Add FillReader and DevZero

fill.go

@@ -0,0 +1,21 @@
+package plumbing
+
+import "io"
+
+type fillReader struct {
+	b byte
+}
+
+func (r *fillReader) Read(p []byte) (int, error) {
+	for i := range p {
+		p[i] = r.b
+	}
+
+	return len(p), nil
+}
+
+// FillReader returns an io.Reader such that Read calls return an unlimited
+// stream of b bytes.
+func FillReader(b byte) io.Reader {
+	return &fillReader{b}
+}

zero.go

@@ -0,0 +1,18 @@
+package plumbing
+
+import "io"
+
+type devZero struct {
+	io.Reader
+}
+
+func (w *devZero) Write(p []byte) (int, error) {
+	return len(p), nil
+}
+
+// DevZero returns an io.ReadWriter that behaves like /dev/zero such that Read
+// calls return an unlimited stream of zero bytes and all Write calls succeed
+// without doing anything.
+func DevZero() io.ReadWriter {
+	return &devZero{FillReader(0)}
+}

zero_test.go

@@ -0,0 +1,36 @@
+package plumbing_test
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/bodgit/plumbing"
+	"github.com/stretchr/testify/assert"
+)
+
+const limit = 10
+
+func TestDevZero(t *testing.T) {
+	t.Parallel()
+
+	rw := plumbing.DevZero()
+	b := new(bytes.Buffer)
+
+	n, err := io.Copy(b, io.LimitReader(rw, limit))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, limit, int(n))
+	assert.Equal(t, limit, b.Len())
+	assert.Equal(t, bytes.Repeat([]byte{0x00}, limit), b.Bytes())
+
+	n, err = io.Copy(rw, b)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, limit, int(n))
+	assert.Equal(t, 0, b.Len())
+}