Write overflow - test validating truncated writes

channel_test.go

@@ -0,0 +1,78 @@
+package p9p
+
+import (
+	"bytes"
+	"context"
+	"encoding/binary"
+	"errors"
+	"net"
+	"testing"
+	"time"
+)
+
+type fakeAddr struct{}
+
+func (a fakeAddr) Network() string {
+	return ""
+}
+func (a fakeAddr) String() string {
+	return "fake address"
+}
+
+type writeConnMock struct {
+	data []byte
+}
+
+func (c *writeConnMock) Read(b []byte) (n int, err error) {
+	return 0, errors.New("not implemented")
+}
+
+func (c *writeConnMock) Write(b []byte) (n int, err error) {
+	c.data = append(c.data, b...)
+
+	n = len(b)
+	return n, nil
+}
+
+func (c *writeConnMock) Close() error {
+	return nil
+}
+
+func (c *writeConnMock) LocalAddr() net.Addr {
+	return fakeAddr{}
+}
+
+func (c *writeConnMock) RemoteAddr() net.Addr {
+	return fakeAddr{}
+}
+
+func (c *writeConnMock) SetDeadline(t time.Time) error {
+	return nil
+}
+
+func (c *writeConnMock) SetReadDeadline(t time.Time) error {
+	return nil
+}
+
+func (c *writeConnMock) SetWriteDeadline(t time.Time) error {
+	return nil
+}
+
+func TestWriteOverflow(t *testing.T) {
+	const testMsize = 500
+	conn := writeConnMock{}
+	channel := newChannel(&conn, NewCodec(), testMsize)
+	writeRequest := MessageTwrite{1, 0, make([]byte, 2*testMsize)}
+	ctx := context.Background()
+	channel.WriteFcall(ctx, newFcall(Tag(1), writeRequest))
+	reader := bytes.NewReader(conn.data)
+	var writtenSize uint32
+	err := binary.Read(reader, binary.LittleEndian, &writtenSize)
+	if err != nil {
+		t.Errorf("error reading result: %v", err)
+	}
+	// as there is an overflow, written size should have been truncated such that the message size is equal to channel's msize
+	if int(writtenSize) != testMsize {
+		t.Errorf("message should have been truncated to size %v. written message has size %v", testMsize, writtenSize)
+	}
+}