mirror of
https://github.com/xtaci/smux.git
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102 lines
2.9 KiB
Go
102 lines
2.9 KiB
Go
// MIT License
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//
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// Copyright (c) 2016-2017 xtaci
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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package smux
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import (
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"errors"
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"sync"
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)
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var (
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defaultAllocator *Allocator
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debruijnPos = [...]byte{0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31}
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)
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func init() {
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defaultAllocator = NewAllocator()
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}
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// Allocator for incoming frames, optimized to prevent overwriting after zeroing
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type Allocator struct {
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buffers []sync.Pool
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}
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// NewAllocator initiates a []byte allocator for frames less than 65536 bytes,
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// the waste(memory fragmentation) of space allocation is guaranteed to be
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// no more than 50%.
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func NewAllocator() *Allocator {
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alloc := new(Allocator)
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alloc.buffers = make([]sync.Pool, 17) // 1B -> 64K
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for k := range alloc.buffers {
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i := k
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alloc.buffers[k].New = func() any {
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b := make([]byte, 1<<uint32(i))
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return &b
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}
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}
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return alloc
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}
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// Get a []byte from pool with most appropriate cap
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func (alloc *Allocator) Get(size int) *[]byte {
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if size <= 0 || size > 65536 {
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return nil
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}
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bits := msb(size)
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if size == 1<<bits {
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p := alloc.buffers[bits].Get().(*[]byte)
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*p = (*p)[:size]
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return p
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}
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p := alloc.buffers[bits+1].Get().(*[]byte)
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*p = (*p)[:size]
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return p
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}
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// Put returns a []byte to pool for future use,
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// which the cap must be exactly 2^n
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func (alloc *Allocator) Put(p *[]byte) error {
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if p == nil {
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return errors.New("allocator Put() incorrect buffer size")
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}
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bits := msb(cap(*p))
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if cap(*p) == 0 || cap(*p) > 65536 || cap(*p) != 1<<bits {
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return errors.New("allocator Put() incorrect buffer size")
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}
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alloc.buffers[bits].Put(p)
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return nil
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}
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// msb returns the pos of most significant bit
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// http://supertech.csail.mit.edu/papers/debruijn.pdf
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func msb(size int) byte {
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v := uint32(size)
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v |= v >> 1
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v |= v >> 2
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v |= v >> 4
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v |= v >> 8
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v |= v >> 16
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return debruijnPos[(v*0x07C4ACDD)>>27]
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}
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