all: add Unwrap and Is methods to various error types

Add Unwrap methods to types which wrap an underlying error:

  "encodinc/csv".ParseError
  "encoding/json".MarshalerError
  "net/http".transportReadFromServerError
  "net".OpError
  "net".DNSConfigError
  "net/url".Error
  "os/exec".Error
  "signal/internal/pty".PtyError
  "text/template".ExecError

Add os.ErrTemporary. A case could be made for putting this error
value in package net, since no exported error types in package os
include a Temporary method. However, syscall errors returned from
the os package do include this method.

Add Is methods to error types with a Timeout or Temporary method,
making errors.Is(err, os.Err{Timeout,Temporary}) equivalent to
testing the corresponding method:

  "context".DeadlineExceeded
  "internal/poll".TimeoutError
  "net".adrinfoErrno
  "net".OpError
  "net".DNSError
  "net/http".httpError
  "net/http".tlsHandshakeTimeoutError
  "net/pipe".timeoutError
  "net/url".Error

Updates #30322
Updates #29934

Change-Id: I409fb20c072ea39116ebfb8c7534d493483870dc
Reviewed-on: https://go-review.googlesource.com/c/go/+/170037
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

18 files changed, 208 insertions, 24 deletions

diff --git a/src/context/context.go b/src/context/context.go
index 93bf5b627d..0f36881b1e 100644
--- a/src/context/context.go
+++ b/src/context/context.go
@@ -49,6 +49,7 @@ package context
 
 import (
 	"errors"
+	"internal/oserror"
 	"internal/reflectlite"
 	"sync"
 	"time"
@@ -162,6 +163,9 @@ type deadlineExceededError struct{}
 func (deadlineExceededError) Error() string   { return "context deadline exceeded" }
 func (deadlineExceededError) Timeout() bool   { return true }
 func (deadlineExceededError) Temporary() bool { return true }
+func (deadlineExceededError) Is(target error) bool {
+	return target == oserror.ErrTimeout || target == oserror.ErrTemporary
+}
 
 // An emptyCtx is never canceled, has no values, and has no deadline. It is not
 // struct{}, since vars of this type must have distinct addresses.
diff --git a/src/context/context_test.go b/src/context/context_test.go
index 0e69e2f6fd..9991c5b09c 100644
--- a/src/context/context_test.go
+++ b/src/context/context_test.go
@@ -5,8 +5,10 @@
 package context
 
 import (
+	"errors"
 	"fmt"
 	"math/rand"
+	"os"
 	"runtime"
 	"strings"
 	"sync"
@@ -647,4 +649,7 @@ func XTestDeadlineExceededSupportsTimeout(t testingT) {
 	if !i.Timeout() {
 		t.Fatal("wrong value for timeout")
 	}
+	if !errors.Is(DeadlineExceeded, os.ErrTimeout) {
+		t.Fatal("errors.Is(DeadlineExceeded, os.ErrTimeout) = false, want true")
+	}
 }
diff --git a/src/encoding/csv/reader.go b/src/encoding/csv/reader.go
index a2fd4c0970..c40aa506b0 100644
--- a/src/encoding/csv/reader.go
+++ b/src/encoding/csv/reader.go
@@ -80,6 +80,8 @@ func (e *ParseError) Error() string {
 	return fmt.Sprintf("parse error on line %d, column %d: %v", e.Line, e.Column, e.Err)
 }
 
+func (e *ParseError) Unwrap() error { return e.Err }
+
 // These are the errors that can be returned in ParseError.Err.
 var (
 	ErrTrailingComma = errors.New("extra delimiter at end of line") // Deprecated: No longer used.
diff --git a/src/encoding/json/encode.go b/src/encoding/json/encode.go
index 383460e52b..464ee3ece4 100644
--- a/src/encoding/json/encode.go
+++ b/src/encoding/json/encode.go
@@ -270,6 +270,8 @@ func (e *MarshalerError) Error() string {
 	return "json: error calling MarshalJSON for type " + e.Type.String() + ": " + e.Err.Error()
 }
 
+func (e *MarshalerError) Unwrap() error { return e.Err }
+
 var hex = "0123456789abcdef"
 
 // An encodeState encodes JSON into a bytes.Buffer.
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index f38f13a6f2..006edb6923 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -140,6 +140,7 @@ var pkgDeps = map[string][]string{
 		"image/color",
 		"image/color/palette",
 		"internal/fmtsort",
+		"internal/oserror",
 		"reflect",
 	},
 
@@ -166,7 +167,7 @@ var pkgDeps = map[string][]string{
 		"syscall/js",
 	},
 
-	"internal/poll":    {"L0", "internal/race", "syscall", "time", "unicode/utf16", "unicode/utf8", "internal/syscall/windows"},
+	"internal/poll":    {"L0", "internal/oserror", "internal/race", "syscall", "time", "unicode/utf16", "unicode/utf8", "internal/syscall/windows"},
 	"internal/testlog": {"L0"},
 	"os":               {"L1", "os", "syscall", "time", "internal/oserror", "internal/poll", "internal/syscall/windows", "internal/syscall/unix", "internal/testlog"},
 	"path/filepath":    {"L2", "os", "syscall", "internal/syscall/windows"},
@@ -249,7 +250,7 @@ var pkgDeps = map[string][]string{
 	"compress/gzip":                  {"L4", "compress/flate"},
 	"compress/lzw":                   {"L4"},
 	"compress/zlib":                  {"L4", "compress/flate"},
-	"context":                        {"errors", "internal/reflectlite", "sync", "time"},
+	"context":                        {"errors", "internal/oserror", "internal/reflectlite", "sync", "time"},
 	"database/sql":                   {"L4", "container/list", "context", "database/sql/driver", "database/sql/internal"},
 	"database/sql/driver":            {"L4", "context", "time", "database/sql/internal"},
 	"debug/dwarf":                    {"L4"},
diff --git a/src/internal/oserror/errors.go b/src/internal/oserror/errors.go
index 66ed7faaba..8bd17c8b56 100644
--- a/src/internal/oserror/errors.go
+++ b/src/internal/oserror/errors.go
@@ -15,6 +15,50 @@ var (
 	ErrExist      = errors.New("file already exists")
 	ErrNotExist   = errors.New("file does not exist")
 	ErrClosed     = errors.New("file already closed")
-	ErrTemporary  = errors.New("temporary error")
-	ErrTimeout    = errors.New("deadline exceeded")
+	ErrTemporary  = temporaryError{}
+	ErrTimeout    = timeoutError{}
 )
+
+type timeoutError struct{}
+
+func (timeoutError) Error() string { return "deadline exceeded" }
+func (timeoutError) Timeout() bool { return true }
+
+type temporaryError struct{}
+
+func (temporaryError) Error() string   { return "temporary error" }
+func (temporaryError) Temporary() bool { return true }
+
+// IsTimeout reports whether err indicates a timeout.
+func IsTimeout(err error) bool {
+	for err != nil {
+		if err == ErrTimeout {
+			return true
+		}
+		if x, ok := err.(interface{ Timeout() bool }); ok {
+			return x.Timeout()
+		}
+		if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(ErrTimeout) {
+			return true
+		}
+		err = errors.Unwrap(err)
+	}
+	return false
+}
+
+// IsTemporary reports whether err indicates a temporary condition.
+func IsTemporary(err error) bool {
+	for err != nil {
+		if err == ErrTemporary {
+			return true
+		}
+		if x, ok := err.(interface{ Temporary() bool }); ok {
+			return x.Temporary()
+		}
+		if x, ok := err.(interface{ Is(error) bool }); ok && x.Is(ErrTemporary) {
+			return true
+		}
+		err = errors.Unwrap(err)
+	}
+	return false
+}
diff --git a/src/internal/oserror/errors_test.go b/src/internal/oserror/errors_test.go
new file mode 100644
index 0000000000..6d6a56a0c7
--- /dev/null
+++ b/src/internal/oserror/errors_test.go
@@ -0,0 +1,63 @@
+package oserror_test
+
+import (
+	"errors"
+	"fmt"
+	"internal/oserror"
+	"os"
+	"testing"
+)
+
+type ttError struct {
+	timeout   bool
+	temporary bool
+}
+
+func (e ttError) Error() string {
+	return fmt.Sprintf("ttError{timeout:%v temporary:%v}", e.timeout, e.temporary)
+}
+func (e ttError) Timeout() bool   { return e.timeout }
+func (e ttError) Temporary() bool { return e.temporary }
+
+type isError struct {
+	err error
+}
+
+func (e isError) Error() string        { return fmt.Sprintf("isError(%v)", e.err) }
+func (e isError) Is(target error) bool { return e.err == target }
+
+func TestIsTimeout(t *testing.T) {
+	for _, test := range []struct {
+		want bool
+		err  error
+	}{
+		{true, ttError{timeout: true}},
+		{true, isError{os.ErrTimeout}},
+		{true, os.ErrTimeout},
+		{true, fmt.Errorf("wrap: %w", os.ErrTimeout)},
+		{false, ttError{timeout: false}},
+		{false, errors.New("error")},
+	} {
+		if got, want := oserror.IsTimeout(test.err), test.want; got != want {
+			t.Errorf("IsTimeout(err) = %v, want %v\n%+v", got, want, test.err)
+		}
+	}
+}
+
+func TestIsTemporary(t *testing.T) {
+	for _, test := range []struct {
+		want bool
+		err  error
+	}{
+		{true, ttError{temporary: true}},
+		{true, isError{os.ErrTemporary}},
+		{true, os.ErrTemporary},
+		{true, fmt.Errorf("wrap: %w", os.ErrTemporary)},
+		{false, ttError{temporary: false}},
+		{false, errors.New("error")},
+	} {
+		if got, want := oserror.IsTemporary(test.err), test.want; got != want {
+			t.Errorf("IsTemporary(err) = %v, want %v\n%+v", got, want, test.err)
+		}
+	}
+}
diff --git a/src/internal/poll/fd.go b/src/internal/poll/fd.go
index 2ab86f2314..784bea4b5a 100644
--- a/src/internal/poll/fd.go
+++ b/src/internal/poll/fd.go
@@ -9,7 +9,10 @@
 // runtime scheduler.
 package poll
 
-import "errors"
+import (
+	"errors"
+	"internal/oserror"
+)
 
 // ErrNetClosing is returned when a network descriptor is used after
 // it has been closed. Keep this string consistent because of issue
@@ -44,6 +47,10 @@ func (e *TimeoutError) Error() string   { return "i/o timeout" }
 func (e *TimeoutError) Timeout() bool   { return true }
 func (e *TimeoutError) Temporary() bool { return true }
 
+func (e *TimeoutError) Is(target error) bool {
+	return target == oserror.ErrTimeout || target == oserror.ErrTemporary
+}
+
 // ErrNotPollable is returned when the file or socket is not suitable
 // for event notification.
 var ErrNotPollable = errors.New("not pollable")
diff --git a/src/net/cgo_unix.go b/src/net/cgo_unix.go
index 69c99fe7db..b9a6ffaa60 100644
--- a/src/net/cgo_unix.go
+++ b/src/net/cgo_unix.go
@@ -24,6 +24,7 @@ import "C"
 
 import (
 	"context"
+	"os"
 	"syscall"
 	"unsafe"
 )
@@ -37,6 +38,16 @@ func (eai addrinfoErrno) Error() string   { return C.GoString(C.gai_strerror(C.i
 func (eai addrinfoErrno) Temporary() bool { return eai == C.EAI_AGAIN }
 func (eai addrinfoErrno) Timeout() bool   { return false }
 
+func (eai addrinfoErrno) Is(target error) bool {
+	switch target {
+	case os.ErrTemporary:
+		return eai.Temporary()
+	case os.ErrTimeout:
+		return eai.Timeout()
+	}
+	return false
+}
+
 type portLookupResult struct {
 	port int
 	err  error
diff --git a/src/net/http/transport.go b/src/net/http/transport.go
index 20bfe0942d..5a1ebaac4c 100644
--- a/src/net/http/transport.go
+++ b/src/net/http/transport.go
@@ -788,6 +788,8 @@ type transportReadFromServerError struct {
 	err error
 }
 
+func (e transportReadFromServerError) Unwrap() error { return e.err }
+
 func (e transportReadFromServerError) Error() string {
 	return fmt.Sprintf("net/http: Transport failed to read from server: %v", e.err)
 }
@@ -2155,6 +2157,16 @@ func (e *httpError) Error() string   { return e.err }
 func (e *httpError) Timeout() bool   { return e.timeout }
 func (e *httpError) Temporary() bool { return true }
 
+func (e *httpError) Is(target error) bool {
+	switch target {
+	case os.ErrTimeout:
+		return e.timeout
+	case os.ErrTemporary:
+		return true
+	}
+	return false
+}
+
 var errTimeout error = &httpError{err: "net/http: timeout awaiting response headers", timeout: true}
 
 // errRequestCanceled is set to be identical to the one from h2 to facilitate
@@ -2489,6 +2501,10 @@ func (tlsHandshakeTimeoutError) Timeout() bool   { return true }
 func (tlsHandshakeTimeoutError) Temporary() bool { return true }
 func (tlsHandshakeTimeoutError) Error() string   { return "net/http: TLS handshake timeout" }
 
+func (tlsHandshakeTimeoutError) Is(target error) bool {
+	return target == os.ErrTimeout || target == os.ErrTemporary
+}
+
 // fakeLocker is a sync.Locker which does nothing. It's used to guard
 // test-only fields when not under test, to avoid runtime atomic
 // overhead.
diff --git a/src/net/net.go b/src/net/net.go
index 0e078620a5..b3f9b8ba07 100644
--- a/src/net/net.go
+++ b/src/net/net.go
@@ -448,6 +448,8 @@ type OpError struct {
 	Err error
 }
 
+func (e *OpError) Unwrap() error { return e.Err }
+
 func (e *OpError) Error() string {
 	if e == nil {
 		return "<nil>"
@@ -514,6 +516,16 @@ func (e *OpError) Temporary() bool {
 	return ok && t.Temporary()
 }
 
+func (e *OpError) Is(target error) bool {
+	switch target {
+	case os.ErrTemporary:
+		return e.Temporary()
+	case os.ErrTimeout:
+		return e.Timeout()
+	}
+	return false
+}
+
 // A ParseError is the error type of literal network address parsers.
 type ParseError struct {
 	// Type is the type of string that was expected, such as
@@ -563,6 +575,7 @@ type DNSConfigError struct {
 	Err error
 }
 
+func (e *DNSConfigError) Unwrap() error   { return e.Err }
 func (e *DNSConfigError) Error() string   { return "error reading DNS config: " + e.Err.Error() }
 func (e *DNSConfigError) Timeout() bool   { return false }
 func (e *DNSConfigError) Temporary() bool { return false }
@@ -604,6 +617,16 @@ func (e *DNSError) Timeout() bool { return e.IsTimeout }
 // error and return a DNSError for which Temporary returns false.
 func (e *DNSError) Temporary() bool { return e.IsTimeout || e.IsTemporary }
 
+func (e *DNSError) Is(target error) bool {
+	switch target {
+	case os.ErrTemporary:
+		return e.Temporary()
+	case os.ErrTimeout:
+		return e.Timeout()
+	}
+	return false
+}
+
 type writerOnly struct {
 	io.Writer
 }
diff --git a/src/net/pipe.go b/src/net/pipe.go
index 9177fc4036..8cc127464b 100644
--- a/src/net/pipe.go
+++ b/src/net/pipe.go
@@ -6,6 +6,7 @@ package net
 
 import (
 	"io"
+	"os"
 	"sync"
 	"time"
 )
@@ -84,6 +85,10 @@ func (timeoutError) Error() string   { return "deadline exceeded" }
 func (timeoutError) Timeout() bool   { return true }
 func (timeoutError) Temporary() bool { return true }
 
+func (timeoutError) Is(target error) bool {
+	return target == os.ErrTemporary || target == os.ErrTimeout
+}
+
 type pipeAddr struct{}
 
 func (pipeAddr) Network() string { return "pipe" }
diff --git a/src/net/timeout_test.go b/src/net/timeout_test.go
index 9599fa1d3e..4b9fe7eba9 100644
--- a/src/net/timeout_test.go
+++ b/src/net/timeout_test.go
@@ -7,7 +7,9 @@
 package net
 
 import (
+	"errors"
 	"fmt"
+	"internal/oserror"
 	"internal/poll"
 	"internal/testenv"
 	"io"
@@ -88,6 +90,9 @@ func TestDialTimeout(t *testing.T) {
 			if nerr, ok := err.(Error); !ok || !nerr.Timeout() {
 				t.Fatalf("#%d: %v", i, err)
 			}
+			if !errors.Is(err, oserror.ErrTimeout) {
+				t.Fatalf("#%d: Dial error is not os.ErrTimeout: %v", i, err)
+			}
 		}
 	}
 }
diff --git a/src/net/url/url.go b/src/net/url/url.go
index 5f40555bdc..9ff707b24e 100644
--- a/src/net/url/url.go
+++ b/src/net/url/url.go
@@ -13,6 +13,7 @@ package url
 import (
 	"errors"
 	"fmt"
+	"internal/oserror"
 	"sort"
 	"strconv"
 	"strings"
@@ -25,25 +26,10 @@ type Error struct {
 	Err error
 }
 
-func (e *Error) Error() string { return e.Op + " " + e.URL + ": " + e.Err.Error() }
-
-type timeout interface {
-	Timeout() bool
-}
-
-func (e *Error) Timeout() bool {
-	t, ok := e.Err.(timeout)
-	return ok && t.Timeout()
-}
-
-type temporary interface {
-	Temporary() bool
-}
-
-func (e *Error) Temporary() bool {
-	t, ok := e.Err.(temporary)
-	return ok && t.Temporary()
-}
+func (e *Error) Unwrap() error   { return e.Err }
+func (e *Error) Error() string   { return e.Op + " " + e.URL + ": " + e.Err.Error() }
+func (e *Error) Timeout() bool   { return oserror.IsTimeout(e.Err) }
+func (e *Error) Temporary() bool { return oserror.IsTemporary(e.Err) }
 
 func ishex(c byte) bool {
 	switch {
diff --git a/src/os/error.go b/src/os/error.go
index 4cf35f2b77..0c2e6a7322 100644
--- a/src/os/error.go
+++ b/src/os/error.go
@@ -23,6 +23,7 @@ var (
 	ErrNotExist   = errNotExist()   // "file does not exist"
 	ErrClosed     = errClosed()     // "file already closed"
 	ErrTimeout    = errTimeout()    // "deadline exceeded"
+	ErrTemporary  = errTemporary()  // "temporary error"
 	ErrNoDeadline = errNoDeadline() // "file type does not support deadline"
 )
 
@@ -32,6 +33,7 @@ func errExist() error      { return oserror.ErrExist }
 func errNotExist() error   { return oserror.ErrNotExist }
 func errClosed() error     { return oserror.ErrClosed }
 func errTimeout() error    { return oserror.ErrTimeout }
+func errTemporary() error  { return oserror.ErrTemporary }
 func errNoDeadline() error { return poll.ErrNoDeadline }
 
 type timeout interface {
diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
index 9a9265b667..17ef003eca 100644
--- a/src/os/exec/exec.go
+++ b/src/os/exec/exec.go
@@ -47,6 +47,8 @@ func (e *Error) Error() string {
 	return "exec: " + strconv.Quote(e.Name) + ": " + e.Err.Error()
 }
 
+func (e *Error) Unwrap() error { return e.Err }
+
 // Cmd represents an external command being prepared or run.
 //
 // A Cmd cannot be reused after calling its Run, Output or CombinedOutput
diff --git a/src/os/signal/internal/pty/pty.go b/src/os/signal/internal/pty/pty.go
index c1c7fcffc5..fb3ee1ea7a 100644
--- a/src/os/signal/internal/pty/pty.go
+++ b/src/os/signal/internal/pty/pty.go
@@ -38,6 +38,8 @@ func (e *PtyError) Error() string {
 	return fmt.Sprintf("%s: %s", e.FuncName, e.ErrorString)
 }
 
+func (e *PtyError) Unwrap() error { return e.Errno }
+
 // Open returns a master pty and the name of the linked slave tty.
 func Open() (master *os.File, slave string, err error) {
 	m, err := C.posix_openpt(C.O_RDWR)
diff --git a/src/text/template/exec.go b/src/text/template/exec.go
index 62cf19d30c..0e2ab0e211 100644
--- a/src/text/template/exec.go
+++ b/src/text/template/exec.go
@@ -121,6 +121,10 @@ func (e ExecError) Error() string {
 	return e.Err.Error()
 }
 
+func (e ExecError) Unwrap() error {
+	return e.Err
+}
+
 // errorf records an ExecError and terminates processing.
 func (s *state) errorf(format string, args ...interface{}) {
 	name := doublePercent(s.tmpl.Name())