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package gitio
import (
"bytes"
"crypto/sha1"
"fmt"
"hash"
"io"
)
// HashfileReader reads and verifies Git "hashfiles" as defined in
// https://github.com/git/git/blob/v2.21.0/csum-file.h.
type HashfileReader struct {
tr *TrailerReader
tee io.Reader
sum hash.Hash
}
// NewHashfileReader wraps r to return a reader that will omit the
// trailing checksum. When the HashfileReader reaches EOF it will
// transparently compare the actual checksum, as calculated while
// reading, to the expected checksum provided by the trailer of r.
func NewHashfileReader(r io.Reader) *HashfileReader {
sum := sha1.New()
tr := NewTrailerReader(r, sum.Size())
return &HashfileReader{
tr: tr,
tee: io.TeeReader(tr, sum),
sum: sum,
}
}
func (hr *HashfileReader) Read(p []byte) (int, error) {
n, err := hr.tee.Read(p)
if err == io.EOF {
return n, hr.validateChecksum()
}
return n, err
}
func (hr *HashfileReader) validateChecksum() error {
trailer, err := hr.tr.Trailer()
if err != nil {
return err
}
if actualSum := hr.sum.Sum(nil); !bytes.Equal(trailer, actualSum) {
return fmt.Errorf("hashfile checksum mismatch: expected %x got %x", trailer, actualSum)
}
return io.EOF
}
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