TUN-6679: Allow client side of quic request to close body

In a previous commit, we fixed a bug where the client roundtrip code
could close the request body, which in fact would be the quic.Stream,
thus closing the write-side.
The way that was fixed, prevented the client roundtrip code from closing
also read-side (the body).

This fixes that, by allowing close to only close the read side, which
will guarantee that any subsquent will fail with an error or EOF it
occurred before the close.

connection/quic_test.go

@@ -10,6 +10,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -527,6 +528,44 @@ func TestServeUDPSession(t *testing.T) {
 	cancel()
 }
 
+func TestNopCloserReadWriterCloseBeforeEOF(t *testing.T) {
+	readerWriter := nopCloserReadWriter{ReadWriteCloser: &mockReaderNoopWriter{Reader: strings.NewReader("123456789")}}
+	buffer := make([]byte, 5)
+
+	n, err := readerWriter.Read(buffer)
+	require.NoError(t, err)
+	require.Equal(t, n, 5)
+
+	// close
+	require.NoError(t, readerWriter.Close())
+
+	// read should get error
+	n, err = readerWriter.Read(buffer)
+	require.Equal(t, n, 0)
+	require.Equal(t, err, fmt.Errorf("closed by handler"))
+}
+
+func TestNopCloserReadWriterCloseAfterEOF(t *testing.T) {
+	readerWriter := nopCloserReadWriter{ReadWriteCloser: &mockReaderNoopWriter{Reader: strings.NewReader("123456789")}}
+	buffer := make([]byte, 20)
+
+	n, err := readerWriter.Read(buffer)
+	require.NoError(t, err)
+	require.Equal(t, n, 9)
+
+	// force another read to read eof
+	n, err = readerWriter.Read(buffer)
+	require.Equal(t, err, io.EOF)
+
+	// close
+	require.NoError(t, readerWriter.Close())
+
+	// read should get EOF still
+	n, err = readerWriter.Read(buffer)
+	require.Equal(t, n, 0)
+	require.Equal(t, err, io.EOF)
+}
+
 func serveSession(ctx context.Context, qc *QUICConnection, edgeQUICSession quic.Connection, closeType closeReason, expectedReason string, t *testing.T) {
 	var (
 		payload = []byte(t.Name())
@@ -647,3 +686,15 @@ func testQUICConnection(udpListenerAddr net.Addr, t *testing.T) *QUICConnection
 	require.NoError(t, err)
 	return qc
 }
+
+type mockReaderNoopWriter struct {
+	io.Reader
+}
+
+func (m *mockReaderNoopWriter) Write(p []byte) (n int, err error) {
+	return len(p), nil
+}
+
+func (m *mockReaderNoopWriter) Close() error {
+	return nil
+}