amtool check-config

This is similar to `promtool check-config` and allows one
to validate the alertmanager configuration (as a git presubmit for example).

`govendor fetch github.com/spf13/{cobra,pflag}` was needed to
have support for `Args`.

cli/check_config.go

@@ -0,0 +1,65 @@
+package cli
+
+import (
+	"fmt"
+
+	"github.com/prometheus/alertmanager/config"
+	"github.com/prometheus/alertmanager/template"
+	"github.com/spf13/cobra"
+)
+
+// alertCmd represents the alert command
+var checkConfigCmd = &cobra.Command{
+	Use:   "check-config",
+	Args:  cobra.MinimumNArgs(1),
+	Short: "Validate configuration files for correctness",
+	Long: `Validate configuration files for correctness
+
+Will validate the syntax and schema for alertmanager config file
+and associated templates. Non existing templates will not trigger
+errors`,
+	RunE: checkConfig,
+}
+
+func init() {
+	RootCmd.AddCommand(checkConfigCmd)
+	checkConfigCmd.Flags()
+}
+
+func checkConfig(cmd *cobra.Command, args []string) error {
+	cmd.SilenceUsage = true
+	return CheckConfig(args)
+}
+
+func CheckConfig(args []string) error {
+	failed := 0
+
+	for _, arg := range args {
+		fmt.Printf("Checking '%s'", arg)
+		config, _, err := config.LoadFile(arg)
+		if err != nil {
+			fmt.Printf("  FAILED: %s\n", err)
+			failed += 1
+		} else {
+			fmt.Printf("  SUCCESS\n")
+		}
+
+		if config != nil {
+			fmt.Printf("Found %d templates: ", len(config.Templates))
+			if len(config.Templates) > 0 {
+				_, err = template.FromGlobs(config.Templates...)
+				if err != nil {
+					fmt.Printf("  FAILED: %s\n", err)
+					failed += 1
+				} else {
+					fmt.Printf("  SUCCESS\n")
+				}
+			}
+		}
+		fmt.Printf("\n")
+	}
+	if failed > 0 {
+		return fmt.Errorf("Failed to validate %d file(s).", failed)
+	}
+	return nil
+}

cli/check_config_test.go

@@ -0,0 +1,17 @@
+package cli
+
+import (
+	"testing"
+)
+
+func TestCheckConfig(t *testing.T) {
+	err := CheckConfig([]string{"testdata/conf.good.yml"})
+	if err != nil {
+		t.Fatalf("Checking valid config file failed with: %v", err)
+	}
+
+	err = CheckConfig([]string{"testdata/conf.bad.yml"})
+	if err == nil {
+		t.Fatalf("Failed to detect invalid file.")
+	}
+}

cli/testdata/conf.bad.yml

@@ -0,0 +1 @@
+BAD

cli/testdata/conf.good.yml

@@ -0,0 +1,11 @@
+global:
+  smtp_smarthost: 'localhost:25'
+
+templates:
+  - '/etc/alertmanager/template/*.tmpl'
+
+route:
+  receiver: default
+
+receivers:
+  - name: default