Add event hooking to modules

modules/events.go

@@ -0,0 +1,101 @@
+package modules
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/safing/portbase/log"
+)
+
+type eventHookFn func(context.Context, interface{}) error
+
+type eventHook struct {
+	description   string
+	hookingModule *Module
+	hookFn        eventHookFn
+}
+
+// TriggerEvent executes all hook functions registered to the specified event.
+func (m *Module) TriggerEvent(event string, data interface{}) {
+	go m.processEventTrigger(event, data)
+}
+
+func (m *Module) processEventTrigger(event string, data interface{}) {
+	m.eventHooksLock.RLock()
+	defer m.eventHooksLock.RUnlock()
+
+	hooks, ok := m.eventHooks[event]
+	if !ok {
+		log.Warningf("%s: tried to trigger non-existent event %s", m.Name, event)
+		return
+	}
+
+	for _, hook := range hooks {
+		go m.runEventHook(hook, event, data)
+	}
+}
+
+func (m *Module) runEventHook(hook *eventHook, event string, data interface{}) {
+	if !hook.hookingModule.Started.IsSet() {
+		// target module has not yet fully started, wait until start is complete
+		select {
+		case <-startCompleteSignal:
+		case <-shutdownSignal:
+			return
+		}
+	}
+
+	err := hook.hookingModule.RunWorker(
+		fmt.Sprintf("event hook %s/%s -> %s/%s", m.Name, event, hook.hookingModule.Name, hook.description),
+		func(ctx context.Context) error {
+			return hook.hookFn(ctx, data)
+		},
+	)
+	if err != nil {
+		log.Warningf("%s: failed to execute event hook %s/%s -> %s/%s: %s", hook.hookingModule.Name, m.Name, event, hook.hookingModule.Name, hook.description, err)
+	}
+}
+
+// RegisterEvent registers a new event to allow for registering hooks.
+func (m *Module) RegisterEvent(event string) {
+	m.eventHooksLock.Lock()
+	defer m.eventHooksLock.Unlock()
+
+	_, ok := m.eventHooks[event]
+	if !ok {
+		m.eventHooks[event] = make([]*eventHook, 0, 1)
+	}
+}
+
+// RegisterEventHook registers a hook function with (another) modules' event. Whenever a hook is triggered and the receiving module has not yet fully started, hook execution will be delayed until all modules completed starting.
+func (m *Module) RegisterEventHook(module string, event string, description string, fn func(context.Context, interface{}) error) error {
+	// get target module
+	var eventModule *Module
+	if module == m.Name {
+		eventModule = m
+	} else {
+		var ok bool
+		modulesLock.RLock()
+		eventModule, ok = modules[module]
+		modulesLock.RUnlock()
+		if !ok {
+			return fmt.Errorf("module %s does not exist", module)
+		}
+	}
+
+	// get target event
+	eventModule.eventHooksLock.Lock()
+	defer eventModule.eventHooksLock.Unlock()
+	hooks, ok := eventModule.eventHooks[event]
+	if !ok {
+		return fmt.Errorf("module %s event %s does not exist", eventModule.Name, event)
+	}
+
+	// add hook
+	eventModule.eventHooks[event] = append(hooks, &eventHook{
+		description:   description,
+		hookingModule: m,
+		hookFn:        fn,
+	})
+	return nil
+}