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go/src/infra/libs/git/objectID.go

Index: go/src/infra/libs/git/objectID.go
diff --git a/go/src/infra/libs/git/objectID.go b/go/src/infra/libs/git/objectID.go
new file mode 100644
index 0000000000000000000000000000000000000000..b43a342ee712acfc005caadb89413eae019aee20
--- /dev/null
+++ b/go/src/infra/libs/git/objectID.go
@@ -0,0 +1,90 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package git
+
+import (
+	"crypto/sha1"
+	"encoding/hex"
+	"fmt"
+)
+
+// Types ///////////////////////////////////////////////////////////////////////
+
+// ObjectID is an immutable 20-byte git-sha for any Object type.
+// This is a struct instead of a straight simple type so that external users
+// may not manipulate the byte content directly.
+type ObjectID struct {
+	raw [20]byte
+}
+
+// Constants ///////////////////////////////////////////////////////////////////
+
+// The empty ObjectID (all zeros)
+var NoID = ObjectID{}
+
+// Constructors  ///////////////////////////////////////////////////////////////
+
+// MakeObjectIDForData hashes |data| as the git type |typ| (blob, commit, tree),
+// and returns an ObjectID for it.
+func MakeObjectIDForData(typ ObjectType, data []byte) *ObjectID {
+	h := sha1.New()
+	h.Write([]byte(fmt.Sprintf("%s %d\x00", typ, len(data))))
+	h.Write(data)
+	buf := [20]byte{}
+	h.Sum(buf[:0]) // Sum APPENDS to the slice.
+	return MakeObjectIDRaw(buf)
+}
+
+// MakeObjectIDRawErr treats |raw| as a 20-byte Id. panic()'s if len(raw) is not 20
+func MakeObjectIDRawErr(raw []byte) (*ObjectID, error) {
+	if len(raw) != 20 {
+		return nil, fmt.Errorf(
+			"MakeObjectIdRawErr() must be invoked with a 20 byte string, got %#v",
+			raw)
+	}
+	ret := &ObjectID{}
+	copy(ret.raw[:], raw)
+	return ret, nil
+}
+
+func MakeObjectIDRaw(raw [20]byte) *ObjectID {
+	ret := &ObjectID{}
+	copy(ret.raw[:], raw[:])
+	return ret
+}
+
+// MakeObjectID decodes the 40-byte |hexval| into an ObjectID. error's if
+// if it is not valid hexadecimal or the decoded value's length is not 20
+func MakeObjectIDErr(hexval string) (*ObjectID, error) {
+	raw, err := hex.DecodeString(hexval)
+	if err != nil {
+		return nil, err
+	}
+	return MakeObjectIDRawErr(raw)
+}
+
+func MakeObjectID(hexval string) *ObjectID {
+	r, err := MakeObjectIDErr(hexval)
+	if err != nil {
+		panic(err)
+	}
+	return r
+}
+
+// Member functions ////////////////////////////////////////////////////////////
+
+func (o *ObjectID) ID() *ObjectID { return o }
+func (o *ObjectID) String() string {
+	if *o != NoID {
+		return hex.EncodeToString(o.raw[:])
+	}
+	return "<NoID>"
+}
+
+// RawString returns a git hash-object compatible (binary) representation
+// of the ObjectID (e.g. suitable for inclusion in a tree object output)
+func (o *ObjectID) RawString() string {
+	return string(o.raw[:])
+}