feat(config): add config command to view and set broker configuration

cmd/imds-broker/config.go

@@ -0,0 +1,117 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/urfave/cli/v3"
+
+	brokerconfig "github.com/jamestelfer/imds-broker/pkg/config"
+)
+
+// configCommand defines the host-side configuration command. It reads and
+// writes the broker configuration file directly; it makes no AWS calls and
+// starts no servers. The configuration file is host-controlled, not an
+// agent-reachable interface: see the project README sandbox model.
+func configCommand() *cli.Command {
+	return &cli.Command{
+		Name:  "config",
+		Usage: "Inspect and modify the host-side broker configuration file",
+		Commands: []*cli.Command{
+			configPathCommand(),
+			configListCommand(),
+			configSetCommand(),
+		},
+	}
+}
+
+// commandWriter returns the root command writer, defaulting to stdout.
+func commandWriter(cmd *cli.Command) io.Writer {
+	if w := cmd.Root().Writer; w != nil {
+		return w
+	}
+	return os.Stdout
+}
+
+func configPathCommand() *cli.Command {
+	return &cli.Command{
+		Name:  "path",
+		Usage: "Print the configuration file location",
+		Action: func(ctx context.Context, cmd *cli.Command) error {
+			path, err := brokerconfig.ResolvePath(ctx)
+			if err != nil {
+				return fmt.Errorf("config path: %w", err)
+			}
+			_, err = io.WriteString(commandWriter(cmd), path+"\n")
+			return err
+		},
+	}
+}
+
+func configListCommand() *cli.Command {
+	return &cli.Command{
+		Name:    "list",
+		Aliases: []string{"show"},
+		Usage:   "List the current configuration values",
+		Action: func(ctx context.Context, cmd *cli.Command) error {
+			cfg, err := brokerconfig.Load(ctx)
+			if err != nil {
+				return fmt.Errorf("config list: %w", err)
+			}
+
+			fileState := "not found (using built-in defaults)"
+			if cfg.Found {
+				fileState = "found"
+			}
+			var b strings.Builder
+			fmt.Fprintf(&b, "path: %s\n", cfg.Path)
+			fmt.Fprintf(&b, "file: %s\n", fileState)
+			fmt.Fprintf(&b, "%s: %s\n", brokerconfig.KeyProfileFilter, valueOrUnset(cfg.ProfileFilter))
+			fmt.Fprintf(&b, "%s: %s\n", brokerconfig.KeyRegion, valueOrUnset(cfg.Region))
+			fmt.Fprintf(&b, "%s: %s\n", brokerconfig.KeyLogLevel, valueOrUnset(cfg.LogLevel))
+			_, err = io.WriteString(commandWriter(cmd), b.String())
+			return err
+		},
+	}
+}
+
+func configSetCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "set",
+		Usage:     "Set a configuration value (creates the file if absent)",
+		ArgsUsage: "<key> <value>",
+		Description: "Valid keys: " + strings.Join(brokerconfig.Keys, ", ") +
+			". An empty value clears the key.",
+		Action: func(ctx context.Context, cmd *cli.Command) error {
+			args := cmd.Args()
+			if args.Len() != 2 {
+				return fmt.Errorf("config set: expected <key> <value>, got %d argument(s)", args.Len())
+			}
+			key, value := args.Get(0), args.Get(1)
+
+			cfg, err := brokerconfig.Set(ctx, key, value)
+			if err != nil {
+				return fmt.Errorf("config set: %w", err)
+			}
+
+			msg := fmt.Sprintf("set %s = %s in %s\n", key, value, cfg.Path)
+			if value == "" {
+				msg = fmt.Sprintf("cleared %s in %s\n", key, cfg.Path)
+			}
+			_, err = io.WriteString(commandWriter(cmd), msg)
+			return err
+		},
+	}
+}
+
+// valueOrUnset renders an absent configuration value distinctly from an empty
+// string set on disk.
+func valueOrUnset(v string) string {
+	if v == "" {
+		return "(unset; built-in default applies)"
+	}
+	return v
+}

cmd/imds-broker/doctor.go

@@ -24,10 +24,7 @@ func doctorCommand() *cli.Command {
 			profileFilterFlag(),
 		},
 		Action: func(ctx context.Context, cmd *cli.Command) error {
-			w := cmd.Root().Writer
-			if w == nil {
-				w = os.Stdout
-			}
+			w := commandWriter(cmd)
 
 			cfg, err := brokerconfig.Load(ctx)
 			if err != nil {

cmd/imds-broker/main.go

@@ -40,6 +40,7 @@ func main() {
 			serveCommand(),
 			profilesCommand(),
 			mcpCommand(),
+			configCommand(),
 			doctorCommand(),
 			versionCommand(),
 		},

cmd/imds-broker/main_test.go

@@ -164,6 +164,61 @@ func TestEffectiveRegion_ConfigDefaultAndFlagOverride(t *testing.T) {
 		func(c *cli.Command) { assert.Equal(t, "us-east-1", effectiveRegion(c, cfg)) })
 }
 
+// runConfigCmd runs the top-level config command with args, capturing stdout.
+func runConfigCmd(t *testing.T, args ...string) (string, error) {
+	t.Helper()
+	var buf bytes.Buffer
+	cmd := &cli.Command{
+		Name:     "imds-broker",
+		Writer:   &buf,
+		Commands: []*cli.Command{configCommand()},
+	}
+	err := cmd.Run(context.Background(), append([]string{"imds-broker"}, args...))
+	return buf.String(), err
+}
+
+func TestConfigPath_PrintsResolvedLocation(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", dir)
+
+	out, err := runConfigCmd(t, "config", "path")
+	require.NoError(t, err)
+	assert.Contains(t, out, filepath.Join(dir, brokerconfig.RelPath))
+}
+
+func TestConfigList_ReportsUnsetWhenAbsent(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", dir)
+
+	out, err := runConfigCmd(t, "config", "list")
+	require.NoError(t, err)
+	assert.Contains(t, out, "file: not found")
+	assert.Contains(t, out, "profile-filter: (unset")
+}
+
+func TestConfigSet_WritesThenListShows(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", dir)
+
+	out, err := runConfigCmd(t, "config", "set", "region", "ap-southeast-2")
+	require.NoError(t, err)
+	assert.Contains(t, out, "set region = ap-southeast-2")
+
+	out, err = runConfigCmd(t, "config", "list")
+	require.NoError(t, err)
+	assert.Contains(t, out, "file: found")
+	assert.Contains(t, out, "region: ap-southeast-2")
+}
+
+func TestConfigSet_RejectsWrongArgCount(t *testing.T) {
+	dir := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", dir)
+
+	_, err := runConfigCmd(t, "config", "set", "region")
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "expected <key> <value>")
+}
+
 func TestEffectiveLogLevel_Precedence(t *testing.T) {
 	withConfig := &brokerconfig.Config{LogLevel: "debug"}
 	noConfig := &brokerconfig.Config{}