make the buffered qlog writer used in interop flush before closing

internal/utils/buffered_write_closer.go

@@ -0,0 +1,26 @@
+package utils
+
+import (
+	"bufio"
+	"io"
+)
+
+type bufferedWriteCloser struct {
+	*bufio.Writer
+	io.Closer
+}
+
+// NewBufferedWriteCloser creates an io.WriteCloser from a bufio.Writer and an io.Closer
+func NewBufferedWriteCloser(writer *bufio.Writer, closer io.Closer) io.WriteCloser {
+	return &bufferedWriteCloser{
+		Writer: writer,
+		Closer: closer,
+	}
+}
+
+func (h bufferedWriteCloser) Close() error {
+	if err := h.Writer.Flush(); err != nil {
+		return err
+	}
+	return h.Closer.Close()
+}

internal/utils/buffered_write_closer_test.go

@@ -0,0 +1,26 @@
+package utils
+
+import (
+	"bufio"
+	"bytes"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+type nopCloser struct{}
+
+func (nopCloser) Close() error { return nil }
+
+var _ = Describe("buffered io.WriteCloser", func() {
+	It("flushes before closing", func() {
+		buf := &bytes.Buffer{}
+
+		w := bufio.NewWriter(buf)
+		wc := NewBufferedWriteCloser(w, &nopCloser{})
+		wc.Write([]byte("foobar"))
+		Expect(buf.Len()).To(BeZero())
+		Expect(wc.Close()).To(Succeed())
+		Expect(buf.String()).To(Equal("foobar"))
+	})
+})