remove confusing go-marathon log message

Log message produced by go-marathon was:
time="2017-06-28T09:08:19Z" level=debug msg="listenToSSE(): failed to
handle event: failed to decode the event type, content: , error: EOF"

The fix for this was done in the upstream project of go-marathon
donovanhide/eventsource.

Background is that Marathon periodically sends a \n over the SSE
subscription, in order to keep the connection alive. This was parsed as
empty event by the eventsource and published. go-marathon in turn was
not able to do something with this empty event was producing the log
message above. By getting rid of publishing empty events in the
downstream library, we also get rid of this log message.

glide.lock

@@ -1,5 +1,5 @@
 hash: 4e2a6a4fe84b2843ff946fe56deae17f8c7666e2e6567d8a75f4b0bdd7cb0280
-updated: 2017-06-29T16:47:14.848940186+02:00
+updated: 2017-06-30T11:03:09.025639582+02:00
 imports:
 - name: cloud.google.com/go
   version: 2e6a95edb1071d750f6d7db777bf66cd2997af6c
@@ -172,7 +172,7 @@ imports:
   - store/etcd
   - store/zookeeper
 - name: github.com/donovanhide/eventsource
-  version: 441a03aa37b3329bbb79f43de81914ea18724718
+  version: b8f31a59085e69dd2678cf51840db2ac625cb741
 - name: github.com/eapache/channels
   version: 47238d5aae8c0fefd518ef2bee46290909cf8263
 - name: github.com/eapache/queue

vendor/github.com/donovanhide/eventsource/decoder.go

@@ -35,7 +35,6 @@ func NewDecoder(r io.Reader) *Decoder {
 // Any error occuring mid-event is considered non-graceful and will
 // show up as some other error (most likely io.ErrUnexpectedEOF).
 func (dec *Decoder) Decode() (Event, error) {
-
 	// peek ahead before we start a new event so we can return EOFs
 	_, err := dec.Peek(1)
 	if err == io.ErrUnexpectedEOF {
@@ -45,13 +44,18 @@ func (dec *Decoder) Decode() (Event, error) {
 		return nil, err
 	}
 	pub := new(publication)
+	inDecoding := false
 	for {
 		line, err := dec.ReadString('\n')
 		if err != nil {
 			return nil, err
 		}
-		if line == "\n" {
+		if line == "\n" && inDecoding {
+			// the empty line signals the end of an event
 			break
+		} else if line == "\n" && !inDecoding {
+			// only a newline was sent, so we don't want to publish an empty event but try to read again
+			continue
 		}
 		line = strings.TrimSuffix(line, "\n")
 		if strings.HasPrefix(line, ":") {
@@ -62,6 +66,7 @@ func (dec *Decoder) Decode() (Event, error) {
 		if len(sections) == 2 {
 			value = strings.TrimPrefix(sections[1], " ")
 		}
+		inDecoding = true
 		switch field {
 		case "event":
 			pub.event = value