cli: Load config file and add config subcommand.

Signed-off-by: Ruben Jenster <r.jenster@drachenfels.de>

cmd/lxcri/cli.go

@@ -15,6 +15,7 @@ import (
 	"github.com/lxc/lxcri/pkg/specki"
 	"github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/urfave/cli/v2"
+	"sigs.k8s.io/yaml"
 )
 
 var (
@@ -118,6 +119,24 @@ func (app *app) releaseLog() error {
 	return nil
 }
 
+func loadConfig() error {
+	clxc.configFile = defaultConfigFile
+	if val, ok := os.LookupEnv("LXCRI_CONFIG"); ok {
+		clxc.configFile = val
+	}
+
+	data, err := os.ReadFile(clxc.configFile)
+	// Don't fail if the default config file does not exist.
+	if os.IsNotExist(err) && clxc.configFile == defaultConfigFile {
+		return nil
+	}
+	if err != nil {
+		return err
+	}
+
+	return yaml.Unmarshal(data, &clxc)
+}
+
 func main() {
 	app := cli.NewApp()
 	app.Name = "lxcri"
@@ -137,7 +156,12 @@ func main() {
 		&execCmd,
 		&inspectCmd,
 		&listCmd,
-		// TODO extend urfave/cli to render a default environment file.
+		&configCmd,
+	}
+
+	err := loadConfig()
+	if err != nil {
+		panic(fmt.Errorf("failed to read config file: %w", err))
 	}
 
 	app.Flags = []cli.Flag{
@@ -815,3 +839,53 @@ func inspectContainer(id string, t *template.Template) error {
 	_, err = fmt.Fprint(os.Stdout, string(j))
 	return err
 }
+
+var configCmd = cli.Command{
+	Name:   "config",
+	Usage:  "Output a config file for lxcri. Global options modify the output.",
+	Action: doConfig,
+	Flags: []cli.Flag{
+		&cli.StringFlag{
+			Name:  "out",
+			Usage: "write config to file",
+		},
+		&cli.BoolFlag{
+			Name:  "default",
+			Usage: "use the builtin default configuration",
+		},
+		&cli.BoolFlag{
+			Name:  "update-current",
+			Usage: "write to the current config file (--out is ignored)",
+		},
+		&cli.BoolFlag{
+			Name:  "quiet",
+			Usage: "do not print config to stdout",
+		},
+	},
+}
+
+// NOTE lxcri config  > /etc/lxcri/lxcri.yaml does not work
+func doConfig(ctxcli *cli.Context) (err error) {
+	// generate yaml
+	c := clxc
+	if ctxcli.Bool("default") {
+		c = defaultApp
+	}
+	data, err := yaml.Marshal(c)
+	if err != nil {
+		return err
+	}
+	if !ctxcli.Bool("quiet") {
+		fmt.Printf("---\n%s---\n", string(data))
+	}
+
+	out := ctxcli.String("out")
+	if ctxcli.Bool("update-current") {
+		out = clxc.configFile
+	}
+	if out != "" {
+		fmt.Printf("Writing to file %s\n", out)
+		return os.WriteFile(out, data, 0640)
+	}
+	return nil
+}

go.mod

@@ -3,7 +3,6 @@ module github.com/lxc/lxcri
 require (
 	github.com/cpuguy83/go-md2man/v2 v2.0.0 // indirect
 	github.com/creack/pty v1.1.11
-	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/drachenfels-de/gocapability v0.0.0-20210413092208-755d79b01352
 	github.com/kr/pretty v0.2.1 // indirect
 	github.com/opencontainers/runtime-spec v1.0.3-0.20200929063507-e6143ca7d51d
@@ -13,6 +12,7 @@ require (
 	golang.org/x/sys v0.0.0-20210228012217-479acdf4ea46
 	gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15 // indirect
 	gopkg.in/lxc/go-lxc.v2 v2.0.0-20210205143421-c4b883be4881
+	sigs.k8s.io/yaml v1.2.0
 )
 
 replace golang.org/x/crypto => golang.org/x/crypto v0.0.0-20201221181555-eec23a3978ad

go.sum

@@ -51,5 +51,9 @@ gopkg.in/check.v1 v1.0.0-20190902080502-41f04d3bba15/go.mod h1:Co6ibVJAznAaIkqp8
 gopkg.in/lxc/go-lxc.v2 v2.0.0-20210205143421-c4b883be4881 h1:YcCjv1g/OoEJ93hK3p+5MhPyuIMD9FwOYF5f4D7rNKk=
 gopkg.in/lxc/go-lxc.v2 v2.0.0-20210205143421-c4b883be4881/go.mod h1:4K0lbUXeslpmjwJZyW1lI6s5j97mrsj4+kpYwwvuLXo=
 gopkg.in/yaml.v2 v2.2.3/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
+gopkg.in/yaml.v2 v2.2.8 h1:obN1ZagJSUGI0Ek/LBmuj4SNLPfIny3KsKFopxRdj10=
+gopkg.in/yaml.v2 v2.2.8/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
 gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+sigs.k8s.io/yaml v1.2.0 h1:kr/MCeFWJWTwyaHoR9c8EjH9OumOmoF9YGiZd7lFm/Q=
+sigs.k8s.io/yaml v1.2.0/go.mod h1:yfXDCHCao9+ENCvLSE62v9VSji2MKu5jeNfTrofGhJc=