example provider implementation

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

docs/examples/provider.go

@@ -0,0 +1,74 @@
+/*
+   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 main
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/spf13/cobra"
+)
+
+func main() {
+	cmd := &cobra.Command{
+		Short: "Compose Provider Example",
+		Use:   "demo",
+	}
+	cmd.AddCommand(composeCommand())
+	err := cmd.Execute()
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func composeCommand() *cobra.Command {
+	c := &cobra.Command{
+		Use:              "compose EVENT",
+		TraverseChildren: true,
+	}
+	c.PersistentFlags().String("project-name", "", "compose project name") // unused
+	c.AddCommand(&cobra.Command{
+		Use:  "up",
+		Run:  up,
+		Args: cobra.ExactArgs(1),
+	})
+	c.AddCommand(&cobra.Command{
+		Use:  "down",
+		Run:  down,
+		Args: cobra.ExactArgs(1),
+	})
+	return c
+}
+
+const lineSeparator = "\n"
+
+func up(_ *cobra.Command, args []string) {
+	servicename := args[0]
+	fmt.Printf(`{ "type": "debug", "message": "Starting %s" }%s`, servicename, lineSeparator)
+
+	for i := 0; i < 100; i += 10 {
+		time.Sleep(1 * time.Second)
+		fmt.Printf(`{ "type": "info", "message": "Processing ... %d%%" }%s`, i, lineSeparator)
+	}
+	fmt.Printf(`{ "type": "setenv", "message": "URL=https://magic.cloud/%s" }%s`, servicename, lineSeparator)
+}
+
+func down(_ *cobra.Command, _ []string) {
+	fmt.Printf(`{ "type": "error", "message": "Permission error" }%s`, lineSeparator)
+}

docs/extension.md

@@ -104,4 +104,8 @@ into its runtime environment.
 ## Down lifecycle
 
 `down` lifecycle is equivalent to `up` with the `<provider> compose --project-name <NAME> down <SERVICE>` command.
-The provider is responsible for releasing all resources associated with the service. 
+The provider is responsible for releasing all resources associated with the service. 
+
+## Examples
+
+See [example](examples/provider.go) for illustration on implementing this API in a command line