72 lines
1.5 KiB
Go
72 lines
1.5 KiB
Go
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package glacier
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import (
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"crypto/sha256"
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"io"
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)
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const bufsize = 1024 * 1024
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// Hash contains information about the tree-hash and linear hash of a
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// Glacier payload. This structure is generated by ComputeHashes().
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type Hash struct {
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TreeHash []byte
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LinearHash []byte
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}
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// ComputeHashes computes the tree-hash and linear hash of a seekable reader r.
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func ComputeHashes(r io.ReadSeeker) Hash {
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r.Seek(0, 0) // Read the whole stream
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defer r.Seek(0, 0) // Rewind stream at end
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buf := make([]byte, bufsize)
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hashes := [][]byte{}
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hsh := sha256.New()
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for {
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// Build leaf nodes in 1MB chunks
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n, err := io.ReadAtLeast(r, buf, bufsize)
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if n == 0 {
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break
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}
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tmpHash := sha256.Sum256(buf[:n])
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hashes = append(hashes, tmpHash[:])
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hsh.Write(buf[:n]) // Track linear hash while we're at it
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if err != nil {
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break // This is the last chunk
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}
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}
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return Hash{
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LinearHash: hsh.Sum(nil),
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TreeHash: buildHashTree(hashes),
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}
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}
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// buildHashTree builds a hash tree root node given a set of hashes.
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func buildHashTree(hashes [][]byte) []byte {
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if hashes == nil || len(hashes) == 0 {
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return nil
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}
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for len(hashes) > 1 {
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tmpHashes := [][]byte{}
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for i := 0; i < len(hashes); i += 2 {
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if i+1 <= len(hashes)-1 {
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tmpHash := append(append([]byte{}, hashes[i]...), hashes[i+1]...)
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tmpSum := sha256.Sum256(tmpHash)
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tmpHashes = append(tmpHashes, tmpSum[:])
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} else {
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tmpHashes = append(tmpHashes, hashes[i])
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}
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}
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hashes = tmpHashes
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}
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return hashes[0]
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}
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