Wrap error (#65)

client_test.go

@@ -19,6 +19,8 @@ import (
 	"net"
 	"testing"
 	"time"
+
+	"github.com/at-wat/mqtt-go/internal/errs"
 )
 
 func TestProtocolViolation(t *testing.T) {
@@ -79,7 +81,7 @@ func TestProtocolViolation(t *testing.T) {
 
 	select {
 	case err := <-errCh:
-		if err != ErrInvalidPacket {
+		if !errs.Is(err, ErrInvalidPacket) {
 			t.Errorf("Expected error against invalid packet: '%v', got: '%v'", ErrInvalidPacket, err)
 		}
 	case <-ctx.Done():

conn.go

@@ -127,7 +127,7 @@ func (d *DialOptions) dial(urlStr string) (*BaseClient, error) {
 		ws.PayloadType = websocket.BinaryFrame
 		c.Transport = ws
 	default:
-		return nil, ErrUnsupportedProtocol
+		return nil, wrapErrorf(ErrUnsupportedProtocol, "protocol %s", u.Scheme)
 	}
 	return c, nil
 }

connack.go

@@ -56,10 +56,10 @@ type pktConnAck struct {
 
 func (p *pktConnAck) parse(flag byte, contents []byte) (*pktConnAck, error) {
 	if flag != 0 {
-		return nil, ErrInvalidPacket
+		return nil, wrapError(ErrInvalidPacket, "parsing CONNACK")
 	}
 	if len(contents) != 2 {
-		return nil, ErrInvalidPacketLength
+		return nil, wrapError(ErrInvalidPacketLength, "parsing CONNACK")
 	}
 	return &pktConnAck{
 		SessionPresent: (contents[0]&0x01 != 0),

connect.go

@@ -142,7 +142,7 @@ func (c *BaseClient) Connect(ctx context.Context, clientID string, opts ...Conne
 	}).pack()
 
 	if err := c.write(pkt); err != nil {
-		return false, err
+		return false, wrapError(err, "sending CONNECT")
 	}
 	select {
 	case <-c.connClosed:

disconnect.go

@@ -26,7 +26,7 @@ func (c *BaseClient) Disconnect(ctx context.Context) error {
 	pkt := pack(packetDisconnect.b())
 	c.connStateUpdate(StateDisconnected)
 	if err := c.write(pkt); err != nil {
-		return err
+		return wrapError(err, "sending DISCONNECT")
 	}
 	c.Transport.Close()
 	return nil

error.go

@@ -0,0 +1,87 @@
+// Copyright 2019 The mqtt-go authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mqtt
+
+import (
+	"fmt"
+	"reflect"
+)
+
+// Error records a failed parsing.
+type Error struct {
+	Err     error
+	Failure string
+}
+
+func (e *Error) Error() string {
+	// TODO: migrate to fmt.Sprintf %w once Go1.12 reaches EOL.
+	return e.Failure + ": " + e.Err.Error()
+}
+
+// Unwrap returns the reason of the failure.
+// This is for Go1.13 error unwrapping.
+func (e *Error) Unwrap() error {
+	return e.Err
+}
+
+// Is reports whether chained error contains target.
+// This is for Go1.13 error unwrapping.
+func (e *Error) Is(target error) bool {
+	err := e.Err
+
+	switch target {
+	case e:
+		return true
+	case nil:
+		return err == nil
+	}
+	for {
+		switch err {
+		case nil:
+			return false
+		case target:
+			return true
+		}
+		x, ok := err.(interface{ Unwrap() error })
+		if !ok {
+			// Some stdlibs haven't have error unwrapper yet.
+			// Check err.Err field if exposed.
+			if reflect.TypeOf(err).Kind() == reflect.Ptr {
+				e := reflect.ValueOf(err).Elem().FieldByName("Err")
+				if e.IsValid() {
+					e2, ok := e.Interface().(error)
+					if !ok {
+						return false
+					}
+					err = e2
+					continue
+				}
+			}
+			return false
+		}
+		err = x.Unwrap()
+	}
+}
+
+func wrapError(err error, failure string) error {
+	return &Error{
+		Failure: failure,
+		Err:     err,
+	}
+}
+
+func wrapErrorf(err error, failureFmt string, v ...interface{}) error {
+	return wrapError(err, fmt.Sprintf(failureFmt, v...))
+}

error_test.go

@@ -0,0 +1,87 @@
+// Copyright 2019 The mqtt-go authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mqtt
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/at-wat/mqtt-go/internal/errs"
+)
+
+type dummyError struct {
+	Err error
+}
+
+func (e *dummyError) Error() string {
+	return e.Err.Error()
+}
+
+func TestError(t *testing.T) {
+	errBase := errors.New("an error")
+	errOther := errors.New("an another error")
+	errChained := wrapErrorf(errBase, "info")
+	errDoubleChained := wrapErrorf(errChained, "info")
+	errChainedNil := wrapErrorf(nil, "info")
+	errChainedOther := wrapErrorf(errOther, "info")
+	err112Chained := wrapErrorf(&dummyError{errBase}, "info")
+	err112Nil := wrapErrorf(&dummyError{nil}, "info")
+	errStr := "info: an error"
+
+	t.Run("ErrorsIs", func(t *testing.T) {
+		if !errs.Is(errChained, errBase) {
+			t.Errorf("Wrapped error '%v' doesn't chain '%v'", errChained, errBase)
+		}
+	})
+
+	t.Run("Is", func(t *testing.T) {
+		if !errChained.(*Error).Is(errChained) {
+			t.Errorf("Wrapped error '%v' doesn't match its-self", errChained)
+		}
+		if !errChained.(*Error).Is(errBase) {
+			t.Errorf("Wrapped error '%v' doesn't match '%v'", errChained, errBase)
+		}
+		if !errDoubleChained.(*Error).Is(errBase) {
+			t.Errorf("Wrapped error '%v' doesn't match '%v'", errDoubleChained, errBase)
+		}
+		if !err112Chained.(*Error).Is(errBase) {
+			t.Errorf("Wrapped error '%v' doesn't match '%v'",
+				err112Chained, errBase)
+		}
+		if !errChainedNil.(*Error).Is(nil) {
+			t.Errorf("Nil chained error '%v' doesn't match 'nil'", errChainedNil)
+		}
+
+		if errChainedNil.(*Error).Is(errBase) {
+			t.Errorf("Wrapped error '%v' unexpectedly matched '%v'",
+				errChainedNil, errBase)
+		}
+		if errChainedOther.(*Error).Is(errBase) {
+			t.Errorf("Wrapped error '%v' unexpectedly matched '%v'",
+				errChainedOther, errBase)
+		}
+		if err112Nil.(*Error).Is(errBase) {
+			t.Errorf("Wrapped error '%v' unexpectedly matched '%v'",
+				errChainedOther, errBase)
+		}
+	})
+
+	if errChained.Error() != errStr {
+		t.Errorf("Error string expected: %s, got: %s", errStr, errChained.Error())
+	}
+	if errChained.(*Error).Unwrap() != errBase {
+		t.Errorf("Unwrapped error expected: %s, got: %s", errBase, errChained.(*Error).Unwrap())
+	}
+}

filter.go

@@ -26,20 +26,20 @@ type topicFilter []string
 
 func newTopicFilter(filter string) (topicFilter, error) {
 	if len(filter) == 0 {
-		return nil, ErrInvalidTopicFilter
+		return nil, wrapError(ErrInvalidTopicFilter, "empty filter")
 	}
 	tf := strings.Split(filter, "/")
 
 	// Validate according to MQTT 3.1.1 spec. 4.7.1
 	for i, f := range tf {
 		if strings.Contains(f, "+") {
 			if len(f) != 1 {
-				return nil, ErrInvalidTopicFilter
+				return nil, wrapError(ErrInvalidTopicFilter, "invalid + usage")
 			}
 		}
 		if strings.Contains(f, "#") {
 			if len(f) != 1 || i != len(tf)-1 {
-				return nil, ErrInvalidTopicFilter
+				return nil, wrapError(ErrInvalidTopicFilter, "invalid # usage")
 			}
 		}
 	}

internal/errs/errors_112.go

@@ -0,0 +1,40 @@
+// +build !go1.13
+
+// Copyright 2019 The mqtt-go authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package errs
+
+// Is compares error type. Works like Go1.13 errors.Is().
+func Is(err, target error) bool {
+	if target == nil {
+		return err == nil
+	}
+	for {
+		if err == target {
+			return true
+		}
+		if err == nil {
+			return false
+		}
+		if x, ok := err.(interface{ Is(error) bool }); ok {
+			return x.Is(target)
+		}
+		x, ok := err.(interface{ Unwrap() error })
+		if !ok {
+			return false
+		}
+		err = x.Unwrap()
+	}
+}

internal/errs/errors_113.go

@@ -0,0 +1,27 @@
+// +build go1.13
+
+// Copyright 2019 The mqtt-go authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package errs is for compatibility with Go1.13 error wrapping.
+package errs
+
+import (
+	"errors"
+)
+
+// Is compares error type. Wrapping Go1.13 errors.Is().
+func Is(err, target error) bool {
+	return errors.Is(err, target)
+}