Use errors.Is to compare against ErrClosedPipe.

I was still getting "io: read/write on closed pipe" errors in the logs,
even after comparing errors against io.ErrClosedPipe to skip logging
them. It turns out that kcp-go wraps many of its errors in another type.
The actual type of the errors was *errors.withStack, where errors is
https://github.com/pkg/errors. We can use the go1.13 errors interface
(https://blog.golang.org/go1.13-errors) to get at the value inside.

dnstt-client/main.go

@@ -26,6 +26,7 @@
 package main
 
 import (
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -95,7 +96,7 @@ func handle(local *net.TCPConn, sess *smux.Session, conv uint32) error {
 			// smux Stream.Write may return io.EOF.
 			err = nil
 		}
-		if err != nil && err != io.ErrClosedPipe {
+		if err != nil && !errors.Is(err, io.ErrClosedPipe) {
 			log.Printf("stream %08x:%d copy stream←local: %v", conv, stream.ID(), err)
 		}
 		local.CloseRead()
@@ -108,7 +109,7 @@ func handle(local *net.TCPConn, sess *smux.Session, conv uint32) error {
 			// smux Stream.WriteTo may return io.EOF.
 			err = nil
 		}
-		if err != nil && err != io.ErrClosedPipe {
+		if err != nil && !errors.Is(err, io.ErrClosedPipe) {
 			log.Printf("stream %08x:%d copy local←stream: %v", conv, stream.ID(), err)
 		}
 		local.CloseWrite()

dnstt-server/main.go

@@ -38,6 +38,7 @@ import (
 	"bytes"
 	"encoding/base32"
 	"encoding/binary"
+	"errors"
 	"flag"
 	"fmt"
 	"io"
@@ -205,7 +206,7 @@ func handleStream(stream *smux.Stream, upstream string, conv uint32) error {
 			// smux Stream.Write may return io.EOF.
 			err = nil
 		}
-		if err != nil && err != io.ErrClosedPipe {
+		if err != nil && !errors.Is(err, io.ErrClosedPipe) {
 			log.Printf("stream %08x:%d copy stream←upstream: %v", conv, stream.ID(), err)
 		}
 		upstreamTCPConn.CloseRead()
@@ -218,7 +219,7 @@ func handleStream(stream *smux.Stream, upstream string, conv uint32) error {
 			// smux Stream.WriteTo may return io.EOF.
 			err = nil
 		}
-		if err != nil && err != io.ErrClosedPipe {
+		if err != nil && !errors.Is(err, io.ErrClosedPipe) {
 			log.Printf("stream %08x:%d copy upstream←stream: %v", conv, stream.ID(), err)
 		}
 		upstreamTCPConn.CloseWrite()
@@ -302,11 +303,7 @@ func acceptSessions(ln *kcp.Listener, privkey []byte, mtu int, upstream string)
 				conn.Close()
 			}()
 			err := acceptStreams(conn, privkey, upstream)
-			if err == io.ErrClosedPipe {
-				// We don't want to report this error.
-				err = nil
-			}
-			if err != nil {
+			if err != nil && !errors.Is(err, io.ErrClosedPipe) {
 				log.Printf("session %08x acceptStreams: %v", conn.GetConv(), err)
 			}
 		}()

go.mod

@@ -1,6 +1,6 @@
 module www.bamsoftware.com/git/dnstt.git
 
-go 1.11
+go 1.13
 
 require (
 	github.com/flynn/noise v1.0.0