135 lines
3.3 KiB
Go
135 lines
3.3 KiB
Go
// Package mrhash implements the mailru hash, which is a modified SHA1.
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// If file size is less than or equal to the SHA1 block size (20 bytes),
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// its hash is simply its data right-padded with zero bytes.
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// Hash sum of a larger file is computed as a SHA1 sum of the file data
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// bytes concatenated with a decimal representation of the data length.
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package mrhash
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import (
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"crypto/sha1"
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"encoding"
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"encoding/hex"
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"errors"
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"hash"
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"strconv"
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)
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const (
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// BlockSize of the checksum in bytes.
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BlockSize = sha1.BlockSize
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// Size of the checksum in bytes.
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Size = sha1.Size
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startString = "mrCloud"
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hashError = "hash function returned error"
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)
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// Global errors
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var (
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ErrorInvalidHash = errors.New("invalid hash")
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)
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type digest struct {
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total int // bytes written into hash so far
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sha hash.Hash // underlying SHA1
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small []byte // small content
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}
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// New returns a new hash.Hash computing the Mailru checksum.
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func New() hash.Hash {
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d := &digest{}
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d.Reset()
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return d
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}
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// Write writes len(p) bytes from p to the underlying data stream. It returns
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// the number of bytes written from p (0 <= n <= len(p)) and any error
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// encountered that caused the write to stop early. Write must return a non-nil
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// error if it returns n < len(p). Write must not modify the slice data, even
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// temporarily.
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//
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// Implementations must not retain p.
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func (d *digest) Write(p []byte) (n int, err error) {
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n, err = d.sha.Write(p)
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if err != nil {
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panic(hashError)
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}
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d.total += n
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if d.total <= Size {
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d.small = append(d.small, p...)
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}
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return n, nil
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}
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// Sum appends the current hash to b and returns the resulting slice.
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// It does not change the underlying hash state.
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func (d *digest) Sum(b []byte) []byte {
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// If content is small, return it padded to Size
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if d.total <= Size {
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padded := make([]byte, Size)
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copy(padded, d.small)
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return append(b, padded...)
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}
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endString := strconv.Itoa(d.total)
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copy, err := cloneSHA1(d.sha)
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if err == nil {
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_, err = copy.Write([]byte(endString))
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}
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if err != nil {
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panic(hashError)
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}
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return copy.Sum(b)
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}
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// cloneSHA1 clones state of SHA1 hash
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func cloneSHA1(orig hash.Hash) (clone hash.Hash, err error) {
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state, err := orig.(encoding.BinaryMarshaler).MarshalBinary()
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if err != nil {
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return nil, err
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}
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clone = sha1.New()
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err = clone.(encoding.BinaryUnmarshaler).UnmarshalBinary(state)
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return
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}
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// Reset resets the Hash to its initial state.
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func (d *digest) Reset() {
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d.sha = sha1.New()
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_, _ = d.sha.Write([]byte(startString))
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d.total = 0
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}
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// Size returns the number of bytes Sum will return.
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func (d *digest) Size() int {
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return Size
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}
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// BlockSize returns the hash's underlying block size.
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// The Write method must be able to accept any amount
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// of data, but it may operate more efficiently if all writes
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// are a multiple of the block size.
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func (d *digest) BlockSize() int {
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return BlockSize
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}
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// Sum returns the Mailru checksum of the data.
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func Sum(data []byte) []byte {
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var d digest
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d.Reset()
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_, _ = d.Write(data)
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return d.Sum(nil)
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}
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// DecodeString converts a string to the Mailru hash
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func DecodeString(s string) ([]byte, error) {
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b, err := hex.DecodeString(s)
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if err != nil || len(b) != Size {
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return nil, ErrorInvalidHash
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}
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return b, nil
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}
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// must implement this interface
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var (
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_ hash.Hash = (*digest)(nil)
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)
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