fix(port): preserve tie order for dual-stack port publishers

cmd/compose/port.go

@@ -19,7 +19,6 @@ package compose
 import (
 	"context"
 	"fmt"
-	"net"
 	"strconv"
 	"strings"
 
@@ -86,9 +85,8 @@ func runPort(ctx context.Context, dockerCli command.Cli, backendOptions *Backend
 		return err
 	}
 
-	if opts.port != 0 && len(publishers) > 0 {
-		p := publishers[0]
-		_, _ = fmt.Fprintf(dockerCli.Out(), "%s\n", net.JoinHostPort(p.URL, strconv.Itoa(p.PublishedPort)))
+	if opts.port != 0 {
+		_, _ = fmt.Fprintf(dockerCli.Out(), "%s\n", publishers[0].HostPort())
 		return nil
 	}
 	for _, p := range publishers {

pkg/api/api.go

@@ -609,7 +609,12 @@ type PortPublisher struct {
 }
 
 func (p PortPublisher) String() string {
-	return fmt.Sprintf("%d/%s -> %s", p.TargetPort, p.Protocol, net.JoinHostPort(p.URL, strconv.Itoa(p.PublishedPort)))
+	return fmt.Sprintf("%d/%s -> %s", p.TargetPort, p.Protocol, p.HostPort())
+}
+
+// HostPort renders the host-side address the port is published on
+func (p PortPublisher) HostPort() string {
+	return net.JoinHostPort(p.URL, strconv.Itoa(p.PublishedPort))
 }
 
 // ContainerSummary hold high-level description of a container

pkg/compose/port_test.go

@@ -0,0 +1,146 @@
+/*
+   Copyright 2020 Docker Compose CLI authors
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package compose
+
+import (
+	"net/netip"
+	"strings"
+	"testing"
+
+	"github.com/moby/moby/api/types/container"
+	"github.com/moby/moby/client"
+	"go.uber.org/mock/gomock"
+	"gotest.tools/v3/assert"
+
+	compose "github.com/docker/compose/v5/pkg/api"
+)
+
+func TestPorts(t *testing.T) {
+	const service = "web"
+
+	ports := []container.PortSummary{
+		{IP: netip.MustParseAddr("0.0.0.0"), PrivatePort: 80, PublicPort: 8080, Type: "tcp"},
+		{IP: netip.MustParseAddr("::"), PrivatePort: 80, PublicPort: 8080, Type: "tcp"},
+		{PrivatePort: 53, PublicPort: 5353, Type: "udp"},
+		{PrivatePort: 3000, Type: "tcp"}, // exposed but not published: no host IP/port
+	}
+
+	tests := []struct {
+		name     string
+		port     uint16
+		protocol string
+		want     compose.PortPublishers
+		wantErr  string
+	}{
+		{
+			name: "no port and no protocol lists every mapping",
+			want: compose.PortPublishers{
+				{TargetPort: 53, PublishedPort: 5353, Protocol: "udp"},
+				{URL: "0.0.0.0", TargetPort: 80, PublishedPort: 8080, Protocol: "tcp"},
+				{URL: "::", TargetPort: 80, PublishedPort: 8080, Protocol: "tcp"},
+				{TargetPort: 3000, Protocol: "tcp"},
+			},
+		},
+		{
+			name:     "protocol filters the list without a port",
+			protocol: "udp",
+			want: compose.PortPublishers{
+				{TargetPort: 53, PublishedPort: 5353, Protocol: "udp"},
+			},
+		},
+		{
+			name:     "port and protocol match every dual-stack mapping for that port",
+			port:     80,
+			protocol: "tcp",
+			want: compose.PortPublishers{
+				{URL: "0.0.0.0", TargetPort: 80, PublishedPort: 8080, Protocol: "tcp"},
+				{URL: "::", TargetPort: 80, PublishedPort: 8080, Protocol: "tcp"},
+			},
+		},
+		{
+			name:     "unmatched port returns an error naming the container",
+			port:     9999,
+			protocol: "tcp",
+			wantErr:  "no port 9999/tcp for container 123",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockCtrl := gomock.NewController(t)
+			defer mockCtrl.Finish()
+
+			api, cli := prepareMocks(mockCtrl)
+			tested, err := NewComposeService(cli)
+			assert.NilError(t, err)
+
+			projectName := strings.ToLower(testProject)
+			ctr := testContainer(service, "123", false)
+			ctr.Ports = append([]container.PortSummary(nil), ports...)
+
+			api.EXPECT().ContainerList(t.Context(), client.ContainerListOptions{
+				Filters: projectFilter(projectName).Add("label", serviceFilter(service), compose.ConfigHashLabel),
+			}).Return(client.ContainerListResult{Items: []container.Summary{ctr}}, nil)
+
+			got, err := tested.Ports(t.Context(), projectName, service, tt.port, compose.PortOptions{Protocol: tt.protocol})
+			if tt.wantErr != "" {
+				assert.ErrorContains(t, err, tt.wantErr)
+				return
+			}
+			assert.NilError(t, err)
+			assert.DeepEqual(t, got, tt.want)
+		})
+	}
+}
+
+// TestContainerPublishersPreservesTieOrder guards against containerPublishers
+// reordering same-PrivatePort entries (e.g. a dual-stack publish exposing the
+// same target port on both an IPv4 and an IPv6 host address): Ports() picks
+// publishers[0] as *the* answer for a single-port lookup, so a sort that
+// merely orders by PrivatePort must not additionally scramble ties.
+//
+// sort.Slice's pdqsort falls back to a (stable) insertion sort for slices of
+// <=12 elements, so a small fixture can't tell a stable sort from an unstable
+// one; this uses enough tied groups to force the quicksort partitioning path.
+func TestContainerPublishersPreservesTieOrder(t *testing.T) {
+	var ports []container.PortSummary
+	privatePorts := []int{80, 53, 443}
+	for _, pp := range privatePorts {
+		for i := range 5 {
+			ports = append(ports, container.PortSummary{
+				PrivatePort: uint16(pp),
+				PublicPort:  uint16(i), // tags each tied entry with its input position
+				Type:        "tcp",
+			})
+		}
+	}
+	ports = append(ports, container.PortSummary{PrivatePort: 22, PublicPort: 0, Type: "tcp"})
+
+	ctr := testContainer("web", "123", false)
+	ctr.Ports = ports
+
+	got := containerPublishers(ctr)
+
+	lastPosByTargetPort := map[int]int{}
+	for _, p := range got {
+		pos := p.PublishedPort
+		if prev, ok := lastPosByTargetPort[p.TargetPort]; ok {
+			assert.Assert(t, pos > prev, "tied entries for private port %d out of input order: got position %d after %d", p.TargetPort, pos, prev)
+		}
+		lastPosByTargetPort[p.TargetPort] = pos
+	}
+}

pkg/compose/ps.go

@@ -87,7 +87,7 @@ func (s *composeService) containerSummary(ctx context.Context, ctr container.Sum
 }
 
 func containerPublishers(ctr container.Summary) []api.PortPublisher {
-	sort.Slice(ctr.Ports, func(i, j int) bool {
+	sort.SliceStable(ctr.Ports, func(i, j int) bool {
 		return ctr.Ports[i].PrivatePort < ctr.Ports[j].PrivatePort
 	})
 	publishers := make([]api.PortPublisher, len(ctr.Ports))