1 files changed, 58 insertions, 0 deletions
diff --git a/plumbing/hash.go b/plumbing/hash.go
new file mode 100644
index 0000000..7fa953d
--- /dev/null
+++ b/plumbing/hash.go
@@ -0,0 +1,58 @@
+package plumbing
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"hash"
+	"strconv"
+)
+
+// Hash SHA1 hased content
+type Hash [20]byte
+
+// ZeroHash is Hash with value zero
+var ZeroHash Hash
+
+// ComputeHash compute the hash for a given ObjectType and content
+func ComputeHash(t ObjectType, content []byte) Hash {
+	h := NewHasher(t, int64(len(content)))
+	h.Write(content)
+	return h.Sum()
+}
+
+// NewHash return a new Hash from a hexadecimal hash representation
+func NewHash(s string) Hash {
+	b, _ := hex.DecodeString(s)
+
+	var h Hash
+	copy(h[:], b)
+
+	return h
+}
+
+func (h Hash) IsZero() bool {
+	var empty Hash
+	return h == empty
+}
+
+func (h Hash) String() string {
+	return hex.EncodeToString(h[:])
+}
+
+type Hasher struct {
+	hash.Hash
+}
+
+func NewHasher(t ObjectType, size int64) Hasher {
+	h := Hasher{sha1.New()}
+	h.Write(t.Bytes())
+	h.Write([]byte(" "))
+	h.Write([]byte(strconv.FormatInt(size, 10)))
+	h.Write([]byte{0})
+	return h
+}
+
+func (h Hasher) Sum() (hash Hash) {
+	copy(hash[:], h.Hash.Sum(nil))
+	return
+}