opts: preserve IPv6 zones in TCP addresses

cli/command/swarm/opts.go

@@ -5,6 +5,7 @@ import (
 	"encoding/pem"
 	"errors"
 	"fmt"
+	"net"
 	"os"
 	"strings"
 	"time"
@@ -74,7 +75,15 @@ func (*NodeAddrOption) Type() string {
 
 // Value returns the value of this option as addr:port
 func (a *NodeAddrOption) Value() string {
-	return strings.TrimPrefix(a.addr, "tcp://")
+	addr := strings.TrimPrefix(a.addr, "tcp://")
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		return addr
+	}
+	// ParseTCPAddr returns a URL-safe zone identifier, but net.Listen expects
+	// the raw percent sign in an IPv6 zone.
+	host = strings.ReplaceAll(host, "%25", "%")
+	return net.JoinHostPort(host, port)
 }
 
 // NewNodeAddrOption returns a new node address option

cli/command/swarm/opts_test.go

@@ -26,6 +26,12 @@ func TestNodeAddrOptionSetHostOnlyIPv6(t *testing.T) {
 	assert.Check(t, is.Equal("[::1]:2377", opt.Value()))
 }
 
+func TestNodeAddrOptionSetHostAndPortIPv6Zone(t *testing.T) {
+	opt := NewListenAddrOption()
+	assert.NilError(t, opt.Set("tcp://[fe80::1%25lo]:5555"))
+	assert.Check(t, is.Equal("[fe80::1%lo]:5555", opt.Value()))
+}
+
 func TestNodeAddrOptionSetPortOnly(t *testing.T) {
 	opt := NewListenAddrOption()
 	assert.NilError(t, opt.Set(":4545"))

opts/hosts.go

@@ -141,6 +141,10 @@ func ParseTCPAddr(tryAddr string, defaultAddr string) (string, error) {
 		return "", fmt.Errorf("invalid bind address format: %s", tryAddr)
 	}
 
+	// url.Parse unescapes the zone identifier in an IPv6 address. Re-escape
+	// its percent sign when formatting the address as a URL, otherwise the
+	// returned address cannot be parsed again.
+	host = strings.ReplaceAll(host, "%", "%25")
 	return fmt.Sprintf("tcp://%s%s", net.JoinHostPort(host, port), u.Path), nil
 }
 

opts/hosts_test.go

@@ -2,6 +2,7 @@ package opts
 
 import (
 	"net"
+	"net/url"
 	"testing"
 
 	"gotest.tools/v3/assert"
@@ -135,6 +136,16 @@ func TestParseTCP(t *testing.T) {
 	}
 }
 
+func TestParseTCPAddrIPv6Zone(t *testing.T) {
+	addr, err := ParseTCPAddr("tcp://[fe80::1%25lo]:5555", "tcp://127.0.0.1:2376")
+	assert.NilError(t, err)
+	assert.Check(t, is.Equal("tcp://[fe80::1%25lo]:5555", addr))
+
+	u, err := url.Parse(addr)
+	assert.NilError(t, err)
+	assert.Check(t, is.Equal("fe80::1%lo", u.Hostname()))
+}
+
 func TestParseInvalidUnixAddrInvalid(t *testing.T) {
 	if _, err := parseSimpleProtoAddr("unix", "tcp://127.0.0.1", "unix:///var/run/docker.sock"); err == nil || err.Error() != "invalid proto, expected unix: tcp://127.0.0.1" {
 		t.Fatalf("Expected an error, got %v", err)