feat(service): support comma-separated values for host-to-IP mappings

cli/command/service/update.go

@@ -95,7 +95,7 @@ func newUpdateCommand(dockerCLI command.Cli) *cobra.Command {
 	flags.SetAnnotation(flagDNSOptionAdd, "version", []string{"1.25"})
 	flags.Var(&options.dnsSearch, flagDNSSearchAdd, "Add or update a custom DNS search domain")
 	flags.SetAnnotation(flagDNSSearchAdd, "version", []string{"1.25"})
-	flags.Var(&options.hosts, flagHostAdd, `Add a custom host-to-IP mapping ("host:ip")`)
+	flags.Var(opts.NewListOptsCSV(&options.hosts), flagHostAdd, `Add a custom host-to-IP mapping ("host:ip")`)
 	flags.SetAnnotation(flagHostAdd, "version", []string{"1.25"})
 	flags.BoolVar(&options.init, flagInit, false, "Use an init inside each service container to forward signals and reap processes")
 	flags.SetAnnotation(flagInit, "version", []string{"1.37"})
@@ -1235,7 +1235,7 @@ func updateHosts(flags *pflag.FlagSet, hosts *[]string) error {
 
 	// Append new hosts (in SwarmKit format)
 	if flags.Changed(flagHostAdd) {
-		values := convertExtraHostsToSwarmHosts(flags.Lookup(flagHostAdd).Value.(*opts.ListOpts).GetSlice())
+		values := convertExtraHostsToSwarmHosts(flags.Lookup(flagHostAdd).Value.(pflag.SliceValue).GetSlice())
 		newHosts = append(newHosts, values...)
 	}
 	*hosts = removeDuplicates(newHosts)

cli/command/service/update_test.go

@@ -388,6 +388,7 @@ func TestUpdateHealthcheckTable(t *testing.T) {
 
 func TestUpdateHosts(t *testing.T) {
 	flags := newUpdateCommand(nil).Flags()
+	flags.Set("host-add", "a:1.1.1.1,b:2.2.2.2")
 	flags.Set("host-add", "example.net:2.2.2.2")
 	flags.Set("host-add", "ipv6.net:2001:db8:abc8::1")
 	// adding the special "host-gateway" target should work
@@ -402,7 +403,7 @@ func TestUpdateHosts(t *testing.T) {
 	assert.ErrorContains(t, flags.Set("host-add", "$example.com$"), `bad format for add-host: "$example.com$"`)
 
 	hosts := []string{"1.2.3.4 example.com", "4.3.2.1 example.org", "2001:db8:abc8::1 example.net", "gateway.docker.internal:host-gateway"}
-	expected := []string{"1.2.3.4 example.com", "4.3.2.1 example.org", "2.2.2.2 example.net", "2001:db8:abc8::1 ipv6.net", "host-gateway host.docker.internal"}
+	expected := []string{"1.2.3.4 example.com", "4.3.2.1 example.org", "1.1.1.1 a", "2.2.2.2 b", "2.2.2.2 example.net", "2001:db8:abc8::1 ipv6.net", "host-gateway host.docker.internal"}
 
 	err := updateHosts(flags, &hosts)
 	assert.NilError(t, err)

docs/reference/commandline/service_update.md

@@ -39,7 +39,7 @@ Update a service
 | `--health-start-interval`                     | `duration`        |         | Time between running the check during the start period (ms\|s\|m\|h)                                |
 | `--health-start-period`                       | `duration`        |         | Start period for the container to initialize before counting retries towards unstable (ms\|s\|m\|h) |
 | `--health-timeout`                            | `duration`        |         | Maximum time to allow one check to run (ms\|s\|m\|h)                                                |
-| `--host-add`                                  | `list`            |         | Add a custom host-to-IP mapping (`host:ip`)                                                         |
+| `--host-add`                                  | `list`            |         | Add a custom host-to-IP mapping (`host:ip`). Multiple entries can be separated by comma |
 | `--host-rm`                                   | `list`            |         | Remove a custom host-to-IP mapping (`host:ip`) |
 | `--hostname`                                  | `string`          |         | Container hostname                                                                                  |
 | `--image`                                     | `string`          |         | Service image tag                                                                                   |

opts/opts.go

@@ -125,6 +125,51 @@ func (opts *ListOpts) WithValidator(validator ValidatorFctType) *ListOpts {
 	return opts
 }
 
+// ListOptsCSV wraps a ListOpts and implements [pflag.SliceValue], allowing
+// comma-separated values to be parsed in a single flag instance.
+//
+// Values passed to Set are split on commas before being validated using the
+// wrapped ListOpts' validator (for example, [ValidateExtraHost]).
+//
+// [pflag.SliceValue]: https://pkg.go.dev/github.com/spf13/pflag#SliceValue
+type ListOptsCSV struct{ *ListOpts }
+
+// NewListOptsCSV returns a new ListOptsCSV using the provided ListOpts.
+func NewListOptsCSV(opts *ListOpts) *ListOptsCSV {
+	return &ListOptsCSV{ListOpts: opts}
+}
+
+// Set splits the value on commas and validates each item using the wrapped
+// ListOpts.
+func (opts *ListOptsCSV) Set(value string) error {
+	for _, v := range strings.Split(value, ",") {
+		v = strings.TrimSpace(v)
+		if v == "" {
+			continue
+		}
+		if err := opts.ListOpts.Set(v); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Append implements pflag.SliceValue.
+func (opts *ListOptsCSV) Append(value string) error {
+	return opts.Set(value)
+}
+
+// Replace implements pflag.SliceValue.
+func (opts *ListOptsCSV) Replace(values []string) error {
+	*opts.ListOpts.values = (*opts.ListOpts.values)[:0]
+	for _, v := range values {
+		if err := opts.Set(v); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // MapOpts holds a map of values and a validation function.
 type MapOpts struct {
 	values    map[string]string