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path: root/zsig/sum.go
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package zsig

import (
	"bytes"
	"crypto/sha512"
	"errors"
	"io"
	"log"
)

const (
	Alg       = "SHA512/256"
	BlockSize = 65536
)

func (z ZHeader) Verify(r io.Reader) error {
	h := sha512.New512_256() // from z.Alg
	blockCount := len(z.Sums)
	for _, sum := range z.Sums {
		h.Reset()
		_, err := io.CopyN(h, r, z.BlockSize)
		if err != nil && err != io.EOF {
			return err
		}
		if !bytes.Equal(sum, h.Sum(nil)) {
			return errors.New("sum mismatch")
		}
		blockCount--
	}
	if blockCount != 0 {
		log.Println(blockCount)
		return errors.New("len mismatch")
	}
	return nil
}