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98 lines
2.1 KiB
Go
98 lines
2.1 KiB
Go
2 years ago
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// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package ssh
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import (
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"io"
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"sync"
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)
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// buffer provides a linked list buffer for data exchange
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// between producer and consumer. Theoretically the buffer is
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// of unlimited capacity as it does no allocation of its own.
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type buffer struct {
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// protects concurrent access to head, tail and closed
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*sync.Cond
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head *element // the buffer that will be read first
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tail *element // the buffer that will be read last
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closed bool
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}
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// An element represents a single link in a linked list.
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type element struct {
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buf []byte
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next *element
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}
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// newBuffer returns an empty buffer that is not closed.
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func newBuffer() *buffer {
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e := new(element)
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b := &buffer{
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Cond: newCond(),
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head: e,
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tail: e,
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}
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return b
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}
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// write makes buf available for Read to receive.
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// buf must not be modified after the call to write.
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func (b *buffer) write(buf []byte) {
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b.Cond.L.Lock()
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e := &element{buf: buf}
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b.tail.next = e
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b.tail = e
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b.Cond.Signal()
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b.Cond.L.Unlock()
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}
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// eof closes the buffer. Reads from the buffer once all
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// the data has been consumed will receive io.EOF.
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func (b *buffer) eof() {
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b.Cond.L.Lock()
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b.closed = true
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b.Cond.Signal()
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b.Cond.L.Unlock()
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}
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// Read reads data from the internal buffer in buf. Reads will block
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// if no data is available, or until the buffer is closed.
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func (b *buffer) Read(buf []byte) (n int, err error) {
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b.Cond.L.Lock()
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defer b.Cond.L.Unlock()
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for len(buf) > 0 {
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// if there is data in b.head, copy it
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if len(b.head.buf) > 0 {
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r := copy(buf, b.head.buf)
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buf, b.head.buf = buf[r:], b.head.buf[r:]
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n += r
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continue
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}
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// if there is a next buffer, make it the head
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if len(b.head.buf) == 0 && b.head != b.tail {
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b.head = b.head.next
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continue
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}
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// if at least one byte has been copied, return
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if n > 0 {
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break
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}
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// if nothing was read, and there is nothing outstanding
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// check to see if the buffer is closed.
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if b.closed {
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err = io.EOF
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break
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}
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// out of buffers, wait for producer
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b.Cond.Wait()
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}
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return
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}
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