Added Hasher for computing hashes of streamed objects

core/hash.go

@@ -3,6 +3,7 @@ package core
 import (
 	"crypto/sha1"
 	"encoding/hex"
+	"hash"
 	"strconv"
 )
 
@@ -14,13 +15,9 @@ var ZeroHash Hash
 
 // ComputeHash compute the hash for a given ObjectType and content
 func ComputeHash(t ObjectType, content []byte) Hash {
-	h := t.Bytes()
-	h = append(h, ' ')
-	h = strconv.AppendInt(h, int64(len(content)), 10)
-	h = append(h, 0)
-	h = append(h, content...)
-
-	return Hash(sha1.Sum(h))
+	h := NewHasher(t, int64(len(content)))
+	h.Write(content)
+	return h.Sum()
 }
 
 // NewHash return a new Hash from a hexadecimal hash representation
@@ -41,3 +38,21 @@ func (h Hash) IsZero() bool {
 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
+}

core/hash_test.go

@@ -33,3 +33,10 @@ func (s *HashSuite) TestIsZero(c *C) {
 	hash = NewHash("8ab686eafeb1f44702738c8b0f24f2567c36da6d")
 	c.Assert(hash.IsZero(), Equals, false)
 }
+
+func (s *HashSuite) TestNewHasher(c *C) {
+	content := "hasher test sample"
+	hasher := NewHasher(BlobObject, int64(len(content)))
+	hasher.Write([]byte(content))
+	c.Assert(hasher.Sum().String(), Equals, "dc42c3cc80028d0ec61f0a6b24cadd1c195c4dfc")
+}