hashing: move to repository package

internal/repository/hashing/reader.go

@@ -0,0 +1,28 @@
+package hashing
+
+import (
+	"hash"
+	"io"
+)
+
+// A Reader hashes all data read from the underlying reader.
+type Reader struct {
+	r io.Reader
+	h hash.Hash
+}
+
+// NewReader returns a new Reader that uses the hash h.
+func NewReader(r io.Reader, h hash.Hash) *Reader {
+	return &Reader{r: r, h: h}
+}
+
+func (h *Reader) Read(p []byte) (int, error) {
+	n, err := h.r.Read(p)
+	_, _ = h.h.Write(p[:n]) // Never returns an error.
+	return n, err
+}
+
+// Sum returns the hash of the data read so far.
+func (h *Reader) Sum(d []byte) []byte {
+	return h.h.Sum(d)
+}