Use errors.As and errors.Is

Replace type assertions to error types with errors.As. Replace
comparisons with error values with errors.Is.

compression.go

@@ -131,7 +131,7 @@ func (r *flateReadWrapper) Read(p []byte) (int, error) {
 		return 0, io.ErrClosedPipe
 	}
 	n, err := r.fr.Read(p)
-	if err == io.EOF {
+	if errors.Is(err, io.EOF) {
 		// Preemptively place the reader back in the pool. This helps with
 		// scenarios where the application does not call NextReader() soon after
 		// this final read.

conn.go

@@ -149,7 +149,8 @@ func (e *CloseError) Error() string {
 // IsCloseError returns boolean indicating whether the error is a *CloseError
 // with one of the specified codes.
 func IsCloseError(err error, codes ...int) bool {
-	if e, ok := err.(*CloseError); ok {
+	var e *CloseError
+	if errors.As(err, &e) {
 		for _, code := range codes {
 			if e.Code == code {
 				return true
@@ -162,7 +163,8 @@ func IsCloseError(err error, codes ...int) bool {
 // IsUnexpectedCloseError returns boolean indicating whether the error is a
 // *CloseError with a code not in the list of expected codes.
 func IsUnexpectedCloseError(err error, expectedCodes ...int) bool {
-	if e, ok := err.(*CloseError); ok {
+	var e *CloseError
+	if errors.As(err, &e) {
 		for _, code := range expectedCodes {
 			if e.Code == code {
 				return false
@@ -376,7 +378,7 @@ func (c *Conn) writeFatal(err error) error {
 
 func (c *Conn) read(n int) ([]byte, error) {
 	p, err := c.br.Peek(n)
-	if err == io.EOF {
+	if errors.Is(err, io.EOF) {
 		err = errUnexpectedEOF
 	}
 	if _, err := c.br.Discard(len(p)); err != nil {
@@ -730,7 +732,7 @@ func (w *messageWriter) ReadFrom(r io.Reader) (nn int64, err error) {
 		w.pos += n
 		nn += int64(n)
 		if err != nil {
-			if err == io.EOF {
+			if errors.Is(err, io.EOF) {
 				err = nil
 			}
 			break
@@ -1082,7 +1084,7 @@ func (r *messageReader) Read(b []byte) (int, error) {
 			if err := c.setReadRemaining(rem); err != nil {
 				return 0, err
 			}
-			if c.readRemaining > 0 && c.readErr == io.EOF {
+			if c.readRemaining > 0 && errors.Is(c.readErr, io.EOF) {
 				c.readErr = errUnexpectedEOF
 			}
 			return n, c.readErr
@@ -1103,7 +1105,7 @@ func (r *messageReader) Read(b []byte) (int, error) {
 	}
 
 	err := c.readErr
-	if err == io.EOF && c.messageReader == r {
+	if errors.Is(err, io.EOF) && c.messageReader == r {
 		err = errUnexpectedEOF
 	}
 	return 0, err

conn_test.go

@@ -404,18 +404,18 @@ func TestEOFWithinFrame(t *testing.T) {
 		b.Truncate(n)
 
 		op, r, err := rc.NextReader()
-		if err == errUnexpectedEOF {
+		if errors.Is(err, errUnexpectedEOF) {
 			continue
 		}
 		if op != BinaryMessage || err != nil {
 			t.Fatalf("%d: NextReader() returned %d, %v", n, op, err)
 		}
 		_, err = io.Copy(io.Discard, r)
-		if err != errUnexpectedEOF {
+		if !errors.Is(err, errUnexpectedEOF) {
 			t.Fatalf("%d: io.Copy() returned %v, want %v", n, err, errUnexpectedEOF)
 		}
 		_, _, err = rc.NextReader()
-		if err != errUnexpectedEOF {
+		if !errors.Is(err, errUnexpectedEOF) {
 			t.Fatalf("%d: NextReader() returned %v, want %v", n, err, errUnexpectedEOF)
 		}
 	}
@@ -438,11 +438,11 @@ func TestEOFBeforeFinalFrame(t *testing.T) {
 		t.Fatalf("NextReader() returned %d, %v", op, err)
 	}
 	_, err = io.Copy(io.Discard, r)
-	if err != errUnexpectedEOF {
+	if !errors.Is(err, errUnexpectedEOF) {
 		t.Fatalf("io.Copy() returned %v, want %v", err, errUnexpectedEOF)
 	}
 	_, _, err = rc.NextReader()
-	if err != errUnexpectedEOF {
+	if !errors.Is(err, errUnexpectedEOF) {
 		t.Fatalf("NextReader() returned %v, want %v", err, errUnexpectedEOF)
 	}
 }
@@ -514,7 +514,7 @@ func TestReadLimit(t *testing.T) {
 			t.Fatalf("2: NextReader() returned %d, %v", op, err)
 		}
 		_, err = io.Copy(io.Discard, r)
-		if err != ErrReadLimit {
+		if !errors.Is(err, ErrReadLimit) {
 			t.Fatalf("io.Copy() returned %v", err)
 		}
 	})
@@ -558,13 +558,13 @@ func TestReadLimit(t *testing.T) {
 		var buf [10]byte
 		var read int
 		n, err := r.Read(buf[:])
-		if err != nil && err != ErrReadLimit {
+		if err != nil && !errors.Is(err, ErrReadLimit) {
 			t.Fatalf("unexpected error testing read limit: %v", err)
 		}
 		read += n
 
 		n, err = r.Read(buf[:])
-		if err != nil && err != ErrReadLimit {
+		if err != nil && !errors.Is(err, ErrReadLimit) {
 			t.Fatalf("unexpected error testing read limit: %v", err)
 		}
 		read += n

join.go

@@ -5,6 +5,7 @@
 package websocket
 
 import (
+	"errors"
 	"io"
 	"strings"
 )
@@ -34,7 +35,7 @@ func (r *joinReader) Read(p []byte) (int, error) {
 		}
 	}
 	n, err := r.r.Read(p)
-	if err == io.EOF {
+	if errors.Is(err, io.EOF) {
 		err = nil
 		r.r = nil
 	}

json.go

@@ -6,6 +6,7 @@ package websocket
 
 import (
 	"encoding/json"
+	"errors"
 	"io"
 )
 
@@ -52,7 +53,7 @@ func (c *Conn) ReadJSON(v interface{}) error {
 		return err
 	}
 	err = json.NewDecoder(r).Decode(v)
-	if err == io.EOF {
+	if errors.Is(err, io.EOF) {
 		// One value is expected in the message.
 		err = io.ErrUnexpectedEOF
 	}

json_test.go

@@ -7,6 +7,7 @@ package websocket
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"io"
 	"reflect"
 	"testing"
@@ -79,13 +80,14 @@ func TestPartialJSONRead(t *testing.T) {
 
 	for i := 0; i < messageCount; i++ {
 		err := rc.ReadJSON(&v)
-		if err != io.ErrUnexpectedEOF {
+		if !errors.Is(err, io.ErrUnexpectedEOF) {
 			t.Error("read", i, err)
 		}
 	}
 
 	err = rc.ReadJSON(&v)
-	if _, ok := err.(*CloseError); !ok {
+	var ce *CloseError
+	if !errors.As(err, &ce) {
 		t.Error("final", err)
 	}
 }