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