Add dependencies and restart policy to s6 services

pkg/build/types/schema.json

@@ -199,15 +199,39 @@
           "description": "Optional: The shell fragment of the entrypoint command"
         },
         "services": {
-          "additionalProperties": {
+          "$ref": "#/$defs/ImageServices"
+        }
+      },
+      "additionalProperties": false,
+      "type": "object"
+    },
+    "ImageService": {
+      "properties": {
+        "command": {
+          "type": "string",
+          "description": "Required: The command of the service"
+        },
+        "depends_on": {
+          "items": {
             "type": "string"
           },
-          "type": "object"
+          "type": "array",
+          "description": "Optional: The name of the parent service"
+        },
+        "restart": {
+          "type": "string",
+          "description": "Optional: The restart policy of the service ('always' by default as in docker)"
         }
       },
       "additionalProperties": false,
       "type": "object"
     },
+    "ImageServices": {
+      "additionalProperties": {
+        "$ref": "#/$defs/ImageService"
+      },
+      "type": "object"
+    },
     "Layering": {
       "properties": {
         "strategy": {

pkg/build/types/types.go

@@ -21,6 +21,7 @@ import (
 	"sort"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
+	"gopkg.in/yaml.v3"
 )
 
 type User struct {
@@ -130,6 +131,17 @@ func (i ImageContents) MarshalYAML() (interface{}, error) {
 	return ri, nil
 }
 
+type ImageService struct {
+	// Required: The command of the service
+	Command string `json:"command,omitempty" yaml:"command"`
+	// Optional: The name of the parent service
+	DependsOn []string `json:"depends_on,omitempty" yaml:"depends_on"`
+	// Optional: The restart policy of the service ('always' by default as in docker)
+	Restart string `json:"restart,omitempty" yaml:"restart"`
+}
+
+type ImageServices map[string]ImageService
+
 type ImageEntrypoint struct {
 	// Optional: The type of entrypoint. Only "service-bundle" is supported.
 	Type string `json:"type,omitempty"`
@@ -138,7 +150,33 @@ type ImageEntrypoint struct {
 	// Optional: The shell fragment of the entrypoint command
 	ShellFragment string `json:"shell-fragment,omitempty" yaml:"shell-fragment"`
 
-	Services map[string]string `json:"services,omitempty"`
+	Services ImageServices `json:"services,omitempty"`
+}
+
+func (s *ImageServices) UnmarshalYAML(value *yaml.Node) error {
+	// First attempt to parse as map[string]ImageService
+	var structured map[string]ImageService
+	if err := value.Decode(&structured); err == nil {
+		*s = structured
+		return nil
+	}
+
+	// If err, attempt as map[string]string
+	var flat map[string]string
+	if err := value.Decode(&flat); err == nil {
+		converted := make(map[string]ImageService)
+		for name, cmd := range flat {
+			converted[name] = ImageService{
+				Command:   cmd,
+				DependsOn: []string{},
+				Restart:   "always",
+			}
+		}
+		*s = converted
+		return nil
+	}
+
+	return fmt.Errorf("services field must be map[string]string or map[string]ImageService")
 }
 
 type ImageAccounts struct {

pkg/s6/s6.go

@@ -18,8 +18,6 @@ import (
 	apkfs "chainguard.dev/apko/pkg/apk/fs"
 )
 
-type Services map[string]string
-
 type Context struct {
 	fs apkfs.FullFS
 }

pkg/s6/supervision_tree.go

@@ -18,11 +18,13 @@ import (
 	"context"
 	"fmt"
 	"path/filepath"
+	"strings"
 
+	apkbuildtypes "chainguard.dev/apko/pkg/build/types"
 	"github.com/chainguard-dev/clog"
 )
 
-func (sc *Context) WriteSupervisionTree(ctx context.Context, services Services) error {
+func (sc *Context) WriteSupervisionTree(ctx context.Context, services apkbuildtypes.ImageServices) error {
 	log := clog.FromContext(ctx)
 	log.Debug("generating supervision tree")
 
@@ -33,9 +35,39 @@ func (sc *Context) WriteSupervisionTree(ctx context.Context, services Services)
 			return fmt.Errorf("could not make supervision directory: %w", err)
 		}
 
-		if err := sc.fs.WriteFile(filepath.Join(svcdir, "run"), []byte(fmt.Sprintf("#!/bin/execlineb\n%s\n", svccmd)), 0755); err != nil {
+		// Construct dependencies by adding 's6-svwait' if needed, then execute the main command
+		runContent := "#!/bin/execlineb\n"
+		for _, dep := range svccmd.DependsOn {
+			runContent += fmt.Sprintf("foreground { s6-svwait -D /sv/%s }\n", dep)
+		}
+		runContent += svccmd.Command
+
+		if err := sc.fs.WriteFile(filepath.Join(svcdir, "run"), []byte(runContent), 0755); err != nil {
 			return fmt.Errorf("could not write runfile: %w", err)
 		}
+
+		// Manage finish scripts according to defined restart policy
+		restartPolicy := strings.ToLower(strings.TrimSpace(svccmd.Restart))
+
+		var finishContent string
+		switch restartPolicy {
+		case "no":
+			// Always send down signal
+			finishContent = fmt.Sprintf(`#!/bin/execlineb
+			s6-svc -D /sv/%s`, service)
+		case "on-failure":
+			// Send down signal in case the run script exited with zero value
+			finishContent = fmt.Sprintf(`#!/bin/execlineb -s1
+			if { eltest ${1} -eq 0 }
+			s6-svc -D /sv/%s
+			`, service)
+		}
+
+		if finishContent != "" {
+			if err := sc.fs.WriteFile(filepath.Join(svcdir, "finish"), []byte(finishContent), 0755); err != nil {
+				return fmt.Errorf("could not write finishfile: %w", err)
+			}
+		}
 	}
 
 	return nil