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hash.go
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hash.go
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package object
import (
"crypto/md5"
"encoding/hex"
"fmt"
"io"
)
type Hash struct {
Size int64
PartSize int64
Hash string
}
func (h Hash) String() string {
return fmt.Sprintf("%d.%d.%s", h.Size, h.PartSize, h.Hash)
}
func GenerateHash(o Object) (*Hash, error) {
var h Hash
err := o.Open(func(r io.Reader) error {
m := md5.New()
size, err := io.Copy(m, r)
if err != nil {
return err
}
h = Hash{size, 0, hex.EncodeToString(m.Sum(nil))}
return nil
})
return &h, err
}
func matchHash(o1, o2 Object) (bool, error) {
h1, err := o1.Hash()
if err != nil {
return false, err
}
h2, err := o2.Hash()
if err != nil {
return false, err
}
if h2.PartSize != 0 {
panic("unimplemented")
}
if h1.Size != h2.Size {
return false, nil
}
if h1.PartSize == 0 {
return h1.Hash == h2.Hash, nil
}
var hash2 string
err = o2.Open(func(r io.Reader) error {
var err error
// this is an implementation of the AWS S3 multipart upload hashing
// algorithm, documented at
// https://docs.aws.amazon.com/AmazonS3/latest/userguide/checking-object-integrity.html#large-object-checksums
partCount := int(h1.Size / h1.PartSize)
i := 0
h2 := md5.New()
for err == nil {
i++
h := md5.New()
_, err = io.CopyN(h, r, h1.PartSize)
if err == nil || err == io.EOF {
sum := h.Sum(nil)
h2.Write(sum)
}
// don't loop forever
if err == nil && i > partCount+1 {
err = io.EOF
}
}
if err != io.EOF {
return err
}
hash2 = fmt.Sprintf("%x-%d", h2.Sum(nil), i)
return nil
})
if err != nil {
return false, err
}
return h1.Hash == hash2, nil
}