make the buffered qlog writer used in interop flush before closing

example/client/main.go

@@ -62,13 +62,7 @@ func main() {
 				log.Fatal(err)
 			}
 			log.Printf("Creating qlog file %s.\n", filename)
-			return struct {
-				io.Writer
-				io.Closer
-			}{
-				bufio.NewWriter(f),
-				f,
-			}
+			return utils.NewBufferedWriteCloser(bufio.NewWriter(f), f)
 		}
 	}
 	roundTripper := &http3.RoundTripper{

example/main.go

@@ -216,13 +216,7 @@ func main() {
 				log.Fatal(err)
 			}
 			log.Printf("Creating qlog file %s.\n", filename)
-			return struct {
-				io.Writer
-				io.Closer
-			}{
-				bufio.NewWriter(f),
-				f,
-			}
+			return utils.NewBufferedWriteCloser(bufio.NewWriter(f), f)
 		}
 	}
 

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"))
+	})
+})

interop/utils/logging.go

@@ -7,6 +7,8 @@ import (
 	"log"
 	"os"
 	"strings"
+
+	"github.com/lucas-clemente/quic-go/internal/utils"
 )
 
 // GetSSLKeyLog creates a file for the TLS key log
@@ -39,12 +41,6 @@ func GetQLOGWriter() (func(connID []byte) io.WriteCloser, error) {
 		if err != nil {
 			log.Fatalf("Failed to create qlog file %s: %s", path, err.Error())
 		}
-		return struct {
-			io.Writer
-			io.Closer
-		}{
-			bufio.NewWriter(f),
-			f,
-		}
+		return utils.NewBufferedWriteCloser(bufio.NewWriter(f), f)
 	}, nil
 }