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. // // See http://docs.aws.amazon.com/amazonglacier/latest/dev/checksum-calculations.html for more information. 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: 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 { 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] }