Refactor errors and add support for Go 1.13 errors (#124)

* all: Implement Is, As and Unwrap for errors

* Deprecate cdp.ErrorCause in favor of Is, As, Unwrap

* Use errors.Is and errors.As where applicable

* travis: Drop Go 1.12, add Go 1.15

.travis.yml

@@ -6,9 +6,9 @@ addons:
   chrome: stable
 
 go:
-  - 1.12.x
   - 1.13.x
   - 1.14.x
+  - 1.15.x
   - master
 
 before_install:

error.go

@@ -6,4 +6,6 @@ import (
 
 // ErrorCause returns the underlying cause for this error, if possible.
 // If err does not implement causer.Cause(), then err is returned.
+//
+// Deprecated: Use errors.Unwrap, errors.Is or errors.As instead.
 func ErrorCause(err error) error { return errors.Cause(err) }

internal/errors/errors.go

@@ -1,21 +1,23 @@
 package errors
 
 import (
-	"errors"
 	"fmt"
 	"strings"
 )
 
-// Causer is an interface to access to its direct cause of the error.
-type Causer interface {
-	Cause() error
-}
+// Interfaces for common error unwrapping.
+type causer interface{ Cause() error }
+type wrapper interface{ Unwrap() error }
 
 // Cause returns the underlying cause for this error, if possible.
-// If err does not implement Causer.Cause(), then err is returned.
+// If err does not implement causer.Cause(), then err is returned.
+//
+// Deprecated: Use errors.Unwrap, errors.Is or errors.As instead.
 func Cause(err error) error {
 	for err != nil {
-		if c, ok := err.(Causer); ok {
+		if c, ok := err.(wrapper); ok {
+			err = c.Unwrap()
+		} else if c, ok := err.(causer); ok {
 			err = c.Cause()
 		} else {
 			return err
@@ -24,16 +26,6 @@ func Cause(err error) error {
 	return err
 }
 
-// New returns an error that formats as the given text.
-func New(text string) error {
-	return errors.New(text)
-}
-
-// Errorf wraps New and fmt.Sprintf.
-func Errorf(format string, a ...interface{}) error {
-	return New(fmt.Sprintf(format, a...))
-}
-
 // Wrapf wraps an error with a message. Wrapf returns nil if error is nil.
 func Wrapf(err error, format string, a ...interface{}) error {
 	if err == nil {
@@ -51,15 +43,12 @@ type wrapped struct {
 }
 
 var _ error = (*wrapped)(nil)
-var _ Causer = (*wrapped)(nil)
+var _ causer = (*wrapped)(nil)
+var _ wrapper = (*wrapped)(nil)
 
-func (e *wrapped) Error() string {
-	return fmt.Sprintf("%s: %s", e.msg, e.err)
-}
-
-func (e *wrapped) Cause() error {
-	return e.err
-}
+func (e *wrapped) Error() string { return fmt.Sprintf("%s: %s", e.msg, e.err.Error()) }
+func (e *wrapped) Cause() error  { return e.err }
+func (e *wrapped) Unwrap() error { return e.err }
 
 // Merge merges multiple errors into one.
 // Merge returns nil if all errors are nil.
@@ -73,14 +62,16 @@ func Merge(err ...error) error {
 	if len(errs) == 0 {
 		return nil
 	}
-	return &merged{s: err}
+	return &merged{s: errs}
 }
 
 type merged struct {
 	s []error
 }
 
 var _ error = (*merged)(nil)
+var _ causer = (*merged)(nil)
+var _ wrapper = (*merged)(nil)
 
 func (e *merged) Error() string {
 	var m []string
@@ -89,3 +80,34 @@ func (e *merged) Error() string {
 	}
 	return strings.Join(m, ": ")
 }
+
+// Unwrap returns only the first error, there is
+// no way to create a queue of errors.
+func (e *merged) Unwrap() error { return e.s[0] }
+
+// Cause returns only the first error, there is
+// no way to create a queue of errors.
+func (e *merged) Cause() error { return e.s[0] }
+
+// Is runs errors.Is on all merged errors.
+func (e *merged) Is(target error) bool {
+	if target == nil {
+		return nil == e.s
+	}
+	for _, err := range e.s {
+		if Is(err, target) {
+			return true
+		}
+	}
+	return false
+}
+
+// As runs errors.As on all merged errors.
+func (e *merged) As(target interface{}) bool {
+	for _, err := range e.s {
+		if As(err, target) {
+			return true
+		}
+	}
+	return false
+}

internal/errors/errors_test.go

@@ -50,6 +50,47 @@ func TestMergeError(t *testing.T) {
 	}
 }
 
+func TestMergeErrorIs(t *testing.T) {
+	err1 := errors.New("first")
+	err2 := errors.New("second")
+	err3 := errors.New("third")
+
+	got := Merge(err1, err2)
+
+	if !errors.Is(got, err1) {
+		t.Errorf("merged error is not err1, want true, got false")
+	}
+	if !errors.Is(got, err2) {
+		t.Errorf("merged error is not err2, want true, got false")
+	}
+	if errors.Is(got, err3) {
+		t.Errorf("merged error is err3, want false, got true")
+	}
+}
+
+type testErrorAs struct{ msg string }
+
+func (e testErrorAs) Error() string { return e.msg }
+
+func TestMergeErrorAs(t *testing.T) {
+	err1 := &wrapped{msg: "err1"}
+	err2 := testErrorAs{msg: "err2"}
+
+	err := Merge(err1, err2)
+	got1 := &wrapped{}
+	if !errors.As(err, &got1) {
+		t.Errorf("merged error as wrapped failed, want true, got false")
+	} else if got1.msg != "err1" {
+		t.Errorf("merged error as wrapped did not assign the error, want msg=err1, got msg=%s", got1.msg)
+	}
+	got2 := testErrorAs{}
+	if !errors.As(err, &got2) {
+		t.Errorf("merged error as testErrorAs failed, want true, got false")
+	} else if got2.Error() != "err2" {
+		t.Errorf("merged error as testErrorAs did not assign the error, want msg=err2, got msg=%s", got2.Error())
+	}
+}
+
 func TestMergeNoError(t *testing.T) {
 	got := Merge(nil, nil)
 	if got != nil {

internal/errors/stdlib.go

@@ -0,0 +1,64 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package errors
+
+import (
+	stderrors "errors"
+	"fmt"
+)
+
+// New returns an error that formats as the given text.
+// Each call to New returns a distinct error value even if the text is identical.
+func New(text string) error { return stderrors.New(text) }
+
+// Unwrap returns the result of calling the Unwrap method on err, if err's
+// type contains an Unwrap method returning error.
+// Otherwise, Unwrap returns nil.
+func Unwrap(err error) error { return stderrors.Unwrap(err) }
+
+// Is reports whether any error in err's chain matches target.
+//
+// The chain consists of err itself followed by the sequence of errors obtained by
+// repeatedly calling Unwrap.
+//
+// An error is considered to match a target if it is equal to that target or if
+// it implements a method Is(error) bool such that Is(target) returns true.
+//
+// An error type might provide an Is method so it can be treated as equivalent
+// to an existing error. For example, if MyError defines
+//
+//	func (m MyError) Is(target error) bool { return target == os.ErrExist }
+//
+// then Is(MyError{}, os.ErrExist) returns true. See syscall.Errno.Is for
+// an example in the standard library.
+func Is(err, target error) bool { return stderrors.Is(err, target) }
+
+// As finds the first error in err's chain that matches target, and if so, sets
+// target to that error value and returns true. Otherwise, it returns false.
+//
+// The chain consists of err itself followed by the sequence of errors obtained by
+// repeatedly calling Unwrap.
+//
+// An error matches target if the error's concrete value is assignable to the value
+// pointed to by target, or if the error has a method As(interface{}) bool such that
+// As(target) returns true. In the latter case, the As method is responsible for
+// setting target.
+//
+// An error type might provide an As method so it can be treated as if it were a
+// different error type.
+//
+// As panics if target is not a non-nil pointer to either a type that implements
+// error, or to any interface type.
+func As(err error, target interface{}) bool { return stderrors.As(err, target) }
+
+// Errorf formats according to a format specifier and returns the string as a
+// value that satisfies error.
+//
+// If the format specifier includes a %w verb with an error operand,
+// the returned error will implement an Unwrap method returning the operand. It is
+// invalid to include more than one %w verb or to supply it with an operand
+// that does not implement the error interface. The %w verb is otherwise
+// a synonym for %v.
+func Errorf(format string, a ...interface{}) error { return fmt.Errorf(format, a...) }

protocol/internal/error.go

@@ -11,20 +11,25 @@ type OpError struct {
 	Err    error
 }
 
+func (e OpError) Error() string {
+	return fmt.Sprintf("cdp.%s: %s: %s", e.Domain, e.Op, e.Err.Error())
+}
+
 // Cause implements error causer.
 func (e *OpError) Cause() error {
 	return e.Err
 }
 
-func (e OpError) Error() string {
-	return fmt.Sprintf("cdp.%s: %s: %s", e.Domain, e.Op, e.Err.Error())
+// Unwrap implements Wrapper.
+func (e *OpError) Unwrap() error {
+	return e.Err
 }
 
-type causer interface {
-	Cause() error
-}
+type causer interface{ Cause() error }
+type wrapper interface{ Unwrap() error }
 
 var (
-	_ error  = (*OpError)(nil)
-	_ causer = (*OpError)(nil)
+	_ error   = (*OpError)(nil)
+	_ causer  = (*OpError)(nil)
+	_ wrapper = (*OpError)(nil)
 )

rpcc/conn.go

@@ -25,8 +25,9 @@ func (e *closeError) Error() string {
 	}
 	return e.msg
 }
-func (e *closeError) Closed() bool { return true }
-func (e *closeError) Cause() error { return e.err }
+func (e *closeError) Closed() bool  { return true }
+func (e *closeError) Cause() error  { return e.err }
+func (e *closeError) Unwrap() error { return e.err }
 
 var (
 	// ErrConnClosing indicates that the operation is illegal because

session/manager.go

@@ -70,22 +70,17 @@ func (m *Manager) watch(ev *sessionEvents, created <-chan *session, done, errC c
 	defer ev.Close()
 
 	isClosing := func(err error) bool {
-		for e := err;; {
-			// Test if this is an rpcc.closeError.
-			if v, ok := e.(interface{ Closed() bool }); ok && v.Closed() {
-				// Cleanup, the underlying connection was closed
-				// before the Manager and its context does not
-				// inherit from rpcc.Conn.
-				m.cancel()
-				return true
-			}
-			if v, ok := e.(errors.Causer); ok {
-				e = v.Cause()
-			} else {
-				break
-			}
+		// Test if this is an rpcc.closeError.
+		var e interface{ Closed() bool }
+		if ok := errors.As(err, &e); ok && e.Closed() {
+			// Cleanup, the underlying connection was closed
+			// before the Manager and its context does not
+			// inherit from rpcc.Conn.
+			m.cancel()
+			return true
 		}
-		if cdp.ErrorCause(err) == context.Canceled {
+
+		if errors.Is(err, context.Canceled) {
 			// Manager was closed.
 			return true
 		}

session/manager_test.go

@@ -64,7 +64,7 @@ func TestManager_ErrorsAreSentOnErrChan(t *testing.T) {
 	detached.err = errors.New("detach nope")
 	detached.markReady()
 	err := <-m.Err()
-	if err := errors.Cause(err); err != detached.err {
+	if !errors.Is(err, detached.err) {
 		t.Errorf("got error: %v; want: %v", err, detached.err)
 	}
 	detached.next()
@@ -73,7 +73,7 @@ func TestManager_ErrorsAreSentOnErrChan(t *testing.T) {
 	message.err = errors.New("message nope")
 	message.markReady()
 	err = <-m.Err()
-	if err := errors.Cause(err); err != message.err {
+	if !errors.Is(err, message.err) {
 		t.Errorf("got error: %v; want: %v", err, message.err)
 	}
 	message.next()

session/session.go

@@ -118,7 +118,7 @@ func dial(ctx context.Context, id target.ID, tc *cdp.Client, detachTimeout time.
 
 		err := tc.Target.DetachFromTarget(ctx,
 			target.NewDetachFromTargetArgs().SetSessionID(s.ID))
-		if err := cdp.ErrorCause(err); err == context.DeadlineExceeded {
+		if errors.Is(err, context.DeadlineExceeded) {
 			return fmt.Errorf("session: detach timed out for session %s", s.ID)
 		}
 		return errors.Wrapf(err, "session: detach failed for session %s", s.ID)