net: make ErrClosed and ParseError implement net.Error

Fixes #45357

Change-Id: Iafd41fff232a89be4c88d4b1d66bc3c04d888bcc
Reviewed-on: https://go-review.googlesource.com/c/go/+/307030
Trust: Ian Lance Taylor <iant@golang.org>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

src/internal/poll/fd.go

@@ -13,11 +13,22 @@ import (
 	"errors"
 )
 
-// ErrNetClosing is returned when a network descriptor is used after
-// it has been closed. Keep this string consistent because of issue
-// #4373: since historically programs have not been able to detect
+// errNetClosing is the type of the variable ErrNetClosing.
+// This is used to implement the net.Error interface.
+type errNetClosing struct{}
+
+// Error returns the error message for ErrNetClosing.
+// Keep this string consistent because of issue #4373:
+// since historically programs have not been able to detect
 // this error, they look for the string.
-var ErrNetClosing = errors.New("use of closed network connection")
+func (e errNetClosing) Error() string { return "use of closed network connection" }
+
+func (e errNetClosing) Timeout() bool   { return false }
+func (e errNetClosing) Temporary() bool { return false }
+
+// ErrNetClosing is returned when a network descriptor is used after
+// it has been closed.
+var ErrNetClosing = errNetClosing{}
 
 // ErrFileClosing is returned when a file descriptor is used after it
 // has been closed.

src/net/net.go

@@ -539,6 +539,9 @@ type ParseError struct {
 
 func (e *ParseError) Error() string { return "invalid " + e.Type + ": " + e.Text }
 
+func (e *ParseError) Timeout() bool   { return false }
+func (e *ParseError) Temporary() bool { return false }
+
 type AddrError struct {
 	Err  string
 	Addr string
@@ -642,7 +645,7 @@ var errClosed = poll.ErrNetClosing
 // another goroutine before the I/O is completed. This may be wrapped
 // in another error, and should normally be tested using
 // errors.Is(err, net.ErrClosed).
-var ErrClosed = errClosed
+var ErrClosed error = errClosed
 
 type writerOnly struct {
 	io.Writer

src/net/net_test.go

@@ -588,3 +588,23 @@ func TestNotTemporaryRead(t *testing.T) {
 	}
 	withTCPConnPair(t, client, server)
 }
+
+// The various errors should implement the Error interface.
+func TestErrors(t *testing.T) {
+	var (
+		_ Error = &OpError{}
+		_ Error = &ParseError{}
+		_ Error = &AddrError{}
+		_ Error = UnknownNetworkError("")
+		_ Error = InvalidAddrError("")
+		_ Error = &timeoutError{}
+		_ Error = &DNSConfigError{}
+		_ Error = &DNSError{}
+	)
+
+	// ErrClosed was introduced as type error, so we can't check
+	// it using a declaration.
+	if _, ok := ErrClosed.(Error); !ok {
+		t.Fatal("ErrClosed does not implement Error")
+	}
+}