git/odb: introduce odb.Storer interface

git/odb/storer.go

@@ -0,0 +1,16 @@
+package odb
+
+import "io"
+
+// Storer implements a storage engine for reading, writing, and creating
+// io.ReadWriters that can store information about loose objects
+type Storer interface {
+	// Open returns a handle on an existing object keyed by the given SHA.
+	// It returns an error if that file does not already exist.
+	Open(sha []byte) (f io.ReadWriteCloser, err error)
+
+	// Create returns a handle on a new object keyed by the given SHA. It
+	// returns an error if that file already exists (acting as if the
+	// `os.O_EXCL` mode is given in a bitmask to os.Open.
+	Create(sha []byte) (f io.ReadWriteCloser, err error)
+}