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caddy/modules/caddyevents/app.go
2024-06-06 07:11:28 -06:00

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12 KiB
Go

// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package caddyevents
import (
"context"
"encoding/json"
"errors"
"fmt"
"strings"
"time"
"github.com/google/uuid"
"go.uber.org/zap"
"github.com/caddyserver/caddy/v2"
)
func init() {
caddy.RegisterModule(App{})
}
// App implements a global eventing system within Caddy.
// Modules can emit and subscribe to events, providing
// hooks into deep parts of the code base that aren't
// otherwise accessible. Events provide information about
// what and when things are happening, and this facility
// allows handlers to take action when events occur,
// add information to the event's metadata, and even
// control program flow in some cases.
//
// Events are propagated in a DOM-like fashion. An event
// emitted from module `a.b.c` (the "origin") will first
// invoke handlers listening to `a.b.c`, then `a.b`,
// then `a`, then those listening regardless of origin.
// If a handler returns the special error Aborted, then
// propagation immediately stops and the event is marked
// as aborted. Emitters may optionally choose to adjust
// program flow based on an abort.
//
// Modules can subscribe to events by origin and/or name.
// A handler is invoked only if it is subscribed to the
// event by name and origin. Subscriptions should be
// registered during the provisioning phase, before apps
// are started.
//
// Event handlers are fired synchronously as part of the
// regular flow of the program. This allows event handlers
// to control the flow of the program if the origin permits
// it and also allows handlers to convey new information
// back into the origin module before it continues.
// In essence, event handlers are similar to HTTP
// middleware handlers.
//
// Event bindings/subscribers are unordered; i.e.
// event handlers are invoked in an arbitrary order.
// Event handlers should not rely on the logic of other
// handlers to succeed.
//
// The entirety of this app module is EXPERIMENTAL and
// subject to change. Pay attention to release notes.
type App struct {
// Subscriptions bind handlers to one or more events
// either globally or scoped to specific modules or module
// namespaces.
Subscriptions []*Subscription `json:"subscriptions,omitempty"`
// Map of event name to map of module ID/namespace to handlers
subscriptions map[string]map[caddy.ModuleID][]Handler
logger *zap.Logger
started bool
}
// Subscription represents binding of one or more handlers to
// one or more events.
type Subscription struct {
// The name(s) of the event(s) to bind to. Default: all events.
Events []string `json:"events,omitempty"`
// The ID or namespace of the module(s) from which events
// originate to listen to for events. Default: all modules.
//
// Events propagate up, so events emitted by module "a.b.c"
// will also trigger the event for "a.b" and "a". Thus, to
// receive all events from "a.b.c" and "a.b.d", for example,
// one can subscribe to either "a.b" or all of "a" entirely.
Modules []caddy.ModuleID `json:"modules,omitempty"`
// The event handler modules. These implement the actual
// behavior to invoke when an event occurs. At least one
// handler is required.
HandlersRaw []json.RawMessage `json:"handlers,omitempty" caddy:"namespace=events.handlers inline_key=handler"`
// The decoded handlers; Go code that is subscribing to
// an event should set this field directly; HandlersRaw
// is meant for JSON configuration to fill out this field.
Handlers []Handler `json:"-"`
}
// CaddyModule returns the Caddy module information.
func (App) CaddyModule() caddy.ModuleInfo {
return caddy.ModuleInfo{
ID: "events",
New: func() caddy.Module { return new(App) },
}
}
// Provision sets up the app.
func (app *App) Provision(ctx caddy.Context) error {
app.logger = ctx.Logger()
app.subscriptions = make(map[string]map[caddy.ModuleID][]Handler)
for _, sub := range app.Subscriptions {
if sub.HandlersRaw != nil {
handlersIface, err := ctx.LoadModule(sub, "HandlersRaw")
if err != nil {
return fmt.Errorf("loading event subscriber modules: %v", err)
}
for _, h := range handlersIface.([]any) {
sub.Handlers = append(sub.Handlers, h.(Handler))
}
if len(sub.Handlers) == 0 {
// pointless to bind without any handlers
return fmt.Errorf("no handlers defined")
}
}
}
return nil
}
// Start runs the app.
func (app *App) Start() error {
for _, sub := range app.Subscriptions {
if err := app.Subscribe(sub); err != nil {
return err
}
}
app.started = true
return nil
}
// Stop gracefully shuts down the app.
func (app *App) Stop() error {
return nil
}
// Subscribe binds one or more event handlers to one or more events
// according to the subscription s. For now, subscriptions can only
// be created during the provision phase; new bindings cannot be
// created after the events app has started.
func (app *App) Subscribe(s *Subscription) error {
if app.started {
return fmt.Errorf("events already started; new subscriptions closed")
}
// handle special case of catch-alls (omission of event name or module space implies all)
if len(s.Events) == 0 {
s.Events = []string{""}
}
if len(s.Modules) == 0 {
s.Modules = []caddy.ModuleID{""}
}
for _, eventName := range s.Events {
if app.subscriptions[eventName] == nil {
app.subscriptions[eventName] = make(map[caddy.ModuleID][]Handler)
}
for _, originModule := range s.Modules {
app.subscriptions[eventName][originModule] = append(app.subscriptions[eventName][originModule], s.Handlers...)
}
}
return nil
}
// On is syntactic sugar for Subscribe() that binds a single handler
// to a single event from any module. If the eventName is empty string,
// it counts for all events.
func (app *App) On(eventName string, handler Handler) error {
return app.Subscribe(&Subscription{
Events: []string{eventName},
Handlers: []Handler{handler},
})
}
// Emit creates and dispatches an event named eventName to all relevant handlers with
// the metadata data. Events are emitted and propagated synchronously. The returned Event
// value will have any additional information from the invoked handlers.
//
// Note that the data map is not copied, for efficiency. After Emit() is called, the
// data passed in should not be changed in other goroutines.
func (app *App) Emit(ctx caddy.Context, eventName string, data map[string]any) Event {
logger := app.logger.With(zap.String("name", eventName))
id, err := uuid.NewRandom()
if err != nil {
logger.Error("failed generating new event ID", zap.Error(err))
}
eventName = strings.ToLower(eventName)
e := Event{
Data: data,
id: id,
ts: time.Now(),
name: eventName,
origin: ctx.Module(),
}
logger = logger.With(
zap.String("id", e.id.String()),
zap.String("origin", e.origin.CaddyModule().String()))
// add event info to replacer, make sure it's in the context
repl, ok := ctx.Context.Value(caddy.ReplacerCtxKey).(*caddy.Replacer)
if !ok {
repl = caddy.NewReplacer()
ctx.Context = context.WithValue(ctx.Context, caddy.ReplacerCtxKey, repl)
}
repl.Map(func(key string) (any, bool) {
switch key {
case "event":
return e, true
case "event.id":
return e.id, true
case "event.name":
return e.name, true
case "event.time":
return e.ts, true
case "event.time_unix":
return e.ts.UnixMilli(), true
case "event.module":
return e.origin.CaddyModule().ID, true
case "event.data":
return e.Data, true
}
if strings.HasPrefix(key, "event.data.") {
key = strings.TrimPrefix(key, "event.data.")
if val, ok := e.Data[key]; ok {
return val, true
}
}
return nil, false
})
logger = logger.With(zap.Any("data", e.Data))
logger.Debug("event")
// invoke handlers bound to the event by name and also all events; this for loop
// iterates twice at most: once for the event name, once for "" (all events)
for {
moduleID := e.origin.CaddyModule().ID
// implement propagation up the module tree (i.e. start with "a.b.c" then "a.b" then "a" then "")
for {
if app.subscriptions[eventName] == nil {
break // shortcut if event not bound at all
}
for _, handler := range app.subscriptions[eventName][moduleID] {
select {
case <-ctx.Done():
logger.Error("context canceled; event handling stopped")
return e
default:
}
// this log can be a useful sanity check to ensure your handlers are in fact being invoked
// (see https://github.com/mholt/caddy-events-exec/issues/6)
logger.Debug("invoking subscribed handler",
zap.String("subscribed_to", eventName),
zap.Any("handler", handler))
if err := handler.Handle(ctx, e); err != nil {
aborted := errors.Is(err, ErrAborted)
logger.Error("handler error",
zap.Error(err),
zap.Bool("aborted", aborted))
if aborted {
e.Aborted = err
return e
}
}
}
if moduleID == "" {
break
}
lastDot := strings.LastIndex(string(moduleID), ".")
if lastDot < 0 {
moduleID = "" // include handlers bound to events regardless of module
} else {
moduleID = moduleID[:lastDot]
}
}
// include handlers listening to all events
if eventName == "" {
break
}
eventName = ""
}
return e
}
// 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: As with the rest of this package, 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 map[string]any
id uuid.UUID
ts time.Time
name string
origin caddy.Module
}
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() caddy.Module { return e.origin }
// 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.
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"`
}
// ErrAborted cancels an event.
var ErrAborted = errors.New("event aborted")
// Handler is a type that can handle events.
type Handler interface {
Handle(context.Context, Event) error
}
// Interface guards
var (
_ caddy.App = (*App)(nil)
_ caddy.Provisioner = (*App)(nil)
)