash compute the hash for a given blob content
+func ComputeBlobHash(hashType ObjectFormat, content []byte) ObjectID {
+	return hashType.ComputeHash(ObjectBlob, content)
+}
+
+type ErrInvalidSHA struct {
+	SHA string
+}
+
+func (err ErrInvalidSHA) Error() string {
+	return fmt.Sprintf("invalid sha: %s", err.SHA)
+}