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event_handler.go
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/
event_handler.go
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package state
import (
"errors"
"reflect"
"sync"
"github.com/diamondburned/arikawa/v2/gateway"
)
var (
// ErrInvalidHandler gets returned if a handler given to
// EventManager.AddHandler or EventManager.MustAddHandler is not a valid
// handler func, i.e. not following the form of func(*State, e) where e is
// either a pointer to an event, *Base or interface{}.
ErrInvalidHandler = errors.New("state: the passed interface{} does not resemble a valid handler")
// ErrInvalidMiddleware gets returned if a middleware given to
// EventManger.AddHandler or EventManager.MustAddHandler has not the same
// type as its handler.
//
// Additionally, it is returned by AddMiddleware and
// MustAddMiddleware if the middleware func is invalid.
ErrInvalidMiddleware = errors.New("state: the passed middleware does not match the type of the handler")
// Filtered should be returned if a filter blocks an event.
Filtered = errors.New("filtered") //nolint:golint,stylecheck
)
type (
EventHandler struct {
s *State
sv reflect.Value
handlers map[reflect.Type][]*genericHandler
handlersMutex sync.RWMutex
globalMiddlewares map[reflect.Type][]globalMiddleware
globalMiddlewaresMutex sync.RWMutex
wg sync.WaitGroup
ErrorHandler func(err error)
PanicHandler func(err interface{})
// currentSerial is the next available serial number.
// This is used to preserve the order of global middlewares.
currentSerial uint64
closer chan<- struct{}
}
globalMiddleware struct {
middleware reflect.Value
serial uint64
}
// genericHandler wraps an event handler alongside it's middlewares.
genericHandler struct {
handler reflect.Value
channel bool
once *sync.Once
rm func()
// middlewares are the middlewares for the handler.
middlewares []middleware
}
middleware struct {
middleware reflect.Value
typ reflect.Type
}
)
// NewEventHandler creates a new EventHandler.
func NewEventHandler(s *State) *EventHandler {
// make sure state update is blocking
s.State.Session.Handler.Synchronous = true
return &EventHandler{
s: s,
sv: reflect.ValueOf(s),
handlers: make(map[reflect.Type][]*genericHandler),
globalMiddlewares: make(map[reflect.Type][]globalMiddleware),
ErrorHandler: func(error) {},
PanicHandler: func(interface{}) {},
}
}
// Open starts listening for events until the returned closer function is
// called.
func (h *EventHandler) Open(events <-chan interface{}) {
closer := make(chan struct{})
h.closer = closer
go func() {
for {
select {
case <-closer:
return
case gatewayEvent := <-events:
e := h.genEvent(gatewayEvent)
if e == nil {
break
}
// prevent premature closer between here and when the first handler is called
h.wg.Add(1)
h.s.Session.Call(gatewayEvent) // trigger state update
go func() {
h.Call(e)
h.wg.Done()
}()
}
}
}()
}
// Close stops the event listener and blocks until all handlers have finished
// executing.
func (h *EventHandler) Close() {
if h.closer != nil {
close(h.closer)
h.closer = nil
h.wg.Wait()
}
}
// DeriveIntents derives the intents based on the event handlers and global
// middlewares that were added.
// Interface and Base handlers will not be taken into account.
//
// Note that this does not reflect the intents needed to enable caching for
// API calls made anywhere in code.
func (h *EventHandler) DeriveIntents() (i gateway.Intents) {
h.globalMiddlewaresMutex.RLock()
for t := range h.globalMiddlewares {
i |= eventIntents[t]
}
h.globalMiddlewaresMutex.RUnlock()
h.handlersMutex.RLock()
for t := range h.handlers {
i |= eventIntents[t]
}
h.handlersMutex.RUnlock()
return
}
var (
interfaceType = reflect.TypeOf((*interface{})(nil)).Elem()
baseType = reflect.TypeOf(new(Base))
stateType = reflect.TypeOf(new(State))
errorType = reflect.TypeOf((*error)(nil)).Elem()
)
// AddHandler adds a handler with the passed middlewares to the event handlers.
// A handler can either be a function, or a channel of type chan *eventType.
// Note, however, that channel sends are non-blocking, and you must either
// buffer your channel sufficiently, or ensure you are listening.
//
// The signature of a handler func is func(*State, e) where e is either a
// pointer to an event, *Base or interface{}.
// Optionally, a handler may return an error.
//
// Middlewares must be of the same type as the handlers or must be an
// interface{} or Base handlers.
func (h *EventHandler) AddHandler(handler interface{}, middlewares ...interface{}) (rm func(), err error) {
return h.addHandler(handler, false, middlewares...)
}
// MustAddHandler is the same as AddHandler, but panics if AddHandler returns
// an error.
func (h *EventHandler) MustAddHandler(handler interface{}, middlewares ...interface{}) func() {
rm, err := h.AddHandler(handler, middlewares...)
if err != nil {
panic(err)
}
return rm
}
// AddHandlerOnce adds a handler that is only executed once.
// If middlewares prevent execution, the handler will be executed on the next
// event.
func (h *EventHandler) AddHandlerOnce(handler interface{}, middlewares ...interface{}) error {
_, err := h.addHandler(handler, true, middlewares...)
return err
}
// MustAddHandlerOnce is the same as AddHandlerOnce, but panics if
// AddHandlerOnce returns an error.
func (h *EventHandler) MustAddHandlerOnce(handler interface{}, middlewares ...interface{}) {
err := h.AddHandlerOnce(handler, middlewares...)
if err != nil {
panic(err)
}
}
// AutoAddHandlers adds all handlers methods of the passed struct to the
// EventHandler.
// scan must be a pointer to a struct.
func (h *EventHandler) AutoAddHandlers(scan interface{}, middlewares ...interface{}) {
v := reflect.ValueOf(scan)
if v.Kind() != reflect.Ptr {
return
}
for i := 0; i < v.NumMethod(); i++ {
m := v.Method(i)
if m.CanInterface() {
// just try, AddHandler will abort if m is not a valid
// handler func
_, _ = h.AddHandler(m.Interface(), middlewares...)
}
}
}
func (h *EventHandler) addHandler(
handler interface{}, execOnce bool, middlewares ...interface{},
) (rm func(), err error) {
handlerVal := reflect.ValueOf(handler)
handlerType := handlerVal.Type()
var eventType reflect.Type
switch handlerType.Kind() {
case reflect.Chan:
eventType = handlerType.Elem()
case reflect.Func:
// we expect two input params, first must be state
if handlerType.NumIn() != 2 || handlerType.In(0) != stateType {
return nil, ErrInvalidHandler
// we expect either no return or an error return
} else if handlerType.NumOut() != 0 && (handlerType.NumOut() != 1 || handlerType.Out(0) != errorType) {
return nil, ErrInvalidHandler
}
eventType = handlerType.In(1)
default:
return nil, ErrInvalidHandler
}
gh := &genericHandler{
handler: handlerVal,
channel: handlerType.Kind() == reflect.Chan,
}
gh.middlewares, err = h.extractMiddlewares(middlewares, eventType)
if err != nil {
return nil, err
}
var once sync.Once
rm = func() {
once.Do(func() {
h.handlersMutex.Lock()
defer h.handlersMutex.Unlock()
handler := h.handlers[handlerType]
for i, ha := range handler {
if ha == gh {
h.handlers[handlerType] = append(handler[:i], handler[i+1:]...)
break
}
}
})
}
if execOnce {
gh.once = new(sync.Once)
gh.rm = rm
}
h.handlersMutex.Lock()
h.handlers[eventType] = append(h.handlers[eventType], gh)
h.handlersMutex.Unlock()
return rm, nil
}
func (h *EventHandler) extractMiddlewares(raw []interface{}, eventType reflect.Type) ([]middleware, error) {
mw := make([]middleware, len(raw))
for i, m := range raw {
mv := reflect.ValueOf(m)
mt := mv.Type()
if mt.Kind() != reflect.Func {
return nil, ErrInvalidMiddleware
}
// we expect two input params, first must be state
if mt.NumIn() != 2 || mt.In(0) != stateType {
return nil, ErrInvalidMiddleware
// we expect either no return or an error return
} else if mt.NumOut() != 0 && (mt.NumOut() != 1 || mt.Out(0) != errorType) {
return nil, ErrInvalidMiddleware
}
switch met := mt.In(1); met {
case interfaceType, baseType, eventType:
mw[i] = middleware{
middleware: mv,
typ: met,
}
default:
return nil, ErrInvalidMiddleware
}
}
return mw, nil
}
// AddMiddleware adds the passed middleware as a global middleware.
//
// The signature of a middleware func is func(*State, e) where e is either a
// pointer to an event, *Base or interface{}.
// Optionally, a middleware may return an error.
func (h *EventHandler) AddMiddleware(f interface{}) error {
fv := reflect.ValueOf(f)
ft := fv.Type()
// we expect two input params, first must be state
if ft.NumIn() != 2 || ft.In(0) != stateType {
return ErrInvalidMiddleware
// we expect either no return or an error return
} else if ft.NumOut() != 0 && (ft.NumOut() != 1 || ft.Out(0) != errorType) {
return ErrInvalidMiddleware
}
et := ft.In(1)
h.globalMiddlewaresMutex.Lock()
defer h.globalMiddlewaresMutex.Unlock()
h.globalMiddlewares[et] = append(h.globalMiddlewares[et], globalMiddleware{
middleware: fv,
serial: h.currentSerial,
})
h.currentSerial++
return nil
}
// MustAddMiddleware is the same as AddMiddleware but panics if AddMiddleware
// returns an error.
func (h *EventHandler) MustAddMiddleware(f interface{}) {
err := h.AddMiddleware(f)
if err != nil {
panic(err)
}
}
// Call can be used to manually dispatch an event.
// For this to succeed, e must be a pointer to an event, and it's Base field
// must be set.
func (h *EventHandler) Call(e interface{}) {
ev := reflect.ValueOf(e)
et := reflect.TypeOf(e)
abort := h.callGlobalMiddlewares(ev, et)
ev = ev.Elem() // from now functions only take elem
direct := false
switch e := e.(type) {
case *ReadyEvent:
h.handleReady(e)
case *GuildCreateEvent:
specificEvent := h.handleGuildCreate(e)
if !abort {
sev := reflect.ValueOf(specificEvent)
set := reflect.TypeOf(specificEvent)
h.call(sev, set, false)
}
direct = true
case *GuildDeleteEvent:
specificEvent := h.handleGuildDelete(e)
if !abort {
sev := reflect.ValueOf(specificEvent)
set := reflect.TypeOf(specificEvent)
h.call(sev, set, false)
}
direct = true
}
if !abort {
h.call(ev, et, direct)
}
}
// call calls the handlers for the passed typed using the event wrapped in ev.
// ev must not be a pointer, however, et is expected to be the pointerized type
// of ev.
//
// direct specifies, whether or not interface and Base handlers should be
// called for the event as well.
func (h *EventHandler) call(ev reflect.Value, et reflect.Type, direct bool) {
h.handlersMutex.RLock()
defer h.handlersMutex.RUnlock()
if !direct {
h.callHandlers(ev, et, h.handlers[interfaceType])
h.callHandlers(ev, et, h.handlers[baseType])
}
h.callHandlers(ev, et, h.handlers[et])
}
// callHandlers calls the passed slice of handlers using the passed event ev.
// ev must not be a pointer, however, et is expected to be the pointerized type
// of ev.
func (h *EventHandler) callHandlers(ev reflect.Value, et reflect.Type, handlers []*genericHandler) {
h.wg.Add(len(handlers))
for _, gh := range handlers {
go func(gh *genericHandler) {
defer h.wg.Done()
defer func() {
if rec := recover(); rec != nil {
h.PanicHandler(rec)
}
}()
cp := copyEvent(ev, et)
if h.callMiddlewares(cp, et, gh.middlewares) {
return
}
if gh.once != nil {
gh.once.Do(func() {
h.callHandler(gh, cp)
gh.rm()
})
} else {
h.callHandler(gh, cp)
}
}(gh)
}
}
func (h *EventHandler) callHandler(gh *genericHandler, ev reflect.Value) {
if gh.channel {
gh.handler.TrySend(ev)
} else {
result := gh.handler.Call([]reflect.Value{h.sv, ev})
h.handleResult(result)
}
}
// callGlobalMiddlewares calls the global middlewares using the passed event
// ev.
// ev must be a pointer to the event, and et must be ev's type.
func (h *EventHandler) callGlobalMiddlewares(ev reflect.Value, et reflect.Type) bool {
h.globalMiddlewaresMutex.RLock()
interfaceMiddlewares := h.globalMiddlewares[interfaceType]
baseMiddlewares := h.globalMiddlewares[baseType]
typedMiddlewares := h.globalMiddlewares[et]
h.globalMiddlewaresMutex.RUnlock()
var im, bm, tm int
for {
var (
next globalMiddleware
typ reflect.Type
index *int = nil
)
if im < len(interfaceMiddlewares) {
next = interfaceMiddlewares[im]
typ = et
index = &im
}
if bm < len(baseMiddlewares) && (index == nil || baseMiddlewares[bm].serial < next.serial) {
next = baseMiddlewares[bm]
typ = baseType
index = &bm
}
if tm < len(typedMiddlewares) && (index == nil || typedMiddlewares[tm].serial < next.serial) {
next = typedMiddlewares[tm]
typ = et
index = &tm
}
if index == nil {
break // every middleware consumed
}
var in2 reflect.Value
switch typ {
case et:
in2 = ev
case baseType:
in2 = ev.Elem().FieldByName("Base")
default:
continue // invalid, skip
}
var (
result []reflect.Value
didPanic bool
)
func() {
defer func() {
if rec := recover(); rec != nil {
h.PanicHandler(rec)
didPanic = true
}
}()
result = next.middleware.Call([]reflect.Value{h.sv, in2})
}()
if didPanic {
return true
}
if h.handleResult(result) {
return true
}
*index++
}
return false
}
// callMiddlewares calls the passed slice of middlewares in the passed order.
// ev must not be a pointer, however, et is expected to be the pointerized type
// of ev.
func (h *EventHandler) callMiddlewares(ev reflect.Value, et reflect.Type, middlewares []middleware) bool {
for _, m := range middlewares {
var (
result []reflect.Value
base reflect.Value
)
switch m.typ {
case interfaceType:
result = m.middleware.Call([]reflect.Value{h.sv, ev})
case baseType:
if !base.IsValid() {
base = ev.Elem().FieldByName("Base")
}
result = m.middleware.Call([]reflect.Value{h.sv, base})
case et:
result = m.middleware.Call([]reflect.Value{h.sv, ev})
default: // skip invalid
continue
}
if h.handleResult(result) {
return true
}
}
return false
}
func (h *EventHandler) handleReady(e *ReadyEvent) {
for _, g := range e.Guilds {
// store this so we know when we need to dispatch the corresponding
// GuildReadyEvent
h.s.unreadyGuilds.Add(g.ID)
}
}
func (h *EventHandler) handleGuildCreate(e *GuildCreateEvent) interface{} {
switch {
// this guild was unavailable, but has come back online
case h.s.unavailableGuilds.Delete(e.ID):
return &GuildAvailableEvent{GuildCreateEvent: e}
// the guild was announced in Ready and has now become available
case h.s.unreadyGuilds.Delete(e.ID):
return &GuildReadyEvent{GuildCreateEvent: e}
// we don't know this guild, hence we just joined it
default:
return &GuildJoinEvent{GuildCreateEvent: e}
}
}
func (h *EventHandler) handleGuildDelete(e *GuildDeleteEvent) interface{} {
// store this so we can later dispatch a GuildAvailableEvent, once the
// guild becomes available again.
if e.Unavailable {
h.s.unavailableGuilds.Add(e.ID)
return &GuildUnavailableEvent{GuildDeleteEvent: e}
}
// it might have been unavailable before we left
h.s.unavailableGuilds.Delete(e.ID)
return &GuildLeaveEvent{GuildDeleteEvent: e}
}