Extract several packages to form a public API

framework/buffer/bytesreader.go

@@ -0,0 +1,43 @@
+package buffer
+
+import (
+	"bytes"
+)
+
+// BytesReader is a wrapper for bytes.Reader that stores the original []byte
+// value and allows to retrieve it.
+//
+// It is meant for passing to libraries that expect a io.Reader
+// but apply certain optimizations when the Reader implements
+// Bytes() interface.
+type BytesReader struct {
+	*bytes.Reader
+	value []byte
+}
+
+// Bytes returns the unread portion of underlying slice used to construct
+// BytesReader.
+func (br BytesReader) Bytes() []byte {
+	return br.value[int(br.Size())-br.Len():]
+}
+
+// Copy returns the BytesReader reading from the same slice as br at the same
+// position.
+func (br BytesReader) Copy() BytesReader {
+	return NewBytesReader(br.Bytes())
+}
+
+// Close is a dummy method for implementation of io.Closer so BytesReader can
+// be used in MemoryBuffer directly.
+func (br BytesReader) Close() error {
+	return nil
+}
+
+func NewBytesReader(b []byte) BytesReader {
+	// BytesReader and not *BytesReader because BytesReader already wraps two
+	// pointers and double indirection would be pointless.
+	return BytesReader{
+		Reader: bytes.NewReader(b),
+		value:  b,
+	}
+}