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58 lines
1.7 KiB
Go
58 lines
1.7 KiB
Go
// Copyright (C) 2023 mieru authors
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <https://www.gnu.org/licenses/>
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package protocol
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import (
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crand "crypto/rand"
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"fmt"
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mrand "math/rand"
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"github.com/enfein/mieru/pkg/rng"
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"github.com/enfein/mieru/pkg/util"
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)
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var (
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recommendedConsecutiveASCIILen = 32 + rng.FixedInt(17)
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)
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type paddingOpts struct {
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// The maxinum length of padding.
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maxLen int
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// The mininum length of consecutive ASCII characters.
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// This implies the mininum length of padding.
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minConsecutiveASCIILen int
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}
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func newPadding(opts paddingOpts) []byte {
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if opts.maxLen < opts.minConsecutiveASCIILen {
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panic(fmt.Sprintf("Invalid padding options: maxLen %d is smaller than minConsecutiveASCIILen %d", opts.maxLen, opts.minConsecutiveASCIILen))
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}
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length := rng.Intn(opts.maxLen-opts.minConsecutiveASCIILen+1) + opts.minConsecutiveASCIILen
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p := make([]byte, length)
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for {
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if _, err := crand.Read(p); err == nil {
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break
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}
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}
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beginIdx := 0
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if length > opts.minConsecutiveASCIILen {
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beginIdx = mrand.Intn(length - opts.minConsecutiveASCIILen)
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}
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util.ToPrintableChar(p, beginIdx, beginIdx+opts.minConsecutiveASCIILen)
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return p
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}
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