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// Copyright 2014 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 http2
import (
"errors"
"io"
"sync"
)
// pipe is a goroutine-safe io.Reader/io.Writer pair. It's like
// io.Pipe except there are no PipeReader/PipeWriter halves, and the
// underlying buffer is an interface. (io.Pipe is always unbuffered)
type pipe struct {
mu sync.Mutex
c sync.Cond // c.L lazily initialized to &p.mu
b pipeBuffer // nil when done reading
err error // read error once empty. non-nil means closed.
breakErr error // immediate read error (caller doesn't see rest of b)
donec chan struct{} // closed on error
readFn func() // optional code to run in Read before error
}
type pipeBuffer interface {
Len() int
io.Writer
io.Reader
}
func (p *pipe) Len() int {
p.mu.Lock()
defer p.mu.Unlock()
if p.b == nil {
return 0
}
return p.b.Len()
}
// Read waits until data is available and copies bytes
// from the buffer into p.
func (p *pipe) Read(d []byte) (n int, err error) {
p.mu.Lock()
defer p.mu.Unlock()
if p.c.L == nil {
p.c.L = &p.mu
}
for {
if p.breakErr != nil {
return 0, p.breakErr
}
if p.b != nil && p.b.Len() > 0 {
return p.b.Read(d)
}
if p.err != nil {
if p.readFn != nil {
p.readFn() // e.g. copy trailers
p.readFn = nil // not sticky like p.err
}
p.b = nil
return 0, p.err
}
p.c.Wait()
}
}
var errClosedPipeWrite = errors.New("write on closed buffer")
// Write copies bytes from p into the buffer and wakes a reader.
// It is an error to write more data than the buffer can hold.
func (p *pipe) Write(d []byte) (n int, err error) {
p.mu.Lock()
defer p.mu.Unlock()
if p.c.L == nil {
p.c.L = &p.mu
}
defer p.c.Signal()
if p.err != nil {
return 0, errClosedPipeWrite
}
if p.breakErr != nil {
return len(d), nil // discard when there is no reader
}
return p.b.Write(d)
}
// CloseWithError causes the next Read (waking up a current blocked
// Read if needed) to return the provided err after all data has been
// read.
//
// The error must be non-nil.
func (p *pipe) CloseWithError(err error) { p.closeWithError(&p.err, err, nil) }
// BreakWithError causes the next Read (waking up a current blocked
// Read if needed) to return the provided err immediately, without
// waiting for unread data.
func (p *pipe) BreakWithError(err error) { p.closeWithError(&p.breakErr, err, nil) }
// closeWithErrorAndCode is like CloseWithError but also sets some code to run
// in the caller's goroutine before returning the error.
func (p *pipe) closeWithErrorAndCode(err error, fn func()) { p.closeWithError(&p.err, err, fn) }
func (p *pipe) closeWithError(dst *error, err error, fn func()) {
if err == nil {
panic("err must be non-nil")
}
p.mu.Lock()
defer p.mu.Unlock()
if p.c.L == nil {
p.c.L = &p.mu
}
defer p.c.Signal()
if *dst != nil {
// Already been done.
return
}
p.readFn = fn
if dst == &p.breakErr {
p.b = nil
}
*dst = err
p.closeDoneLocked()
}
// requires p.mu be held.
func (p *pipe) closeDoneLocked() {
if p.donec == nil {
return
}
// Close if unclosed. This isn't racy since we always
// hold p.mu while closing.
select {
case <-p.donec:
default:
close(p.donec)
}
}
// Err returns the error (if any) first set by BreakWithError or CloseWithError.
func (p *pipe) Err() error {
p.mu.Lock()
defer p.mu.Unlock()
if p.breakErr != nil {
return p.breakErr
}
return p.err
}
// Done returns a channel which is closed if and when this pipe is closed
// with CloseWithError.
func (p *pipe) Done() <-chan struct{} {
p.mu.Lock()
defer p.mu.Unlock()
if p.donec == nil {
p.donec = make(chan struct{})
if p.err != nil || p.breakErr != nil {
// Already hit an error.
p.closeDoneLocked()
}
}
return p.donec
}
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