Rename HashReader -> HashAppendReader, add HashingReader

backend/reader.go

@@ -0,0 +1,73 @@
+package backend
+
+import (
+	"hash"
+	"io"
+)
+
+type HashAppendReader struct {
+	r      io.Reader
+	h      hash.Hash
+	sum    []byte
+	closed bool
+}
+
+func NewHashAppendReader(r io.Reader, h hash.Hash) *HashAppendReader {
+	return &HashAppendReader{
+		h:   h,
+		r:   io.TeeReader(r, h),
+		sum: make([]byte, 0, h.Size()),
+	}
+}
+
+func (h *HashAppendReader) Read(p []byte) (n int, err error) {
+	if !h.closed {
+		n, err = h.r.Read(p)
+
+		if err == io.EOF {
+			h.closed = true
+			h.sum = h.h.Sum(h.sum)
+		} else if err != nil {
+			return
+		}
+	}
+
+	if h.closed {
+		// output hash
+		r := len(p) - n
+
+		if r > 0 {
+			c := copy(p[n:], h.sum)
+			h.sum = h.sum[c:]
+
+			n += c
+			err = nil
+		}
+
+		if len(h.sum) == 0 {
+			err = io.EOF
+		}
+	}
+
+	return
+}
+
+type HashingReader struct {
+	r io.Reader
+	h hash.Hash
+}
+
+func NewHashingReader(r io.Reader, h hash.Hash) *HashingReader {
+	return &HashingReader{
+		h: h,
+		r: io.TeeReader(r, h),
+	}
+}
+
+func (h *HashingReader) Read(p []byte) (int, error) {
+	return h.r.Read(p)
+}
+
+func (h *HashingReader) Sum(d []byte) []byte {
+	return h.h.Sum(d)
+}