object: Add basic object code

1 files changed, 89 insertions, 0 deletions

diff --git a/object/object.go b/object/object.go
new file mode 100644
index 00000000..c40769a7
--- /dev/null
+++ b/object/object.go
@@ -0,0 +1,89 @@
+// Package object provides Git object models and codecs.
+package object
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"strconv"
+)
+
+var (
+	// ErrInvalidObject indicates malformed serialized data.
+	ErrInvalidObject = errors.New("object: invalid object encoding")
+	// ErrNotFound indicates missing entries in in-memory lookups.
+	ErrNotFound = errors.New("object: not found")
+)
+
+// Type mirrors Git object type tags.
+type Type uint8
+
+const (
+	TypeInvalid  Type = 0
+	TypeCommit   Type = 1
+	TypeTree     Type = 2
+	TypeBlob     Type = 3
+	TypeTag      Type = 4
+	TypeFuture   Type = 5
+	TypeOfsDelta Type = 6
+	TypeRefDelta Type = 7
+)
+
+const (
+	typeNameBlob   = "blob"
+	typeNameTree   = "tree"
+	typeNameCommit = "commit"
+	typeNameTag    = "tag"
+)
+
+// Object is a Git object that can serialize itself.
+type Object interface {
+	ObjectType() Type
+	Serialize() ([]byte, error)
+}
+
+// ParseTypeName parses a canonical Git object type name.
+func ParseTypeName(name string) (Type, error) {
+	switch name {
+	case typeNameBlob:
+		return TypeBlob, nil
+	case typeNameTree:
+		return TypeTree, nil
+	case typeNameCommit:
+		return TypeCommit, nil
+	case typeNameTag:
+		return TypeTag, nil
+	default:
+		return TypeInvalid, ErrInvalidObject
+	}
+}
+
+func typeName(ty Type) (string, error) {
+	switch ty {
+	case TypeBlob:
+		return typeNameBlob, nil
+	case TypeTree:
+		return typeNameTree, nil
+	case TypeCommit:
+		return typeNameCommit, nil
+	case TypeTag:
+		return typeNameTag, nil
+	default:
+		return "", fmt.Errorf("object: unsupported type %d", ty)
+	}
+}
+
+func headerForType(ty Type, body []byte) ([]byte, error) {
+	tyStr, err := typeName(ty)
+	if err != nil {
+		return nil, err
+	}
+	size := strconv.Itoa(len(body))
+	var buf bytes.Buffer
+	buf.Grow(len(tyStr) + len(size) + 2)
+	buf.WriteString(tyStr)
+	buf.WriteByte(' ')
+	buf.WriteString(size)
+	buf.WriteByte(0)
+	return buf.Bytes(), nil
+}