move some io related utils to pkg/ioutils

Docker-DCO-1.1-Signed-off-by: Cristian Staretu <cristian.staretu@gmail.com> (github: unclejack)

ioutils/readers.go

@@ -0,0 +1,82 @@
+package ioutils
+
+import (
+	"bytes"
+	"io"
+	"sync"
+)
+
+type readCloserWrapper struct {
+	io.Reader
+	closer func() error
+}
+
+func (r *readCloserWrapper) Close() error {
+	return r.closer()
+}
+
+func NewReadCloserWrapper(r io.Reader, closer func() error) io.ReadCloser {
+	return &readCloserWrapper{
+		Reader: r,
+		closer: closer,
+	}
+}
+
+type bufReader struct {
+	sync.Mutex
+	buf    *bytes.Buffer
+	reader io.Reader
+	err    error
+	wait   sync.Cond
+}
+
+func NewBufReader(r io.Reader) *bufReader {
+	reader := &bufReader{
+		buf:    &bytes.Buffer{},
+		reader: r,
+	}
+	reader.wait.L = &reader.Mutex
+	go reader.drain()
+	return reader
+}
+
+func (r *bufReader) drain() {
+	buf := make([]byte, 1024)
+	for {
+		n, err := r.reader.Read(buf)
+		r.Lock()
+		if err != nil {
+			r.err = err
+		} else {
+			r.buf.Write(buf[0:n])
+		}
+		r.wait.Signal()
+		r.Unlock()
+		if err != nil {
+			break
+		}
+	}
+}
+
+func (r *bufReader) Read(p []byte) (n int, err error) {
+	r.Lock()
+	defer r.Unlock()
+	for {
+		n, err = r.buf.Read(p)
+		if n > 0 {
+			return n, err
+		}
+		if r.err != nil {
+			return 0, r.err
+		}
+		r.wait.Wait()
+	}
+}
+
+func (r *bufReader) Close() error {
+	closer, ok := r.reader.(io.ReadCloser)
+	if !ok {
+		return nil
+	}
+	return closer.Close()
+}

ioutils/readers_test.go

@@ -0,0 +1,34 @@
+package ioutils
+
+import (
+	"bytes"
+	"io"
+	"io/ioutil"
+	"testing"
+)
+
+func TestBufReader(t *testing.T) {
+	reader, writer := io.Pipe()
+	bufreader := NewBufReader(reader)
+
+	// Write everything down to a Pipe
+	// Usually, a pipe should block but because of the buffered reader,
+	// the writes will go through
+	done := make(chan bool)
+	go func() {
+		writer.Write([]byte("hello world"))
+		writer.Close()
+		done <- true
+	}()
+
+	// Drain the reader *after* everything has been written, just to verify
+	// it is indeed buffering
+	<-done
+	output, err := ioutil.ReadAll(bufreader)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(output, []byte("hello world")) {
+		t.Error(string(output))
+	}
+}

ioutils/writers.go

@@ -0,0 +1,23 @@
+package ioutils
+
+import "io"
+
+type NopWriter struct{}
+
+func (*NopWriter) Write(buf []byte) (int, error) {
+	return len(buf), nil
+}
+
+type nopWriteCloser struct {
+	io.Writer
+}
+
+func (w *nopWriteCloser) Close() error { return nil }
+
+func NopWriteCloser(w io.Writer) io.WriteCloser {
+	return &nopWriteCloser{w}
+}
+
+type NopFlusher struct{}
+
+func (f *NopFlusher) Flush() {}