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package glacier
import (
"crypto/sha256"
"io"
"github.com/aws/aws-sdk-go/internal/sdkio"
)
const bufsize = 1024 * 1024
// Hash contains information about the tree-hash and linear hash of a
// Glacier payload. This structure is generated by ComputeHashes().
type Hash struct {
TreeHash []byte
LinearHash []byte
}
// ComputeHashes computes the tree-hash and linear hash of a seekable reader r.
//
// See http://docs.aws.amazon.com/amazonglacier/latest/dev/checksum-calculations.html for more information.
func ComputeHashes(r io.ReadSeeker) Hash {
start, _ := r.Seek(0, sdkio.SeekCurrent) // Read the whole stream
defer r.Seek(start, sdkio.SeekStart) // Rewind stream at end
buf := make([]byte, bufsize)
hashes := [][]byte{}
hsh := sha256.New()
for {
// Build leaf nodes in 1MB chunks
n, err := io.ReadAtLeast(r, buf, bufsize)
if n == 0 {
break
}
tmpHash := sha256.Sum256(buf[:n])
hashes = append(hashes, tmpHash[:])
hsh.Write(buf[:n]) // Track linear hash while we're at it
if err != nil {
break // This is the last chunk
}
}
return Hash{
LinearHash: hsh.Sum(nil),
TreeHash: ComputeTreeHash(hashes),
}
}
// ComputeTreeHash builds a tree hash root node given a slice of
// hashes. Glacier tree hash to be derived from SHA256 hashes of 1MB
// chucks of the data.
//
// See http://docs.aws.amazon.com/amazonglacier/latest/dev/checksum-calculations.html for more information.
func ComputeTreeHash(hashes [][]byte) []byte {
hashCount := len(hashes)
switch hashCount {
case 0:
return nil
case 1:
return hashes[0]
}
leaves := make([][32]byte, hashCount)
for i := range leaves {
copy(leaves[i][:], hashes[i])
}
var (
queue = leaves[:0]
h256 = sha256.New()
buf [32]byte
)
for len(leaves) > 1 {
for i := 0; i < len(leaves); i += 2 {
if i+1 == len(leaves) {
queue = append(queue, leaves[i])
break
}
h256.Write(leaves[i][:])
h256.Write(leaves[i+1][:])
h256.Sum(buf[:0])
queue = append(queue, buf)
h256.Reset()
}
leaves = queue
queue = queue[:0]
}
return leaves[0][:]
}
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