// parseWait is used to parse the ?wait and ?index query params
// Returns true on error
func parseWait(resp http.ResponseWriter, req *http.Request, b *structs.QueryOptions) bool {
query := req.URL.Query()
if wait := query.Get("wait"); wait != "" {
dur, err := time.ParseDuration(wait)
if err != nil {
resp.WriteHeader(400)
resp.Write([]byte("Invalid wait time"))
return true
}
b.MaxQueryTime = dur
}
if idx := query.Get("index"); idx != "" {
index, err := strconv.ParseUint(idx, 10, 64)
if err != nil {
resp.WriteHeader(400)
resp.Write([]byte("Invalid index"))
return true
}
b.MinQueryIndex = index
}
return false
}
// EventList is used to retrieve the recent list of events
func (s *HTTPServer) EventList(resp http.ResponseWriter, req *http.Request) (interface{}, error) {
// Parse the query options, since we simulate a blocking query
var b structs.QueryOptions
if parseWait(resp, req, &b) {
return nil, nil
}
// Look for a name filter
var nameFilter string
if filt := req.URL.Query().Get("name"); filt != "" {
nameFilter = filt
}
// Lots of this logic is borrowed from consul/rpc.go:blockingRPC
// However we cannot use that directly since this code has some
// slight semantics differences...
var timeout <-chan time.Time
var notifyCh chan struct{}
// Fast path non-blocking
if b.MinQueryIndex == 0 {
goto RUN_QUERY
}
// Restrict the max query time
if b.MaxQueryTime > maxQueryTime {
b.MaxQueryTime = maxQueryTime
}
// Ensure a time limit is set if we have an index
if b.MinQueryIndex > 0 && b.MaxQueryTime == 0 {
b.MaxQueryTime = maxQueryTime
}
// Setup a query timeout
if b.MaxQueryTime > 0 {
timeout = time.After(b.MaxQueryTime)
}
// Setup a notification channel for changes
SETUP_NOTIFY:
if b.MinQueryIndex > 0 {
notifyCh = make(chan struct{}, 1)
s.agent.eventNotify.Wait(notifyCh)
}
RUN_QUERY:
// Get the recent events
events := s.agent.UserEvents()
// Filter the events if necessary
if nameFilter != "" {
for i := 0; i < len(events); i++ {
if events[i].Name != nameFilter {
events = append(events[:i], events[i+1:]...)
i--
}
}
}
// Determine the index
var index uint64
if len(events) == 0 {
// Return a non-zero index to prevent a hot query loop. This
// can be caused by a watch for example when there is no matching
// events.
index = 1
} else {
last := events[len(events)-1]
index = uuidToUint64(last.ID)
}
setIndex(resp, index)
// Check for exact match on the query value. Because
// the index value is not monotonic, we just ensure it is
// not an exact match.
if index > 0 && index == b.MinQueryIndex {
select {
case <-notifyCh:
goto SETUP_NOTIFY
case <-timeout:
}
}
return events, nil
}
// blockingRPC is used for queries that need to wait for a minimum index. This
// is used to block and wait for changes.
func (s *Server) blockingRPC(queryOpts *structs.QueryOptions, queryMeta *structs.QueryMeta,
watch state.Watch, run func() error) error {
var timeout *time.Timer
var notifyCh chan struct{}
// Fast path right to the non-blocking query.
if queryOpts.MinQueryIndex == 0 {
goto RUN_QUERY
}
// Make sure a watch was given if we were asked to block.
if watch == nil {
panic("no watch given for blocking query")
}
// Restrict the max query time, and ensure there is always one.
if queryOpts.MaxQueryTime > maxQueryTime {
queryOpts.MaxQueryTime = maxQueryTime
} else if queryOpts.MaxQueryTime <= 0 {
queryOpts.MaxQueryTime = defaultQueryTime
}
// Apply a small amount of jitter to the request.
queryOpts.MaxQueryTime += randomStagger(queryOpts.MaxQueryTime / jitterFraction)
// Setup a query timeout.
timeout = time.NewTimer(queryOpts.MaxQueryTime)
// Setup the notify channel.
notifyCh = make(chan struct{}, 1)
// Ensure we tear down any watches on return.
defer func() {
timeout.Stop()
watch.Clear(notifyCh)
}()
REGISTER_NOTIFY:
// Register the notification channel. This may be done multiple times if
// we haven't reached the target wait index.
watch.Wait(notifyCh)
RUN_QUERY:
// Update the query metadata.
s.setQueryMeta(queryMeta)
// If the read must be consistent we verify that we are still the leader.
if queryOpts.RequireConsistent {
if err := s.consistentRead(); err != nil {
return err
}
}
// Run the query.
metrics.IncrCounter([]string{"consul", "rpc", "query"}, 1)
err := run()
// Check for minimum query time.
if err == nil && queryMeta.Index > 0 && queryMeta.Index <= queryOpts.MinQueryIndex {
select {
case <-notifyCh:
goto REGISTER_NOTIFY
case <-timeout.C:
}
}
return err
}