lib/readers: add NoCloser to stop upgrades from io.Reader to io.ReadCloser

lib/readers/noclose.go

@@ -0,0 +1,29 @@
+package readers
+
+import "io"
+
+// noClose is used to wrap an io.Reader to stop it being upgraded
+type noClose struct {
+	in io.Reader
+}
+
+// Read implements io.Closer by passing it straight on
+func (nc noClose) Read(p []byte) (n int, err error) {
+	return nc.in.Read(p)
+}
+
+// NoCloser makes sure that the io.Reader passed in can't upgraded to
+// an io.Closer.
+//
+// This is for use with http.NewRequest to make sure the body doesn't
+// get upgraded to an io.Closer and the body closed unexpectedly.
+func NoCloser(in io.Reader) io.Reader {
+	if in == nil {
+		return in
+	}
+	// if in doesn't implement io.Closer, just return it
+	if _, canClose := in.(io.Closer); !canClose {
+		return in
+	}
+	return noClose{in: in}
+}

lib/readers/noclose_test.go

@@ -0,0 +1,44 @@
+package readers
+
+import (
+	"io"
+	"testing"
+
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/assert"
+)
+
+var errRead = errors.New("read error")
+
+type readOnly struct{}
+
+func (readOnly) Read(p []byte) (n int, err error) {
+	return 0, io.EOF
+}
+
+type readClose struct{}
+
+func (readClose) Read(p []byte) (n int, err error) {
+	return 0, errRead
+}
+
+func (readClose) Close() (err error) {
+	return io.EOF
+}
+
+func TestNoCloser(t *testing.T) {
+	assert.Equal(t, nil, NoCloser(nil))
+
+	ro := readOnly{}
+	assert.Equal(t, ro, NoCloser(ro))
+
+	rc := readClose{}
+	nc := NoCloser(rc)
+	assert.NotEqual(t, nc, rc)
+
+	_, hasClose := nc.(io.Closer)
+	assert.False(t, hasClose)
+
+	_, err := nc.Read(nil)
+	assert.Equal(t, errRead, err)
+}