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buffer.go
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buffer.go
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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ssh
import (
"io"
"sync"
)
// readbuf provides a linked list readbuf for data exchange
// between producer and consumer. Theoretically the readbuf is
// of unlimited capacity as it does no allocation of its own.
type readbuf struct {
// protects concurrent access to head, tail and eof
*sync.Cond
head *element // the readbuf that will be read first
tail *element // the readbuf that will be read last
eof bool //
}
// An element represents a single link in a linked list.
type element struct {
buf []byte
next *element
}
func newReadBuf() *readbuf {
e := new(element)
b := &readbuf{
Cond: sync.NewCond(new(sync.Mutex)),
head: e,
tail: e,
}
return b
}
// write makes buf available for Read to receive.
// buf must not be modified after the call to write.
func (b *readbuf) write(buf []byte) (int, error) {
b.Cond.L.Lock()
defer b.Cond.L.Unlock()
e := &element{buf: buf}
b.tail.next = e
b.tail = e
b.Cond.Signal()
return len(buf), nil
}
func (b *readbuf) close() {
b.Cond.L.Lock()
defer b.Cond.L.Unlock()
b.eof = true
b.Cond.Signal()
}
// read reads data from the internal readbuf in buf.
// Reads will block if not data is available, or until
// Close is called.
func (b *readbuf) read(buf []byte) (n int, err error) {
b.Cond.L.Lock()
defer b.Cond.L.Unlock()
for {
// if there is data in b.head, copy it
if len(b.head.buf) > 0 {
r := copy(buf, b.head.buf)
buf, b.head.buf = buf[r:], b.head.buf[r:]
n += r
if len(buf) == 0 {
// dest full
break
}
continue
}
// if there is a next readbuf, make it the head
if len(b.head.buf) == 0 && b.head != b.tail {
b.head = b.head.next
continue
}
// if at least one byte has been copied return
if n > 0 {
break
}
// out of readbufs, wait for producer
if b.eof {
err = io.EOF
break
}
b.Cond.Wait()
}
return
}