Add stack config command

Make use of existing modules and functions in order to output the merged configs.
Added skip interpolation flag of variables, so that you can pipe the output back to stack deploy without much hassle.

Signed-off-by: Stoica-Marcu Floris-Andrei <floris.sm@gmail.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/stack/cmd.go

@@ -33,6 +33,7 @@ func NewStackCommand(dockerCli command.Cli) *cobra.Command {
 		newPsCommand(dockerCli),
 		newRemoveCommand(dockerCli),
 		newServicesCommand(dockerCli),
+		newConfigCommand(dockerCli),
 	)
 	flags := cmd.PersistentFlags()
 	flags.String("orchestrator", "", "Orchestrator to use (swarm|all)")

cli/command/stack/config.go

@@ -0,0 +1,60 @@
+package stack
+
+import (
+	"fmt"
+
+	"github.com/docker/cli/cli"
+	"github.com/docker/cli/cli/command"
+	"github.com/docker/cli/cli/command/stack/loader"
+	"github.com/docker/cli/cli/command/stack/options"
+	composeLoader "github.com/docker/cli/cli/compose/loader"
+	composetypes "github.com/docker/cli/cli/compose/types"
+	"github.com/spf13/cobra"
+	yaml "gopkg.in/yaml.v2"
+)
+
+func newConfigCommand(dockerCli command.Cli) *cobra.Command {
+	var opts options.Config
+
+	cmd := &cobra.Command{
+		Use:   "config [OPTIONS]",
+		Short: "Outputs the final config file, after doing merges and interpolations",
+		Args:  cli.NoArgs,
+		RunE: func(cmd *cobra.Command, args []string) error {
+			configDetails, err := loader.GetConfigDetails(opts.Composefiles, dockerCli.In())
+			if err != nil {
+				return err
+			}
+
+			cfg, err := outputConfig(configDetails, opts.SkipInterpolation)
+			if err != nil {
+				return err
+			}
+
+			_, err = fmt.Fprintf(dockerCli.Out(), "%s", cfg)
+			return err
+		},
+	}
+
+	flags := cmd.Flags()
+	flags.StringSliceVarP(&opts.Composefiles, "compose-file", "c", []string{}, `Path to a Compose file, or "-" to read from stdin`)
+	flags.BoolVar(&opts.SkipInterpolation, "skip-interpolation", false, "Skip interpolation and output only merged config")
+	return cmd
+}
+
+// outputConfig returns the merged and interpolated config file
+func outputConfig(configFiles composetypes.ConfigDetails, skipInterpolation bool) (string, error) {
+	optsFunc := func(options *composeLoader.Options) {
+		options.SkipInterpolation = skipInterpolation
+	}
+	config, err := composeLoader.Load(configFiles, optsFunc)
+	if err != nil {
+		return "", err
+	}
+
+	d, err := yaml.Marshal(&config)
+	if err != nil {
+		return "", err
+	}
+	return string(d), nil
+}

cli/command/stack/config_test.go

@@ -0,0 +1,106 @@
+package stack
+
+import (
+	"io"
+	"testing"
+
+	"github.com/docker/cli/cli/compose/loader"
+	composetypes "github.com/docker/cli/cli/compose/types"
+	"github.com/docker/cli/internal/test"
+	"gotest.tools/v3/assert"
+)
+
+func TestConfigWithEmptyComposeFile(t *testing.T) {
+	cmd := newConfigCommand(test.NewFakeCli(&fakeClient{}))
+	cmd.SetOut(io.Discard)
+
+	assert.ErrorContains(t, cmd.Execute(), `Please specify a Compose file`)
+}
+
+var configMergeTests = []struct {
+	name              string
+	skipInterpolation bool
+	first             string
+	second            string
+	merged            string
+}{
+	{
+		name:              "With Interpolation",
+		skipInterpolation: false,
+		first: `version: "3.7"
+services:
+  foo:
+    image: busybox:latest
+    command: cat file1.txt
+`,
+		second: `version: "3.7"
+services:
+  foo:
+    image: busybox:${VERSION}
+    command: cat file2.txt
+`,
+		merged: `version: "3.7"
+services:
+  foo:
+    command:
+    - cat
+    - file2.txt
+    image: busybox:1.0
+`,
+	},
+	{
+		name:              "Without Interpolation",
+		skipInterpolation: true,
+		first: `version: "3.7"
+services:
+  foo:
+    image: busybox:latest
+    command: cat file1.txt
+`,
+		second: `version: "3.7"
+services:
+  foo:
+    image: busybox:${VERSION}
+    command: cat file2.txt
+`,
+		merged: `version: "3.7"
+services:
+  foo:
+    command:
+    - cat
+    - file2.txt
+    image: busybox:${VERSION}
+`,
+	},
+}
+
+func TestConfigMergeInterpolation(t *testing.T) {
+
+	for _, tt := range configMergeTests {
+		t.Run(tt.name, func(t *testing.T) {
+			firstConfig := []byte(tt.first)
+			secondConfig := []byte(tt.second)
+
+			firstConfigData, err := loader.ParseYAML(firstConfig)
+			assert.NilError(t, err)
+			secondConfigData, err := loader.ParseYAML(secondConfig)
+			assert.NilError(t, err)
+
+			env := map[string]string{
+				"VERSION": "1.0",
+			}
+
+			cfg, err := outputConfig(composetypes.ConfigDetails{
+				ConfigFiles: []composetypes.ConfigFile{
+					{Config: firstConfigData, Filename: "firstConfig"},
+					{Config: secondConfigData, Filename: "secondConfig"},
+				},
+				Environment: env,
+			}, tt.skipInterpolation)
+			assert.NilError(t, err)
+
+			assert.Equal(t, cfg, tt.merged)
+		})
+	}
+
+}

cli/command/stack/loader/loader.go

@@ -18,7 +18,7 @@ import (
 
 // LoadComposefile parse the composefile specified in the cli and returns its Config and version.
 func LoadComposefile(dockerCli command.Cli, opts options.Deploy) (*composetypes.Config, error) {
-	configDetails, err := getConfigDetails(opts.Composefiles, dockerCli.In())
+	configDetails, err := GetConfigDetails(opts.Composefiles, dockerCli.In())
 	if err != nil {
 		return nil, err
 	}
@@ -68,7 +68,8 @@ func propertyWarnings(properties map[string]string) string {
 	return strings.Join(msgs, "\n\n")
 }
 
-func getConfigDetails(composefiles []string, stdin io.Reader) (composetypes.ConfigDetails, error) {
+// GetConfigDetails parse the composefiles specified in the cli and returns their ConfigDetails
+func GetConfigDetails(composefiles []string, stdin io.Reader) (composetypes.ConfigDetails, error) {
 	var details composetypes.ConfigDetails
 
 	if len(composefiles) == 0 {

cli/command/stack/loader/loader_test.go

@@ -21,7 +21,7 @@ services:
 	file := fs.NewFile(t, "test-get-config-details", fs.WithContent(content))
 	defer file.Remove()
 
-	details, err := getConfigDetails([]string{file.Path()}, nil)
+	details, err := GetConfigDetails([]string{file.Path()}, nil)
 	assert.NilError(t, err)
 	assert.Check(t, is.Equal(filepath.Dir(file.Path()), details.WorkingDir))
 	assert.Assert(t, is.Len(details.ConfigFiles, 1))
@@ -36,7 +36,7 @@ services:
   foo:
     image: alpine:3.5
 `
-	details, err := getConfigDetails([]string{"-"}, strings.NewReader(content))
+	details, err := GetConfigDetails([]string{"-"}, strings.NewReader(content))
 	assert.NilError(t, err)
 	cwd, err := os.Getwd()
 	assert.NilError(t, err)

cli/command/stack/options/opts.go

@@ -11,6 +11,12 @@ type Deploy struct {
 	Prune            bool
 }
 
+// Config holds docker stack config options
+type Config struct {
+	Composefiles      []string
+	SkipInterpolation bool
+}
+
 // List holds docker stack ls options
 type List struct {
 	Format        string

docs/reference/commandline/index.md

@@ -153,12 +153,13 @@ read the [`dockerd`](dockerd.md) reference page.
 ### Swarm stack commands
 
 | Command                             | Description                                             |
-|:------------------------------------|:-----------------------------------------------|
+|:------------------------------------|:--------------------------------------------------------|
 | [stack deploy](stack_deploy.md)     | Deploy a new stack or update an existing stack          |
 | [stack ls](stack_ls.md)             | List stacks in the swarm                                |
 | [stack ps](stack_ps.md)             | List the tasks in the stack                             |
 | [stack rm](stack_rm.md)             | Remove the stack from the swarm                         |
 | [stack services](stack_services.md) | List the services in the stack                          |
+| [stack config](stack_config.md)     | Output the Compose file after merges and interpolations |
 
 ### Plugin commands
 

docs/reference/commandline/stack_config.md

@@ -0,0 +1,68 @@
+---
+title: "stack config"
+description: "The stack config command description and usage"
+keywords: "stack, config"
+---
+
+# stack config
+
+```markdown
+Usage:	docker stack config [OPTIONS]
+
+Outputs the final config file, after doing merges and interpolations
+
+Aliases:
+  config, cfg
+
+Options:
+  -c, --compose-file strings   Path to a Compose file, or "-" to read from stdin
+      --orchestrator string    Orchestrator to use (swarm|kubernetes|all)
+      --skip-interpolation     Skip interpolation and output only merged config
+```
+
+## Description
+
+Outputs the final Compose file, after doing the merges and interpolations of the input Compose files.
+
+## Examples
+
+The following command outputs the result of the merge and interpolation of two Compose files.
+
+```bash
+$ docker stack config --compose-file docker-compose.yml --compose-file docker-compose.prod.yml
+```
+
+The Compose file can also be provided as standard input with `--compose-file -`:
+
+```bash
+$ cat docker-compose.yml | docker stack config --compose-file -
+```
+
+### Skipping interpolation
+
+In some cases, it might be useful to skip interpolation of environment variables.
+For example, when you want to pipe the output of this command back to `stack deploy`.
+
+If you have a regex for a redirect route in an environment variable for your webserver you would use two `$` signs to prevent `stack deploy` from interpolating `${1}`.
+
+```bash
+  service: webserver
+  environment:
+    REDIRECT_REGEX=http://host/redirect/$${1} 
+```
+
+With interpolation, the `stack config` command will replace the environment variable in the Compose file 
+with `REDIRECT_REGEX=http://host/redirect/${1}`, but then when piping it back to the `stack deploy` 
+command it will be interpolated again and result in undefined behavior. 
+That is why, when piping the output back to `stack deploy` one should always prefer the `--skip-interpolation` option.
+
+```
+$ docker stack config --compose-file web.yml --compose-file web.prod.yml --skip-interpolation | docker stack deploy --compose-file -
+```
+
+## Related commands
+
+* [stack deploy](stack_deploy.md)
+* [stack ps](stack_ps.md)
+* [stack rm](stack_rm.md)
+* [stack services](stack_services.md)

docs/reference/commandline/stack_deploy.md

@@ -111,3 +111,4 @@ axqh55ipl40h  vossibility_vossibility-collector  replicated  1/1       icecrime/
 * [stack ps](stack_ps.md)
 * [stack rm](stack_rm.md)
 * [stack services](stack_services.md)
+* [stack config](stack_config.md)

e2e/stack/config_test.go

@@ -0,0 +1,12 @@
+package stack
+
+import (
+	"testing"
+
+	"gotest.tools/v3/icmd"
+)
+
+func TestConfigFullStack(t *testing.T) {
+	result := icmd.RunCommand("docker", "stack", "config", "--compose-file=./testdata/full-stack.yml")
+	result.Assert(t, icmd.Success)
+}