restic/backend/writer.go

package backend

import (
	"hash"
	"io"
)

// HashingWriter wraps an io.Writer to hashes all data that is written to it.
type HashingWriter struct {
	w    io.Writer
	h    hash.Hash
	size int
}

// NewHashAppendWriter wraps the writer w and feeds all data written to the hash h.
func NewHashingWriter(w io.Writer, h hash.Hash) *HashingWriter {
	return &HashingWriter{
		h: h,
		w: io.MultiWriter(w, h),
	}
}

// Write wraps the write method of the underlying writer and also hashes all data.
func (h *HashingWriter) Write(p []byte) (int, error) {
	n, err := h.w.Write(p)
	h.size += n
	return n, err
}

// Sum returns the hash of all data written so far.
func (h *HashingWriter) Sum(d []byte) []byte {
	return h.h.Sum(d)
}

// Size returns the number of bytes written to the underlying writer.
func (h *HashingWriter) Size() int {
	return h.size
}