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package glacier
import (
"crypto/sha256"
"io"
)
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.
func ComputeHashes(r io.ReadSeeker) Hash {
r.Seek(0, 0) // Read the whole stream
defer r.Seek(0, 0) // 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: buildHashTree(hashes),
}
}
// buildHashTree builds a hash tree root node given a set of hashes.
func buildHashTree(hashes [][]byte) []byte {
if hashes == nil || len(hashes) == 0 {
return nil
}
for len(hashes) > 1 {
tmpHashes := [][]byte{}
for i := 0; i < len(hashes); i += 2 {
if i+1 <= len(hashes)-1 {
tmpHash := append(append([]byte{}, hashes[i]...), hashes[i+1]...)
tmpSum := sha256.Sum256(tmpHash)
tmpHashes = append(tmpHashes, tmpSum[:])
} else {
tmpHashes = append(tmpHashes, hashes[i])
}
}
hashes = tmpHashes
}
return hashes[0]
}
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