mirror of
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207 lines
5.1 KiB
Go
207 lines
5.1 KiB
Go
// Copyright 2009 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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// Pipe adapter to connect code expecting an io.Reader
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// with code expecting an io.Writer.
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package io
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import (
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"errors"
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"sync"
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)
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// onceError is an object that will only store an error once.
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type onceError struct {
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sync.Mutex // guards following
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err error
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}
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func (a *onceError) Store(err error) {
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a.Lock()
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defer a.Unlock()
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if a.err != nil {
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return
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}
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a.err = err
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}
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func (a *onceError) Load() error {
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a.Lock()
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defer a.Unlock()
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return a.err
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}
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// ErrClosedPipe is the error used for read or write operations on a closed pipe.
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var ErrClosedPipe = errors.New("io: read/write on closed pipe")
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// A pipe is the shared pipe structure underlying PipeReader and PipeWriter.
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type pipe struct {
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wrMu sync.Mutex // Serializes Write operations
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wrCh chan []byte
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rdCh chan int
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once sync.Once // Protects closing done
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done chan struct{}
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rerr onceError
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werr onceError
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}
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func (p *pipe) read(b []byte) (n int, err error) {
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select {
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case <-p.done:
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return 0, p.readCloseError()
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default:
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}
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select {
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case bw := <-p.wrCh:
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nr := copy(b, bw)
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p.rdCh <- nr
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return nr, nil
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case <-p.done:
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return 0, p.readCloseError()
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}
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}
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func (p *pipe) closeRead(err error) error {
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if err == nil {
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err = ErrClosedPipe
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}
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p.rerr.Store(err)
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p.once.Do(func() { close(p.done) })
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return nil
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}
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func (p *pipe) write(b []byte) (n int, err error) {
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select {
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case <-p.done:
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return 0, p.writeCloseError()
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default:
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p.wrMu.Lock()
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defer p.wrMu.Unlock()
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}
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for once := true; once || len(b) > 0; once = false {
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select {
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case p.wrCh <- b:
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nw := <-p.rdCh
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b = b[nw:]
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n += nw
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case <-p.done:
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return n, p.writeCloseError()
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}
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}
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return n, nil
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}
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func (p *pipe) closeWrite(err error) error {
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if err == nil {
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err = EOF
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}
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p.werr.Store(err)
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p.once.Do(func() { close(p.done) })
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return nil
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}
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// readCloseError is considered internal to the pipe type.
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func (p *pipe) readCloseError() error {
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rerr := p.rerr.Load()
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if werr := p.werr.Load(); rerr == nil && werr != nil {
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return werr
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}
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return ErrClosedPipe
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}
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// writeCloseError is considered internal to the pipe type.
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func (p *pipe) writeCloseError() error {
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werr := p.werr.Load()
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if rerr := p.rerr.Load(); werr == nil && rerr != nil {
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return rerr
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}
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return ErrClosedPipe
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}
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// A PipeReader is the read half of a pipe.
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type PipeReader struct {
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p *pipe
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}
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// Read implements the standard Read interface:
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// it reads data from the pipe, blocking until a writer
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// arrives or the write end is closed.
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// If the write end is closed with an error, that error is
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// returned as err; otherwise err is EOF.
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func (r *PipeReader) Read(data []byte) (n int, err error) {
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return r.p.read(data)
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}
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// Close closes the reader; subsequent writes to the
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// write half of the pipe will return the error ErrClosedPipe.
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func (r *PipeReader) Close() error {
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return r.CloseWithError(nil)
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}
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// CloseWithError closes the reader; subsequent writes
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// to the write half of the pipe will return the error err.
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//
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// CloseWithError never overwrites the previous error if it exists
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// and always returns nil.
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func (r *PipeReader) CloseWithError(err error) error {
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return r.p.closeRead(err)
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}
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// A PipeWriter is the write half of a pipe.
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type PipeWriter struct {
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p *pipe
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}
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// Write implements the standard Write interface:
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// it writes data to the pipe, blocking until one or more readers
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// have consumed all the data or the read end is closed.
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// If the read end is closed with an error, that err is
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// returned as err; otherwise err is ErrClosedPipe.
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func (w *PipeWriter) Write(data []byte) (n int, err error) {
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return w.p.write(data)
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}
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// Close closes the writer; subsequent reads from the
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// read half of the pipe will return no bytes and EOF.
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func (w *PipeWriter) Close() error {
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return w.CloseWithError(nil)
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}
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// CloseWithError closes the writer; subsequent reads from the
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// read half of the pipe will return no bytes and the error err,
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// or EOF if err is nil.
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//
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// CloseWithError never overwrites the previous error if it exists
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// and always returns nil.
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func (w *PipeWriter) CloseWithError(err error) error {
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return w.p.closeWrite(err)
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}
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// Pipe creates a synchronous in-memory pipe.
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// It can be used to connect code expecting an io.Reader
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// with code expecting an io.Writer.
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//
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// Reads and Writes on the pipe are matched one to one
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// except when multiple Reads are needed to consume a single Write.
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// That is, each Write to the PipeWriter blocks until it has satisfied
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// one or more Reads from the PipeReader that fully consume
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// the written data.
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// The data is copied directly from the Write to the corresponding
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// Read (or Reads); there is no internal buffering.
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//
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// It is safe to call Read and Write in parallel with each other or with Close.
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// Parallel calls to Read and parallel calls to Write are also safe:
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// the individual calls will be gated sequentially.
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func Pipe() (*PipeReader, *PipeWriter) {
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p := &pipe{
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wrCh: make(chan []byte),
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rdCh: make(chan int),
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done: make(chan struct{}),
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}
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return &PipeReader{p}, &PipeWriter{p}
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}
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