// The core ZeroMQ messaging loop. Handles requests and responses
// asynchronously using the router socket. Every request is delegated to
// a goroutine for maximum concurrency.
//
// `gozmq` does currently not support copy-free messages/frames. This
// means that every message passing through this function needs to be
// copied in-memory. If this becomes a bottleneck in the future,
// multiple router sockets can be hooked to this final router to scale
// message copying.
//
// TODO: Make this a type function of `Server` to remove a lot of
// parameters.
func loopServer(estore *eventstore.EventStore, evpubsock, frontend zmq.Socket,
stop chan bool) {
toPoll := zmq.PollItems{
zmq.PollItem{Socket: &frontend, zmq.Events: zmq.POLLIN},
}
pubchan := make(chan eventstore.StoredEvent)
estore.RegisterPublishedEventsChannel(pubchan)
go publishAllSavedEvents(pubchan, evpubsock)
defer close(pubchan)
pollchan := make(chan zmqPollResult)
respchan := make(chan zMsg)
pollCancel := make(chan bool)
defer stopPoller(pollCancel)
go asyncPoll(pollchan, toPoll, pollCancel)
for {
select {
case res := <-pollchan:
if res.err != nil {
log.Println("Could not poll:", res.err)
}
if res.err == nil && toPoll[0].REvents&zmq.POLLIN != 0 {
msg, _ := toPoll[0].Socket.RecvMultipart(0)
zmsg := zMsg(msg)
go handleRequest(respchan, estore, zmsg)
}
go asyncPoll(pollchan, toPoll, pollCancel)
case frames := <-respchan:
if err := frontend.SendMultipart(frames, 0); err != nil {
log.Println(err)
}
case <-stop:
log.Println("Server asked to stop. Stopping...")
return
}
}
}
// Handles a single ZeroMQ RES/REQ loop synchronously.
//
// The full request message stored in `msg` and the full ZeroMQ response
// is pushed to `respchan`. The function does not return any error
// because it is expected to be called asynchronously as a goroutine.
func handleRequest(respchan chan zMsg, estore *eventstore.EventStore, msg zMsg) {
// TODO: Rename to 'framelist'
parts := list.New()
for _, msgpart := range msg {
parts.PushBack(msgpart)
}
resptemplate := list.New()
emptyFrame := zFrame("")
for true {
resptemplate.PushBack(parts.Remove(parts.Front()))
if bytes.Equal(parts.Front().Value.(zFrame), emptyFrame) {
break
}
}
if parts.Len() == 0 {
errstr := "Incoming command was empty. Ignoring it."
log.Println(errstr)
response := copyList(resptemplate)
response.PushBack(zFrame("ERROR " + errstr))
respchan <- listToFrames(response)
return
}
command := string(parts.Front().Value.(zFrame))
switch command {
case "PUBLISH":
parts.Remove(parts.Front())
if parts.Len() != 2 {
// TODO: Constantify this error message
errstr := "Wrong number of frames for PUBLISH."
log.Println(errstr)
response := copyList(resptemplate)
response.PushBack(zFrame("ERROR " + errstr))
respchan <- listToFrames(response)
} else {
estream := parts.Remove(parts.Front())
data := parts.Remove(parts.Front())
newevent := eventstore.Event{
estream.(eventstore.StreamName),
data.(zFrame),
}
newId, err := estore.Add(newevent)
if err != nil {
sErr := err.Error()
log.Println(sErr)
response := copyList(resptemplate)
response.PushBack(zFrame("ERROR " + sErr))
respchan <- listToFrames(response)
} else {
// the event was added
response := copyList(resptemplate)
response.PushBack(zFrame("PUBLISHED"))
response.PushBack(zFrame(newId))
respchan <- listToFrames(response)
}
}
case "QUERY":
parts.Remove(parts.Front())
if parts.Len() != 3 {
// TODO: Constantify this error message
errstr := "Wrong number of frames for QUERY."
log.Println(errstr)
response := copyList(resptemplate)
response.PushBack(zFrame("ERROR " + errstr))
respchan <- listToFrames(response)
} else {
estream := parts.Remove(parts.Front())
fromid := parts.Remove(parts.Front())
toid := parts.Remove(parts.Front())
req := eventstore.QueryRequest{
Stream: estream.(zFrame),
FromId: fromid.(zFrame),
ToId: toid.(zFrame),
}
events, err := estore.Query(req)
if err != nil {
sErr := err.Error()
log.Println(sErr)
response := copyList(resptemplate)
response.PushBack(zFrame("ERROR " + sErr))
respchan <- listToFrames(response)
} else {
for eventdata := range events {
response := copyList(resptemplate)
response.PushBack([]byte("EVENT"))
response.PushBack(eventdata.Id)
response.PushBack(eventdata.Data)
respchan <- listToFrames(response)
}
response := copyList(resptemplate)
response.PushBack(zFrame("END"))
respchan <- listToFrames(response)
}
}
default:
// TODO: Move these error strings out as constants of
// this package.
// TODO: Move the chunk of code below into a separate
// function and reuse for similar piece of code above.
// TODO: Constantify this error message
errstr := "Unknown request type."
log.Println(errstr)
response := copyList(resptemplate)
response.PushBack(zFrame("ERROR " + errstr))
respchan <- listToFrames(response)
}
}
