cmd: add CLI

the only command added is 'watch', which serves the only currently
expected functionality of the binary for this lib.

cmd/root.go

@@ -0,0 +1,56 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+package cmd
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/spf13/cobra"
+
+	"git.st8l.com/luxolus/kdnotify/buildinfo"
+)
+
+const (
+	rootHelp     = "A program for responding to Keepalived's VRRP notify events"
+	rootHelpLong = rootHelp + `
+
+This is meant to be used with the 'vrrp_notify <PIPE>' option, see
+man:keepalived.conf(5) for more.`
+)
+
+func Execute() error {
+	return rootCmd().Execute()
+}
+
+func rootCmd() *cobra.Command {
+	root := &cobra.Command{
+		Use:     "kdnotify <subcommand ...>",
+		Short:   rootHelp,
+		Long:    rootHelpLong,
+		Version: fullVersion(),
+	}
+
+	root.AddCommand(watchCmd())
+
+	root.PersistentFlags().String("log-level", "INFO", "Set program log level. ERROR|WARN|INFO|DEBUG")
+
+	return root
+}
+
+func fullVersion() string {
+	v := build.Version
+	hash := build.ShortHash()
+	features := build.FeaturesList()
+
+	vstr := fmt.Sprintf("%s sha=%s", v, hash)
+	if len(features) > 0 {
+		vstr = vstr + "features=" + strings.Join(features, ",")
+	}
+
+	return vstr
+}

cmd/watch.go

@@ -0,0 +1,126 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+package cmd
+
+import (
+	"os"
+
+	"github.com/spf13/cobra"
+	"go.uber.org/zap"
+
+	"git.st8l.com/luxolus/kdnotify/config"
+	"git.st8l.com/luxolus/kdnotify/handler"
+	"git.st8l.com/luxolus/kdnotify/watcher"
+)
+
+const (
+	watchHelp     = "Start a watch on the given PIPE, using the provided CONFIG"
+	watchHelpLong = watchHelp + `
+
+This command creates an IPC FIFO channel at the provided PIPE path.
+
+It is expected that you hand this named PIPE into Keepalived's
+vrrp_notify conf option, and arrange for this program to run before
+Keepalived.
+
+The configuration file can be used to match events Keepalived produces.
+There are four fields: TYPE, STATE, INSTANCE and PRIORITY, with the last
+being optional. You may provide any combination of the above and an action
+to run when a match occurs.
+
+A sample configuration:
+
+---
+watch:
+  context: # Arbitrary structure you can reference via the 'Cxt' key
+    instance1:
+      ip: 192.168.0.1
+      dev: eth0
+  rules: # List of rules to match on
+    - state: [BACKUP, STOP] # Possible actions: MASTER, BACKUP, STOP
+      instance: instance1 # Refers to the name of a vrrp_instance or vrrp_group in Keepalived
+      exec: /bin/ip addr delete {{.Cxt.instance1.ip}} dev {{.Cxt.instance1.dev}}
+    - state: [MASTER]
+      exec: /bin/logger {{.Event.Instance}} is now MASTER with priority: {{.Event.Priority}}
+    - type: [INSTANCE] # Possible types: INSTANCE, GROUP
+      state: [STOP]
+      exec: /bin/logger {{- vip := index .Cxt .Event.Instance -}}{{vip.ip}}%{{vip.dev}} shutdown`
+)
+
+type watchCommand struct {
+	log      *zap.SugaredLogger
+	pipe     string
+	conffile string
+	config   *config.WatchConfig
+	cxt      *config.LibCxt
+}
+
+func (c *watchCommand) PreRunE(cmd *cobra.Command, args []string) error {
+	ll, _ := cmd.Flags().GetString("log-level")
+	cfg, _ := cmd.Flags().GetString("config")
+
+	cxt := config.NewLibCxt(ll)
+	log := cxt.Logger.Named("cli.watch").Sugar()
+
+	log.Debugw("reading config file", "config", cfg)
+	conf, err := os.ReadFile(cfg)
+	if err != nil {
+		return err
+	}
+
+	log.Debug("loading watcher rules and context")
+	config, err := config.WatchConfigFromYAML(conf)
+	if err != nil {
+		return err
+	}
+
+	c.cxt = cxt
+	c.log = log
+	c.conffile = cfg
+	c.config = &config
+	c.pipe = args[0]
+
+	log.Debugw("config loaded",
+		"fifo", c.pipe,
+		"config", c.conffile,
+		"rules", len(c.config.Rules),
+	)
+	return nil
+}
+
+func (c *watchCommand) RunE(cmd *cobra.Command, _ []string) error {
+	h := handler.NewVrrp(c.cxt, c.config)
+	w, err := watcher.NewWatcherFifo(c.cxt, c.pipe)
+	if err != nil {
+		c.log.Errorf("unable to initialize watcher", "error", err)
+		return err
+	}
+
+	c.log.Infow("starting watch",
+		"fifo", c.pipe,
+		"config", c.conffile,
+		"rules", len(c.config.Rules),
+	)
+	return w.Watch(h)
+}
+
+func watchCmd() *cobra.Command {
+	cmd := &watchCommand{}
+
+	watch := &cobra.Command{
+		Use:     "watch [-f CONFIG] <PIPE>",
+		Short:   watchHelp,
+		Long:    watchHelpLong,
+		Args:    cobra.ExactArgs(1),
+		PreRunE: cmd.PreRunE,
+		RunE:    cmd.RunE,
+	}
+
+	watch.Flags().StringP("config", "f", "/etc/kdnotify/config.yaml", "Configuration file, see --help for more")
+
+	return watch
+}