// This is the core functionality of both the HTTP and WebSocket-based continuous change feed.
// It defers to a callback function 'send()' to actually send the changes to the client.
// It will call send(nil) to notify that it's caught up and waiting for new changes, or as
// a periodic heartbeat while waiting.
func (h *handler) generateContinuousChanges(inChannels base.Set, options db.ChangesOptions, send func([]*db.ChangeEntry) error) error {
// Set up heartbeat/timeout
var timeoutInterval time.Duration
var timer *time.Timer
var heartbeat <-chan time.Time
if ms := h.getRestrictedIntQuery("heartbeat", 0, kMinHeartbeatMS, 0); ms > 0 {
ticker := time.NewTicker(time.Duration(ms) * time.Millisecond)
defer ticker.Stop()
heartbeat = ticker.C
} else if ms := h.getRestrictedIntQuery("timeout", kDefaultTimeoutMS, 0, kMaxTimeoutMS); ms > 0 {
timeoutInterval = time.Duration(ms) * time.Millisecond
defer func() {
if timer != nil {
timer.Stop()
}
}()
}
options.Wait = true // we want the feed channel to wait for changes
options.Continuous = true // and to keep sending changes indefinitely
var lastSeqID string
var feed <-chan *db.ChangeEntry
var timeout <-chan time.Time
var err error
loop:
for {
if feed == nil {
// Refresh the feed of all current changes:
if lastSeqID != "" { // start after end of last feed
options.Since = channels.TimedSetFromString(lastSeqID)
}
feed, err = h.db.MultiChangesFeed(inChannels, options)
if err != nil || feed == nil {
return err
}
}
if timeoutInterval > 0 && timer == nil {
// Timeout resets after every change is sent
timer = time.NewTimer(timeoutInterval)
timeout = timer.C
}
// Wait for either a new change, a heartbeat, or a timeout:
select {
case entry, ok := <-feed:
if !ok {
feed = nil
} else if entry == nil {
err = send(nil)
} else {
entries := []*db.ChangeEntry{entry}
waiting := false
// Batch up as many entries as we can without waiting:
collect:
for len(entries) < 20 {
select {
case entry, ok = <-feed:
if !ok {
feed = nil
break collect
} else if entry == nil {
waiting = true
break collect
}
entries = append(entries, entry)
default:
break collect
}
}
base.LogTo("Changes", "sending %d change(s)", len(entries))
err = send(entries)
if err == nil && waiting {
err = send(nil)
}
lastSeqID = entries[len(entries)-1].Seq
if options.Limit > 0 {
if len(entries) >= options.Limit {
break loop
}
options.Limit -= len(entries)
}
}
// Reset the timeout after sending an entry:
if timer != nil {
timer.Stop()
timer = nil
}
case <-heartbeat:
err = send(nil)
case <-timeout:
break loop
}
if err != nil {
h.logStatus(http.StatusOK, fmt.Sprintf("Write error: %v", err))
return nil // error is probably because the client closed the connection
}
}
h.logStatus(http.StatusOK, "OK (continuous feed closed)")
return nil
}
