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spamsumwriter.go
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spamsumwriter.go
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// Copyright 2013, Michiel Buddingh, All rights reserved.
// Use of this code is governed by version 2.0 or later of the Apache
// License, available at http://www.apache.org/licenses/LICENSE-2.0
package spamsum
import (
// "hash"
)
type SpamSumWriter struct {
SpamSum
spamsumState
}
// StartFixedBlocksize creates a SpamSumWriter with a fixed block size,
// that implements the hash.Hash interface, and accepts an arbitrary
// number of bytes through Write(). Note that the SpamSum algorithm
// does not handle arbitrary length inputs well. If the input stream
// is significantly longer than SpamLength * blocksize, the tail end
// of the stream will, for most intents and purposes, not generate
// hash blocks. Please consider the HashBytes or HashReadSeeker
// functions instead.
func StartFixedBlocksize(blockSize uint32) *SpamSumWriter {
sum := new(SpamSumWriter)
sum.SpamSum.reset()
sum.spamsumState.reset()
sum.blocksize = blockSize
return sum
}
// Reset sets the state of the SpamSumWriter to its initial value,
// while keeping the blocksize parameter as is.
func (sss *SpamSumWriter) Reset() {
sss.spamsumState.reset()
sss.SpamSum.reset()
}
func (sss *SpamSumWriter) Size() int {
return SpamsumLength
}
// Write a byte slice to the SpamSumWriter. Returns the length of the
// byte slice, and nil.
func (sss *SpamSumWriter) Write(block []byte) (int, error) {
processBlock(block, len(block), &sss.spamsumState, &sss.SpamSum)
return len(block), nil
}
func (sss *SpamSumWriter) String() (result string) {
writeTail(&sss.spamsumState, &sss.SpamSum)
result = sss.SpamSum.String()
return
}
// Sum is implemented mostly for the sake of compatibility with
// hash.Hash. While the SpamSum algorithm creates variable-length
// hashes, Sum is supposed to return a fixed-length slice of Size()
// bytes. The implementation returns a slice where the non-zero bytes
// contain a base64-encoded 6-bit hash for a `BlockSize()`-sized
// block. The block hashes continue up to the end of the slice, or up
// to the first zero byte.
func (sss *SpamSumWriter) Sum(block []byte) (result []byte) {
var cloneState spamsumState = sss.spamsumState
var cloneSum SpamSum = sss.SpamSum
processBlock(block, len(block), &cloneState, &cloneSum)
writeTail(&cloneState, &cloneSum)
result = make([]byte, SpamsumLength)
copy(result, cloneSum.leftPart[:cloneSum.leftIndex])
return
}