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129 lines
3.4 KiB
129 lines
3.4 KiB
package bufpipe
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import (
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"bytes"
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"errors"
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"io"
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"sync"
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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("bufpipe: read/write on closed pipe")
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type pipe struct {
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cond *sync.Cond
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buf *bytes.Buffer
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rerr, werr error
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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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*pipe
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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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*pipe
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}
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// New creates a synchronous pipe using buf as its initial contents. It can be
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// used to connect code expecting an io.Reader with code expecting an io.Writer.
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//
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// Unlike io.Pipe, writes never block because the internal buffer has variable
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// size. Reads block only when the buffer is empty.
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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: the
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// individual calls will be gated sequentially.
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//
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// The new pipe takes ownership of buf, and the caller should not use buf after
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// this call. New is intended to prepare a PipeReader to read existing data. It
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// can also be used to set the initial size of the internal buffer for writing.
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// To do that, buf should have the desired capacity but a length of zero.
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func New(buf []byte) (*PipeReader, *PipeWriter) {
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p := &pipe{
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buf: bytes.NewBuffer(buf),
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cond: sync.NewCond(new(sync.Mutex)),
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}
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return &PipeReader{
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pipe: p,
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}, &PipeWriter{
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pipe: p,
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}
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}
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// Read implements the standard Read interface: it reads data from the pipe,
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// reading from the internal buffer, otherwise blocking until a writer arrives
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// or the write end is closed. If the write end is closed with an error, that
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// error is returned as err; otherwise err is io.EOF.
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func (r *PipeReader) Read(data []byte) (int, error) {
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r.cond.L.Lock()
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defer r.cond.L.Unlock()
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RETRY:
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n, err := r.buf.Read(data)
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// If not closed and no read, wait for writing.
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if err == io.EOF && r.rerr == nil && n == 0 {
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r.cond.Wait()
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goto RETRY
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}
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if err == io.EOF {
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return n, r.rerr
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}
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return n, err
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}
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// Close closes the reader; subsequent writes from the write half of the pipe
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// will return 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 to the write half of the
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// pipe will return the error err.
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func (r *PipeReader) CloseWithError(err error) error {
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r.cond.L.Lock()
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defer r.cond.L.Unlock()
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if err == nil {
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err = ErrClosedPipe
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}
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r.werr = err
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return nil
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}
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// Write implements the standard Write interface: it writes data to the internal
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// buffer. If the read end is closed with an error, that err is returned as err;
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// otherwise err is ErrClosedPipe.
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func (w *PipeWriter) Write(data []byte) (int, error) {
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w.cond.L.Lock()
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defer w.cond.L.Unlock()
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if w.werr != nil {
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return 0, w.werr
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}
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n, err := w.buf.Write(data)
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w.cond.Signal()
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return n, err
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}
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// Close closes the writer; subsequent reads from the read half of the pipe will
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// return io.EOF once the internal buffer get empty.
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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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// Close closes the writer; subsequent reads from the read half of the pipe will
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// return err once the internal buffer get empty.
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func (w *PipeWriter) CloseWithError(err error) error {
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w.cond.L.Lock()
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defer w.cond.L.Unlock()
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if err == nil {
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err = io.EOF
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}
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w.rerr = err
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return nil
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}
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