Introducing Event Hooks Plugins (#1537)

* add Hook

* update hooks

* remove parenthesis

* Update requests

caddy/caddymain/run.go

@@ -100,11 +100,8 @@ func Run() {
 		mustLogFatalf("%v", err)
 	}
 
-	// Execute plugins that are registered to run as the process starts
-	err = caddy.StartupHooks(serverType)
-	if err != nil {
-		mustLogFatalf("%v", err)
-	}
+	// Executes Startup events
+	caddy.EmitEvent(caddy.StartupEvent)
 
 	// Get Caddyfile input
 	caddyfileinput, err := caddy.LoadCaddyfile(serverType)

plugins.go

@@ -2,6 +2,7 @@ package caddy
 
 import (
 	"fmt"
+	"log"
 	"net"
 	"sort"
 
@@ -21,6 +22,10 @@ var (
 	// must have a name.
 	plugins = make(map[string]map[string]Plugin)
 
+	// eventHooks is a map of hook name to Hook. All hooks plugins
+	// must have a name.
+	eventHooks = make(map[string]EventHook)
+
 	// parsingCallbacks maps server type to map of directive
 	// to list of callback functions. These aren't really
 	// plugins on their own, but are often registered from
@@ -69,30 +74,6 @@ func DescribePlugins() string {
 	return str
 }
 
-// StartupHooks executes the startup hooks defined when the
-// plugins were registered and returns the first error
-// it encounters.
-func StartupHooks(serverType string) error {
-	for stype, stypePlugins := range plugins {
-		if stype != "" && stype != serverType {
-			continue
-		}
-
-		for name := range stypePlugins {
-			if stypePlugins[name].StartupHook == nil {
-				continue
-			}
-
-			err := stypePlugins[name].StartupHook()
-			if err != nil {
-				return err
-			}
-		}
-	}
-
-	return nil
-}
-
 // ValidDirectives returns the list of all directives that are
 // recognized for the server type serverType. However, not all
 // directives may be installed. This makes it possible to give
@@ -200,10 +181,6 @@ type Plugin struct {
 	// Action is the plugin's setup function, if associated
 	// with a directive in the Caddyfile.
 	Action SetupFunc
-
-	// StartupHook is the plugin's function that is executed
-	// immediately after the flag parsing.
-	StartupHook func() error
 }
 
 // RegisterPlugin plugs in plugin. All plugins should register
@@ -228,6 +205,42 @@ func RegisterPlugin(name string, plugin Plugin) {
 	plugins[plugin.ServerType][name] = plugin
 }
 
+// EventName represents the name of an event used with event hooks.
+type EventName string
+
+const (
+	StartupEvent  EventName = "startup"
+	ShutdownEvent EventName = "shutdown"
+)
+
+// EventHook is a type which holds information about a startup hook plugin.
+type EventHook func(eventType EventName) error
+
+// RegisterEventHook plugs in hook. All the hooks should register themselves
+// and they must have a name.
+func RegisterEventHook(name string, hook EventHook) {
+	if name == "" {
+		panic("event hook must have a name")
+	}
+	if _, dup := eventHooks[name]; dup {
+		panic("hook named " + name + " already registered")
+	}
+	eventHooks[name] = hook
+}
+
+// EmitEvent executes the different hooks passing the EventType as an
+// argument. This is a blocking function. Hook developers should
+// use 'go' keyword if they don't want to block Caddy.
+func EmitEvent(event EventName) {
+	for name, hook := range eventHooks {
+		err := hook(event)
+
+		if err != nil {
+			log.Printf("error on '%s' hook: %v", name, err)
+		}
+	}
+}
+
 // ParsingCallback is a function that is called after
 // a directive's setup functions have been executed
 // for all the server blocks.

sigtrap.go

@@ -52,6 +52,9 @@ func trapSignalsCrossPlatform() {
 // This function is idempotent; subsequent invocations always return 0.
 func executeShutdownCallbacks(signame string) (exitCode int) {
 	shutdownCallbacksOnce.Do(func() {
+		// execute third-party shutdown hooks
+		EmitEvent(ShutdownEvent)
+
 		errs := allShutdownCallbacks()
 		if len(errs) > 0 {
 			for _, err := range errs {