1 files changed, 143 insertions, 0 deletions
diff --git a/modules/git/object_format.go b/modules/git/object_format.go
new file mode 100644
index 0000000..db9120d
--- /dev/null
+++ b/modules/git/object_format.go
@@ -0,0 +1,143 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package git
+
+import (
+	"crypto/sha1"
+	"crypto/sha256"
+	"hash"
+	"regexp"
+	"strconv"
+)
+
+// sha1Pattern can be used to determine if a string is an valid sha
+var sha1Pattern = regexp.MustCompile(`^[0-9a-f]{4,40}$`)
+
+// sha256Pattern can be used to determine if a string is an valid sha
+var sha256Pattern = regexp.MustCompile(`^[0-9a-f]{4,64}$`)
+
+type ObjectFormat interface {
+	// Name returns the name of the object format
+	Name() string
+	// EmptyObjectID creates a new empty ObjectID from an object format hash name
+	EmptyObjectID() ObjectID
+	// EmptyTree is the hash of an empty tree
+	EmptyTree() ObjectID
+	// FullLength is the length of the hash's hex string
+	FullLength() int
+	// IsValid returns true if the input is a valid hash
+	IsValid(input string) bool
+	// MustID creates a new ObjectID from a byte slice
+	MustID(b []byte) ObjectID
+	// ComputeHash compute the hash for a given ObjectType and content
+	ComputeHash(t ObjectType, content []byte) ObjectID
+}
+
+func computeHash(dst []byte, hasher hash.Hash, t ObjectType, content []byte) {
+	_, _ = hasher.Write(t.Bytes())
+	_, _ = hasher.Write([]byte(" "))
+	_, _ = hasher.Write([]byte(strconv.Itoa(len(content))))
+	_, _ = hasher.Write([]byte{0})
+	_, _ = hasher.Write(content)
+	hasher.Sum(dst)
+}
+
+/* SHA1 Type */
+type Sha1ObjectFormatImpl struct{}
+
+var (
+	emptySha1ObjectID = &Sha1Hash{}
+	emptySha1Tree     = &Sha1Hash{
+		0x4b, 0x82, 0x5d, 0xc6, 0x42, 0xcb, 0x6e, 0xb9, 0xa0, 0x60,
+		0xe5, 0x4b, 0xf8, 0xd6, 0x92, 0x88, 0xfb, 0xee, 0x49, 0x04,
+	}
+)
+
+func (Sha1ObjectFormatImpl) Name() string { return "sha1" }
+func (Sha1ObjectFormatImpl) EmptyObjectID() ObjectID {
+	return emptySha1ObjectID
+}
+
+func (Sha1ObjectFormatImpl) EmptyTree() ObjectID {
+	return emptySha1Tree
+}
+func (Sha1ObjectFormatImpl) FullLength() int { return 40 }
+func (Sha1ObjectFormatImpl) IsValid(input string) bool {
+	return sha1Pattern.MatchString(input)
+}
+
+func (Sha1ObjectFormatImpl) MustID(b []byte) ObjectID {
+	var id Sha1Hash
+	copy(id[0:20], b)
+	return &id
+}
+
+// ComputeHash compute the hash for a given ObjectType and content
+func (h Sha1ObjectFormatImpl) ComputeHash(t ObjectType, content []byte) ObjectID {
+	var obj Sha1Hash
+	computeHash(obj[:0], sha1.New(), t, content)
+	return &obj
+}
+
+/* SHA256 Type */
+type Sha256ObjectFormatImpl struct{}
+
+var (
+	emptySha256ObjectID = &Sha256Hash{}
+	emptySha256Tree     = &Sha256Hash{
+		0x6e, 0xf1, 0x9b, 0x41, 0x22, 0x5c, 0x53, 0x69, 0xf1, 0xc1,
+		0x04, 0xd4, 0x5d, 0x8d, 0x85, 0xef, 0xa9, 0xb0, 0x57, 0xb5,
+		0x3b, 0x14, 0xb4, 0xb9, 0xb9, 0x39, 0xdd, 0x74, 0xde, 0xcc,
+		0x53, 0x21,
+	}
+)
+
+func (Sha256ObjectFormatImpl) Name() string { return "sha256" }
+func (Sha256ObjectFormatImpl) EmptyObjectID() ObjectID {
+	return emptySha256ObjectID
+}
+
+func (Sha256ObjectFormatImpl) EmptyTree() ObjectID {
+	return emptySha256Tree
+}
+func (Sha256ObjectFormatImpl) FullLength() int { return 64 }
+func (Sha256ObjectFormatImpl) IsValid(input string) bool {
+	return sha256Pattern.MatchString(input)
+}
+
+func (Sha256ObjectFormatImpl) MustID(b []byte) ObjectID {
+	var id Sha256Hash
+	copy(id[0:32], b)
+	return &id
+}
+
+// ComputeHash compute the hash for a given ObjectType and content
+func (h Sha256ObjectFormatImpl) ComputeHash(t ObjectType, content []byte) ObjectID {
+	var obj Sha256Hash
+	computeHash(obj[:0], sha256.New(), t, content)
+	return &obj
+}
+
+var (
+	Sha1ObjectFormat   ObjectFormat = Sha1ObjectFormatImpl{}
+	Sha256ObjectFormat ObjectFormat = Sha256ObjectFormatImpl{}
+	// any addition must be reflected in IsEmptyCommitID
+)
+
+var SupportedObjectFormats = []ObjectFormat{
+	Sha1ObjectFormat,
+}
+
+func ObjectFormatFromName(name string) ObjectFormat {
+	for _, objectFormat := range SupportedObjectFormats {
+		if name == objectFormat.Name() {
+			return objectFormat
+		}
+	}
+	return nil
+}
+
+func IsValidObjectFormat(name string) bool {
+	return ObjectFormatFromName(name) != nil
+}