// Call invokes a delayed function.
// f.Call(c, ...)
// is equivalent to
// t, _ := f.Task(...)
// taskqueue.Add(c, t, "")
func (f *Function) Call(c appengine.Context, args ...interface{}) {
t, err := f.Task(args...)
if err != nil {
c.Errorf("%v", err)
return
}
if _, err := taskqueueAdder(c, t, queue); err != nil {
c.Errorf("delay: taskqueue.Add failed: %v", err)
return
}
}
// FetchToken fetches a new access token for the provided scopes.
// Tokens are cached locally and also with Memcache so that the app can scale
// without hitting quota limits by calling appengine.AccessToken too frequently.
func makeAppEngineTokenFetcher(ctx appengine.Context, opts *oauth2.Options) func(*oauth2.Token) (*oauth2.Token, error) {
return func(existing *oauth2.Token) (*oauth2.Token, error) {
mu.Lock()
defer mu.Unlock()
key := ":" + strings.Join(opts.Scopes, "_")
now := time.Now().Add(safetyMargin)
if t, ok := tokens[key]; ok && !t.Expiry.Before(now) {
return t, nil
}
delete(tokens, key)
// Attempt to get token from Memcache
tok := new(oauth2.Token)
_, err := memcacheGob.Get(ctx, key, tok)
if err == nil && !tok.Expiry.Before(now) {
tokens[key] = tok // Save token locally
return tok, nil
}
token, expiry, err := accessTokenFunc(ctx, opts.Scopes...)
if err != nil {
return nil, err
}
t := &oauth2.Token{
AccessToken: token,
Expiry: expiry,
}
tokens[key] = t
// Also back up token in Memcache
if err = memcacheGob.Set(ctx, &memcache.Item{
Key: key,
Value: []byte{},
Object: *t,
Expiration: expiry.Sub(now),
}); err != nil {
ctx.Errorf("unexpected memcache.Set error: %v", err)
}
return t, nil
}
}
func runFunc(c appengine.Context, w http.ResponseWriter, req *http.Request) {
defer req.Body.Close()
var inv invocation
if err := gob.NewDecoder(req.Body).Decode(&inv); err != nil {
c.Errorf("delay: failed decoding task payload: %v", err)
c.Warningf("delay: dropping task")
return
}
f := funcs[inv.Key]
if f == nil {
c.Errorf("delay: no func with key %q found", inv.Key)
c.Warningf("delay: dropping task")
return
}
ft := f.fv.Type()
in := []reflect.Value{reflect.ValueOf(c)}
for _, arg := range inv.Args {
var v reflect.Value
if arg != nil {
v = reflect.ValueOf(arg)
} else {
// Task was passed a nil argument, so we must construct
// the zero value for the argument here.
n := len(in) // we're constructing the nth argument
var at reflect.Type
if !ft.IsVariadic() || n < ft.NumIn()-1 {
at = ft.In(n)
} else {
at = ft.In(ft.NumIn() - 1).Elem()
}
v = reflect.Zero(at)
}
in = append(in, v)
}
out := f.fv.Call(in)
if n := ft.NumOut(); n > 0 && ft.Out(n-1) == errorType {
if errv := out[n-1]; !errv.IsNil() {
c.Errorf("delay: func failed (will retry): %v", errv.Interface())
w.WriteHeader(http.StatusInternalServerError)
return
}
}
}