Imported Upstream version 1.4upstream/1.4

1 files changed, 193 insertions, 0 deletions

diff --git a/src/io/pipe.go b/src/io/pipe.go
new file mode 100644
index 000000000..f65354a7f
--- /dev/null
+++ b/src/io/pipe.go
@@ -0,0 +1,193 @@
+// 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"
+)
+
+// ErrClosedPipe is the error used for read or write operations on a closed pipe.
+var ErrClosedPipe = errors.New("io: read/write on closed pipe")
+
+type pipeResult struct {
+	n   int
+	err error
+}
+
+// A pipe is the shared pipe structure underlying PipeReader and PipeWriter.
+type pipe struct {
+	rl    sync.Mutex // gates readers one at a time
+	wl    sync.Mutex // gates writers one at a time
+	l     sync.Mutex // protects remaining fields
+	data  []byte     // data remaining in pending write
+	rwait sync.Cond  // waiting reader
+	wwait sync.Cond  // waiting writer
+	rerr  error      // if reader closed, error to give writes
+	werr  error      // if writer closed, error to give reads
+}
+
+func (p *pipe) read(b []byte) (n int, err error) {
+	// One reader at a time.
+	p.rl.Lock()
+	defer p.rl.Unlock()
+
+	p.l.Lock()
+	defer p.l.Unlock()
+	for {
+		if p.rerr != nil {
+			return 0, ErrClosedPipe
+		}
+		if p.data != nil {
+			break
+		}
+		if p.werr != nil {
+			return 0, p.werr
+		}
+		p.rwait.Wait()
+	}
+	n = copy(b, p.data)
+	p.data = p.data[n:]
+	if len(p.data) == 0 {
+		p.data = nil
+		p.wwait.Signal()
+	}
+	return
+}
+
+var zero [0]byte
+
+func (p *pipe) write(b []byte) (n int, err error) {
+	// pipe uses nil to mean not available
+	if b == nil {
+		b = zero[:]
+	}
+
+	// One writer at a time.
+	p.wl.Lock()
+	defer p.wl.Unlock()
+
+	p.l.Lock()
+	defer p.l.Unlock()
+	if p.werr != nil {
+		err = ErrClosedPipe
+		return
+	}
+	p.data = b
+	p.rwait.Signal()
+	for {
+		if p.data == nil {
+			break
+		}
+		if p.rerr != nil {
+			err = p.rerr
+			break
+		}
+		if p.werr != nil {
+			err = ErrClosedPipe
+		}
+		p.wwait.Wait()
+	}
+	n = len(b) - len(p.data)
+	p.data = nil // in case of rerr or werr
+	return
+}
+
+func (p *pipe) rclose(err error) {
+	if err == nil {
+		err = ErrClosedPipe
+	}
+	p.l.Lock()
+	defer p.l.Unlock()
+	p.rerr = err
+	p.rwait.Signal()
+	p.wwait.Signal()
+}
+
+func (p *pipe) wclose(err error) {
+	if err == nil {
+		err = EOF
+	}
+	p.l.Lock()
+	defer p.l.Unlock()
+	p.werr = err
+	p.rwait.Signal()
+	p.wwait.Signal()
+}
+
+// A PipeReader is the read half of a pipe.
+type PipeReader struct {
+	p *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.p.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.
+func (r *PipeReader) CloseWithError(err error) error {
+	r.p.rclose(err)
+	return nil
+}
+
+// A PipeWriter is the write half of a pipe.
+type PipeWriter struct {
+	p *pipe
+}
+
+// Write implements the standard Write interface:
+// it writes data to the pipe, blocking until 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.p.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.
+func (w *PipeWriter) CloseWithError(err error) error {
+	w.p.wclose(err)
+	return nil
+}
+
+// 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 on one end are matched with writes on the other,
+// copying data directly between the two; there is no internal buffering.
+// It is safe to call Read and Write in parallel with each other or with
+// Close. Close will complete once pending I/O is done. Parallel calls to
+// Read, and parallel calls to Write, are also safe:
+// the individual calls will be gated sequentially.
+func Pipe() (*PipeReader, *PipeWriter) {
+	p := new(pipe)
+	p.rwait.L = &p.l
+	p.wwait.L = &p.l
+	r := &PipeReader{p}
+	w := &PipeWriter{p}
+	return r, w
+}