Handle errcheck warnings

The package ignored errors from net.Conn Set*Deadline in a few places.
Update the package to return these errors to the caller.

Ignore all other errors reported by errcheck. These errors are safe to
ignore because
- The function is making a best effort to cleanup while handling another
  error.
- The function call is guaranteed to succeed.
- The error is ignored in a test.

client.go

@@ -328,9 +328,15 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 		})
 	}
 
+	// Close the network connection when returning an error. The variable
+	// netConn is set to nil before the success return at the end of the
+	// function.
 	defer func() {
 		if netConn != nil {
-			netConn.Close()
+			// It's safe to ignore the error from Close() because this code is
+			// only executed when returning a more important error to the
+			// application.
+			_ = netConn.Close()
 		}
 	}()
 
@@ -421,8 +427,14 @@ func (d *Dialer) DialContext(ctx context.Context, urlStr string, requestHeader h
 	resp.Body = ioutil.NopCloser(bytes.NewReader([]byte{}))
 	conn.subprotocol = resp.Header.Get("Sec-Websocket-Protocol")
 
-	netConn.SetDeadline(time.Time{})
+	if err := netConn.SetDeadline(time.Time{}); err != nil {
-	netConn = nil // to avoid close in defer.
+		return nil, resp, err
+	}
+
+	// Success! Set netConn to nil to stop the deferred function above from
+	// closing the network connection.
+	netConn = nil
+
 	return conn, resp, nil
 }
 

client_server_test.go

@@ -531,7 +531,7 @@ func TestRespOnBadHandshake(t *testing.T) {
 
 	s := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(expectedStatus)
-		io.WriteString(w, expectedBody)
+		_, _ = io.WriteString(w, expectedBody)
 	}))
 	defer s.Close()
 
@@ -781,7 +781,7 @@ func TestSocksProxyDial(t *testing.T) {
 		}
 		defer c1.Close()
 
-		c1.SetDeadline(time.Now().Add(30 * time.Second))
+		_ = c1.SetDeadline(time.Now().Add(30 * time.Second))
 
 		buf := make([]byte, 32)
 		if _, err := io.ReadFull(c1, buf[:3]); err != nil {
@@ -820,10 +820,10 @@ func TestSocksProxyDial(t *testing.T) {
 		defer c2.Close()
 		done := make(chan struct{})
 		go func() {
-			io.Copy(c1, c2)
+			_, _ = io.Copy(c1, c2)
 			close(done)
 		}()
-		io.Copy(c2, c1)
+		_, _ = io.Copy(c2, c1)
 		<-done
 	}()
 

compression.go

@@ -33,7 +33,11 @@ func decompressNoContextTakeover(r io.Reader) io.ReadCloser {
 		"\x01\x00\x00\xff\xff"
 
 	fr, _ := flateReaderPool.Get().(io.ReadCloser)
-	fr.(flate.Resetter).Reset(io.MultiReader(r, strings.NewReader(tail)), nil)
+	mr := io.MultiReader(r, strings.NewReader(tail))
+	if err := fr.(flate.Resetter).Reset(mr, nil); err != nil {
+		// Reset never fails, but handle error in case that changes.
+		fr = flate.NewReader(mr)
+	}
 	return &flateReadWrapper{fr}
 }
 

compression_test.go

@@ -23,7 +23,7 @@ func TestTruncWriter(t *testing.T) {
 			if m > n {
 				m = n
 			}
-			w.Write(p[:m])
+			_, _ = w.Write(p[:m])
 			p = p[m:]
 		}
 		if b.String() != data[:len(data)-len(w.p)] {
@@ -47,7 +47,7 @@ func BenchmarkWriteNoCompression(b *testing.B) {
 	messages := textMessages(100)
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		c.WriteMessage(TextMessage, messages[i%len(messages)])
+		_ = c.WriteMessage(TextMessage, messages[i%len(messages)])
 	}
 	b.ReportAllocs()
 }
@@ -60,7 +60,7 @@ func BenchmarkWriteWithCompression(b *testing.B) {
 	c.newCompressionWriter = compressNoContextTakeover
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		c.WriteMessage(TextMessage, messages[i%len(messages)])
+		_ = c.WriteMessage(TextMessage, messages[i%len(messages)])
 	}
 	b.ReportAllocs()
 }

conn.go

@@ -372,7 +372,9 @@ func (c *Conn) read(n int) ([]byte, error) {
 	if err == io.EOF {
 		err = errUnexpectedEOF
 	}
-	c.br.Discard(len(p))
+	// Discard is guaranteed to succeed because the number of bytes to discard
+	// is less than or equal to the number of bytes buffered.
+	_, _ = c.br.Discard(len(p))
 	return p, err
 }
 
@@ -387,7 +389,9 @@ func (c *Conn) write(frameType int, deadline time.Time, buf0, buf1 []byte) error
 		return err
 	}
 
-	c.conn.SetWriteDeadline(deadline)
+	if err := c.conn.SetWriteDeadline(deadline); err != nil {
+		return c.writeFatal(err)
+	}
 	if len(buf1) == 0 {
 		_, err = c.conn.Write(buf0)
 	} else {
@@ -397,7 +401,7 @@ func (c *Conn) write(frameType int, deadline time.Time, buf0, buf1 []byte) error
 		return c.writeFatal(err)
 	}
 	if frameType == CloseMessage {
-		c.writeFatal(ErrCloseSent)
+		_ = c.writeFatal(ErrCloseSent)
 	}
 	return nil
 }
@@ -460,13 +464,14 @@ func (c *Conn) WriteControl(messageType int, data []byte, deadline time.Time) er
 		return err
 	}
 
-	c.conn.SetWriteDeadline(deadline)
+	if err := c.conn.SetWriteDeadline(deadline); err != nil {
-	_, err = c.conn.Write(buf)
+		return c.writeFatal(err)
-	if err != nil {
+	}
+	if _, err = c.conn.Write(buf); err != nil {
 		return c.writeFatal(err)
 	}
 	if messageType == CloseMessage {
-		c.writeFatal(ErrCloseSent)
+		_ = c.writeFatal(ErrCloseSent)
 	}
 	return err
 }
@@ -630,7 +635,7 @@ func (w *messageWriter) flushFrame(final bool, extra []byte) error {
 	}
 
 	if final {
-		w.endMessage(errWriteClosed)
+		_ = w.endMessage(errWriteClosed)
 		return nil
 	}
 
@@ -817,7 +822,7 @@ func (c *Conn) advanceFrame() (int, error) {
 	rsv2 := p[0]&rsv2Bit != 0
 	rsv3 := p[0]&rsv3Bit != 0
 	mask := p[1]&maskBit != 0
-	c.setReadRemaining(int64(p[1] & 0x7f))
+	_ = c.setReadRemaining(int64(p[1] & 0x7f)) // will not fail because argument is >= 0
 
 	c.readDecompress = false
 	if rsv1 {
@@ -922,7 +927,8 @@ func (c *Conn) advanceFrame() (int, error) {
 		}
 
 		if c.readLimit > 0 && c.readLength > c.readLimit {
-			c.WriteControl(CloseMessage, FormatCloseMessage(CloseMessageTooBig, ""), time.Now().Add(writeWait))
+			// Make a best effort to send a close message describing the problem.
+			_ = c.WriteControl(CloseMessage, FormatCloseMessage(CloseMessageTooBig, ""), time.Now().Add(writeWait))
 			return noFrame, ErrReadLimit
 		}
 
@@ -934,7 +940,7 @@ func (c *Conn) advanceFrame() (int, error) {
 	var payload []byte
 	if c.readRemaining > 0 {
 		payload, err = c.read(int(c.readRemaining))
-		c.setReadRemaining(0)
+		_ = c.setReadRemaining(0) // will not fail because argument is >= 0
 		if err != nil {
 			return noFrame, err
 		}
@@ -981,7 +987,8 @@ func (c *Conn) handleProtocolError(message string) error {
 	if len(data) > maxControlFramePayloadSize {
 		data = data[:maxControlFramePayloadSize]
 	}
-	c.WriteControl(CloseMessage, data, time.Now().Add(writeWait))
+	// Make a best effor to send a close message describing the problem.
+	_ = c.WriteControl(CloseMessage, data, time.Now().Add(writeWait))
 	return errors.New("websocket: " + message)
 }
 
@@ -1054,7 +1061,7 @@ func (r *messageReader) Read(b []byte) (int, error) {
 			}
 			rem := c.readRemaining
 			rem -= int64(n)
-			c.setReadRemaining(rem)
+			_ = c.setReadRemaining(rem) // rem is guaranteed to be >= 0
 			if c.readRemaining > 0 && c.readErr == io.EOF {
 				c.readErr = errUnexpectedEOF
 			}
@@ -1136,7 +1143,8 @@ func (c *Conn) SetCloseHandler(h func(code int, text string) error) {
 	if h == nil {
 		h = func(code int, text string) error {
 			message := FormatCloseMessage(code, "")
-			c.WriteControl(CloseMessage, message, time.Now().Add(writeWait))
+			// Make a best effor to send the close message.
+			_ = c.WriteControl(CloseMessage, message, time.Now().Add(writeWait))
 			return nil
 		}
 	}

conn_broadcast_test.go

@@ -70,9 +70,9 @@ func (b *broadcastBench) makeConns(numConns int) {
 				select {
 				case msg := <-c.msgCh:
 					if msg.prepared != nil {
-						c.conn.WritePreparedMessage(msg.prepared)
+						_ = c.conn.WritePreparedMessage(msg.prepared)
 					} else {
-						c.conn.WriteMessage(TextMessage, msg.payload)
+						_ = c.conn.WriteMessage(TextMessage, msg.payload)
 					}
 					val := atomic.AddInt32(&b.count, 1)
 					if val%int32(numConns) == 0 {

conn_test.go

@@ -158,7 +158,7 @@ func TestControl(t *testing.T) {
 			wc := newTestConn(nil, &connBuf, isServer)
 			rc := newTestConn(&connBuf, nil, !isServer)
 			if isWriteControl {
-				wc.WriteControl(PongMessage, []byte(message), time.Now().Add(time.Second))
+				_ = wc.WriteControl(PongMessage, []byte(message), time.Now().Add(time.Second))
 			} else {
 				w, err := wc.NextWriter(PongMessage)
 				if err != nil {
@@ -175,7 +175,7 @@ func TestControl(t *testing.T) {
 				}
 				var actualMessage string
 				rc.SetPongHandler(func(s string) error { actualMessage = s; return nil })
-				rc.NextReader()
+				_, _, _ = rc.NextReader()
 				if actualMessage != message {
 					t.Errorf("%s: pong=%q, want %q", name, actualMessage, message)
 					continue
@@ -359,8 +359,8 @@ func TestCloseFrameBeforeFinalMessageFrame(t *testing.T) {
 	rc := newTestConn(&b1, &b2, true)
 
 	w, _ := wc.NextWriter(BinaryMessage)
-	w.Write(make([]byte, bufSize+bufSize/2))
+	_, _ = w.Write(make([]byte, bufSize+bufSize/2))
-	wc.WriteControl(CloseMessage, FormatCloseMessage(expectedErr.Code, expectedErr.Text), time.Now().Add(10*time.Second))
+	_ = wc.WriteControl(CloseMessage, FormatCloseMessage(expectedErr.Code, expectedErr.Text), time.Now().Add(10*time.Second))
 	w.Close()
 
 	op, r, err := rc.NextReader()
@@ -386,7 +386,7 @@ func TestEOFWithinFrame(t *testing.T) {
 		rc := newTestConn(&b, nil, true)
 
 		w, _ := wc.NextWriter(BinaryMessage)
-		w.Write(make([]byte, bufSize))
+		_, _ = w.Write(make([]byte, bufSize))
 		w.Close()
 
 		if n >= b.Len() {
@@ -420,7 +420,7 @@ func TestEOFBeforeFinalFrame(t *testing.T) {
 	rc := newTestConn(&b1, &b2, true)
 
 	w, _ := wc.NextWriter(BinaryMessage)
-	w.Write(make([]byte, bufSize+bufSize/2))
+	_, _ = w.Write(make([]byte, bufSize+bufSize/2))
 
 	op, r, err := rc.NextReader()
 	if op != BinaryMessage || err != nil {
@@ -439,7 +439,7 @@ func TestEOFBeforeFinalFrame(t *testing.T) {
 func TestWriteAfterMessageWriterClose(t *testing.T) {
 	wc := newTestConn(nil, &bytes.Buffer{}, false)
 	w, _ := wc.NextWriter(BinaryMessage)
-	io.WriteString(w, "hello")
+	_, _ = io.WriteString(w, "hello")
 	if err := w.Close(); err != nil {
 		t.Fatalf("unxpected error closing message writer, %v", err)
 	}
@@ -449,7 +449,7 @@ func TestWriteAfterMessageWriterClose(t *testing.T) {
 	}
 
 	w, _ = wc.NextWriter(BinaryMessage)
-	io.WriteString(w, "hello")
+	_, _ = io.WriteString(w, "hello")
 
 	// close w by getting next writer
 	_, err := wc.NextWriter(BinaryMessage)
@@ -474,13 +474,13 @@ func TestReadLimit(t *testing.T) {
 
 		// Send message at the limit with interleaved pong.
 		w, _ := wc.NextWriter(BinaryMessage)
-		w.Write(message[:readLimit-1])
+		_, _ = w.Write(message[:readLimit-1])
-		wc.WriteControl(PongMessage, []byte("this is a pong"), time.Now().Add(10*time.Second))
+		_ = wc.WriteControl(PongMessage, []byte("this is a pong"), time.Now().Add(10*time.Second))
-		w.Write(message[:1])
+		_, _ = w.Write(message[:1])
 		w.Close()
 
 		// Send message larger than the limit.
-		wc.WriteMessage(BinaryMessage, message[:readLimit+1])
+		_ = wc.WriteMessage(BinaryMessage, message[:readLimit+1])
 
 		op, _, err := rc.NextReader()
 		if op != BinaryMessage || err != nil {
@@ -593,7 +593,7 @@ func TestBufioReadBytes(t *testing.T) {
 	rc := newConn(fakeNetConn{Reader: &b1, Writer: &b2}, true, len(m)-64, len(m)-64, nil, nil, nil)
 
 	w, _ := wc.NextWriter(BinaryMessage)
-	w.Write(m)
+	_, _ = w.Write(m)
 	w.Close()
 
 	op, r, err := rc.NextReader()
@@ -667,7 +667,7 @@ func TestConcurrentWritePanic(t *testing.T) {
 	w := blockingWriter{make(chan struct{}), make(chan struct{})}
 	c := newTestConn(nil, w, false)
 	go func() {
-		c.WriteMessage(TextMessage, []byte{})
+		_ = c.WriteMessage(TextMessage, []byte{})
 	}()
 
 	// wait for goroutine to block in write.
@@ -680,7 +680,7 @@ func TestConcurrentWritePanic(t *testing.T) {
 		}
 	}()
 
-	c.WriteMessage(TextMessage, []byte{})
+	_ = c.WriteMessage(TextMessage, []byte{})
 	t.Fatal("should not get here")
 }
 
@@ -700,7 +700,7 @@ func TestFailedConnectionReadPanic(t *testing.T) {
 	}()
 
 	for i := 0; i < 20000; i++ {
-		c.ReadMessage()
+		_, _, _ = c.ReadMessage()
 	}
 	t.Fatal("should not get here")
 }

join_test.go

@@ -19,7 +19,7 @@ func TestJoinMessages(t *testing.T) {
 			wc := newTestConn(nil, &connBuf, true)
 			rc := newTestConn(&connBuf, nil, false)
 			for _, m := range messages {
-				wc.WriteMessage(BinaryMessage, []byte(m))
+				_ = wc.WriteMessage(BinaryMessage, []byte(m))
 			}
 
 			var result bytes.Buffer

prepared_test.go

@@ -40,7 +40,9 @@ func TestPreparedMessage(t *testing.T) {
 		if tt.enableWriteCompression {
 			c.newCompressionWriter = compressNoContextTakeover
 		}
-		c.SetCompressionLevel(tt.compressionLevel)
+		if err := c.SetCompressionLevel(tt.compressionLevel); err != nil {
+			t.Fatal(err)
+		}
 
 		// Seed random number generator for consistent frame mask.
 		rand.Seed(1234)

server.go

@@ -182,8 +182,19 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 		return u.returnError(w, r, http.StatusInternalServerError, err.Error())
 	}
 
+	// Close the network connection when returning an error. The variable
+	// netConn is set to nil before the success return at the end of the
+	// function.
+	defer func() {
+		if netConn != nil {
+			// It's safe to ignore the error from Close() because this code is
+			// only executed when returning a more important error to the
+			// application.
+			_ = netConn.Close()
+		}
+	}()
+
 	if brw.Reader.Buffered() > 0 {
-		netConn.Close()
 		return nil, errors.New("websocket: client sent data before handshake is complete")
 	}
 
@@ -247,20 +258,30 @@ func (u *Upgrader) Upgrade(w http.ResponseWriter, r *http.Request, responseHeade
 	}
 	p = append(p, "\r\n"...)
 
-	// Clear deadlines set by HTTP server.
-	netConn.SetDeadline(time.Time{})
-
 	if u.HandshakeTimeout > 0 {
-		netConn.SetWriteDeadline(time.Now().Add(u.HandshakeTimeout))
+		if err := netConn.SetWriteDeadline(time.Now().Add(u.HandshakeTimeout)); err != nil {
+			return nil, err
+		}
+	} else {
+		// Clear deadlines set by HTTP server.
+		if err := netConn.SetDeadline(time.Time{}); err != nil {
+			return nil, err
+		}
 	}
+
 	if _, err = netConn.Write(p); err != nil {
-		netConn.Close()
 		return nil, err
 	}
 	if u.HandshakeTimeout > 0 {
-		netConn.SetWriteDeadline(time.Time{})
+		if err := netConn.SetWriteDeadline(time.Time{}); err != nil {
+			return nil, err
+		}
 	}
 
+	// Success! Set netConn to nil to stop the deferred function above from
+	// closing the network connection.
+	netConn = nil
+
 	return c, nil
 }
 
@@ -356,7 +377,7 @@ func bufioWriterBuffer(originalWriter io.Writer, bw *bufio.Writer) []byte {
 	// bufio.Writer's underlying writer.
 	var wh writeHook
 	bw.Reset(&wh)
-	bw.WriteByte(0)
+	_ = bw.WriteByte(0)
 	bw.Flush()
 
 	bw.Reset(originalWriter)