events: Refactor; move Event into core, so core can emit events (#6930)

* events: Refactor; move Event into core, so core can emit events

Requires some slight trickery to invert dependencies. We can't have the caddy package import the caddyevents package, because caddyevents imports caddy. Interface to the rescue!

Also add two new events, experimentally: started, and stopping. At the request of a sponsor.

Also rename "Filesystems" to "FileSystems" to match Go convention (unrelated to events, was just bugging me when I noticed it).

* Coupla bug fixes

* lol whoops

Author: mholt

caddy.go

@@ -81,13 +81,14 @@ type Config struct {
 	// associated value.
 	AppsRaw ModuleMap `json:"apps,omitempty" caddy:"namespace="`
 
-	apps    map[string]App
-	storage certmagic.Storage
+	apps         map[string]App
+	storage      certmagic.Storage
+	eventEmitter eventEmitter
 
 	cancelFunc context.CancelFunc
 
-	// filesystems is a dict of filesystems that will later be loaded from and added to.
-	filesystems FileSystems
+	// fileSystems is a dict of fileSystems that will later be loaded from and added to.
+	fileSystems FileSystems
 }
 
 // App is a thing that Caddy runs.
@@ -442,6 +443,10 @@ func run(newCfg *Config, start bool) (Context, error) {
 	}
 	globalMetrics.configSuccess.Set(1)
 	globalMetrics.configSuccessTime.SetToCurrentTime()
+
+	// TODO: This event is experimental and subject to change.
+	ctx.emitEvent("started", nil)
+
 	// now that the user's config is running, finish setting up anything else,
 	// such as remote admin endpoint, config loader, etc.
 	return ctx, finishSettingUp(ctx, ctx.cfg)
@@ -509,7 +514,7 @@ func provisionContext(newCfg *Config, replaceAdminServer bool) (Context, error)
 	}
 
 	// create the new filesystem map
-	newCfg.filesystems = &filesystems.FilesystemMap{}
+	newCfg.fileSystems = &filesystems.FileSystemMap{}
 
 	// prepare the new config for use
 	newCfg.apps = make(map[string]App)
@@ -696,6 +701,9 @@ func unsyncedStop(ctx Context) {
 		return
 	}
 
+	// TODO: This event is experimental and subject to change.
+	ctx.emitEvent("stopping", nil)
+
 	// stop each app
 	for name, a := range ctx.cfg.apps {
 		err := a.Stop()
@@ -1038,6 +1046,92 @@ func Version() (simple, full string) {
 	return
 }
 
+// Event represents something that has happened or is happening.
+// An Event value is not synchronized, so it should be copied if
+// being used in goroutines.
+//
+// EXPERIMENTAL: Events are subject to change.
+type Event struct {
+	// If non-nil, the event has been aborted, meaning
+	// propagation has stopped to other handlers and
+	// the code should stop what it was doing. Emitters
+	// may choose to use this as a signal to adjust their
+	// code path appropriately.
+	Aborted error
+
+	// The data associated with the event. Usually the
+	// original emitter will be the only one to set or
+	// change these values, but the field is exported
+	// so handlers can have full access if needed.
+	// However, this map is not synchronized, so
+	// handlers must not use this map directly in new
+	// goroutines; instead, copy the map to use it in a
+	// goroutine. Data may be nil.
+	Data map[string]any
+
+	id     uuid.UUID
+	ts     time.Time
+	name   string
+	origin Module
+}
+
+// NewEvent creates a new event, but does not emit the event. To emit an
+// event, call Emit() on the current instance of the caddyevents app insteaad.
+//
+// EXPERIMENTAL: Subject to change.
+func NewEvent(ctx Context, name string, data map[string]any) (Event, error) {
+	id, err := uuid.NewRandom()
+	if err != nil {
+		return Event{}, fmt.Errorf("generating new event ID: %v", err)
+	}
+	name = strings.ToLower(name)
+	return Event{
+		Data:   data,
+		id:     id,
+		ts:     time.Now(),
+		name:   name,
+		origin: ctx.Module(),
+	}, nil
+}
+
+func (e Event) ID() uuid.UUID        { return e.id }
+func (e Event) Timestamp() time.Time { return e.ts }
+func (e Event) Name() string         { return e.name }
+func (e Event) Origin() Module       { return e.origin } // Returns the module that originated the event. May be nil, usually if caddy core emits the event.
+
+// CloudEvent exports event e as a structure that, when
+// serialized as JSON, is compatible with the
+// CloudEvents spec.
+func (e Event) CloudEvent() CloudEvent {
+	dataJSON, _ := json.Marshal(e.Data)
+	return CloudEvent{
+		ID:              e.id.String(),
+		Source:          e.origin.CaddyModule().String(),
+		SpecVersion:     "1.0",
+		Type:            e.name,
+		Time:            e.ts,
+		DataContentType: "application/json",
+		Data:            dataJSON,
+	}
+}
+
+// CloudEvent is a JSON-serializable structure that
+// is compatible with the CloudEvents specification.
+// See https://cloudevents.io.
+// EXPERIMENTAL: Subject to change.
+type CloudEvent struct {
+	ID              string          `json:"id"`
+	Source          string          `json:"source"`
+	SpecVersion     string          `json:"specversion"`
+	Type            string          `json:"type"`
+	Time            time.Time       `json:"time"`
+	DataContentType string          `json:"datacontenttype,omitempty"`
+	Data            json.RawMessage `json:"data,omitempty"`
+}
+
+// ErrEventAborted cancels an event.
+var ErrEventAborted = errors.New("event aborted")
+
 // ActiveContext returns the currently-active context.
 // This function is experimental and might be changed
 // or removed in the future.

context.go

@@ -91,14 +91,14 @@ func (ctx *Context) OnCancel(f func()) {
 	ctx.cleanupFuncs = append(ctx.cleanupFuncs, f)
 }
 
-// Filesystems returns a ref to the FilesystemMap.
+// FileSystems returns a ref to the FilesystemMap.
 // EXPERIMENTAL: This API is subject to change.
-func (ctx *Context) Filesystems() FileSystems {
+func (ctx *Context) FileSystems() FileSystems {
 	// if no config is loaded, we use a default filesystemmap, which includes the osfs
 	if ctx.cfg == nil {
-		return &filesystems.FilesystemMap{}
+		return &filesystems.FileSystemMap{}
 	}
-	return ctx.cfg.filesystems
+	return ctx.cfg.fileSystems
 }
 
 // Returns the active metrics registry for the context
@@ -277,6 +277,14 @@ func (ctx Context) LoadModule(structPointer any, fieldName string) (any, error)
 	return result, nil
 }
 
+// emitEvent is a small convenience method so the caddy core can emit events, if the event app is configured.
+func (ctx Context) emitEvent(name string, data map[string]any) Event {
+	if ctx.cfg == nil || ctx.cfg.eventEmitter == nil {
+		return Event{}
+	}
+	return ctx.cfg.eventEmitter.Emit(ctx, name, data)
+}
+
 // loadModulesFromSomeMap loads modules from val, which must be a type of map[string]any.
 // Depending on inlineModuleKey, it will be interpreted as either a ModuleMap (key is the module
 // name) or as a regular map (key is not the module name, and module name is defined inline).
@@ -429,6 +437,14 @@ func (ctx Context) LoadModuleByID(id string, rawMsg json.RawMessage) (any, error
 
 	ctx.moduleInstances[id] = append(ctx.moduleInstances[id], val)
 
+	// if the loaded module happens to be an app that can emit events, store it so the
+	// core can have access to emit events without an import cycle
+	if ee, ok := val.(eventEmitter); ok {
+		if _, ok := ee.(App); ok {
+			ctx.cfg.eventEmitter = ee
+		}
+	}
+
 	return val, nil
 }
 
@@ -600,3 +616,11 @@ func (ctx *Context) WithValue(key, value any) Context {
 		exitFuncs:       ctx.exitFuncs,
 	}
 }
+
+// eventEmitter is a small interface that inverts dependencies for
+// the caddyevents package, so the core can emit events without an
+// import cycle (i.e. the caddy package doesn't have to import
+// the caddyevents package, which imports the caddy package).
+type eventEmitter interface {
+	Emit(ctx Context, eventName string, data map[string]any) Event
+}

internal/filesystems/map.go

@@ -7,35 +7,35 @@ import (
 )
 
 const (
-	DefaultFilesystemKey = "default"
+	DefaultFileSystemKey = "default"
 )
 
-var DefaultFilesystem = &wrapperFs{key: DefaultFilesystemKey, FS: OsFS{}}
+var DefaultFileSystem = &wrapperFs{key: DefaultFileSystemKey, FS: OsFS{}}
 
 // wrapperFs exists so can easily add to wrapperFs down the line
 type wrapperFs struct {
 	key string
 	fs.FS
 }
 
-// FilesystemMap stores a map of filesystems
+// FileSystemMap stores a map of filesystems
 // the empty key will be overwritten to be the default key
 // it includes a default filesystem, based off the os fs
-type FilesystemMap struct {
+type FileSystemMap struct {
 	m sync.Map
 }
 
 // note that the first invocation of key cannot be called in a racy context.
-func (f *FilesystemMap) key(k string) string {
+func (f *FileSystemMap) key(k string) string {
 	if k == "" {
-		k = DefaultFilesystemKey
+		k = DefaultFileSystemKey
 	}
 	return k
 }
 
 // Register will add the filesystem with key to later be retrieved
 // A call with a nil fs will call unregister, ensuring that a call to Default() will never be nil
-func (f *FilesystemMap) Register(k string, v fs.FS) {
+func (f *FileSystemMap) Register(k string, v fs.FS) {
 	k = f.key(k)
 	if v == nil {
 		f.Unregister(k)
@@ -47,31 +47,31 @@ func (f *FilesystemMap) Register(k string, v fs.FS) {
 // Unregister will remove the filesystem with key from the filesystem map
 // if the key is the default key, it will set the default to the osFS instead of deleting it
 // modules should call this on cleanup to be safe
-func (f *FilesystemMap) Unregister(k string) {
+func (f *FileSystemMap) Unregister(k string) {
 	k = f.key(k)
-	if k == DefaultFilesystemKey {
-		f.m.Store(k, DefaultFilesystem)
+	if k == DefaultFileSystemKey {
+		f.m.Store(k, DefaultFileSystem)
 	} else {
 		f.m.Delete(k)
 	}
 }
 
 // Get will get a filesystem with a given key
-func (f *FilesystemMap) Get(k string) (v fs.FS, ok bool) {
+func (f *FileSystemMap) Get(k string) (v fs.FS, ok bool) {
 	k = f.key(k)
 	c, ok := f.m.Load(strings.TrimSpace(k))
 	if !ok {
-		if k == DefaultFilesystemKey {
-			f.m.Store(k, DefaultFilesystem)
-			return DefaultFilesystem, true
+		if k == DefaultFileSystemKey {
+			f.m.Store(k, DefaultFileSystem)
+			return DefaultFileSystem, true
 		}
 		return nil, ok
 	}
 	return c.(fs.FS), true
 }
 
 // Default will get the default filesystem in the filesystem map
-func (f *FilesystemMap) Default() fs.FS {
-	val, _ := f.Get(DefaultFilesystemKey)
+func (f *FileSystemMap) Default() fs.FS {
+	val, _ := f.Get(DefaultFileSystemKey)
 	return val
 }