From d4ad7752fdc8189b20b743398a848c668022b10e Mon Sep 17 00:00:00 2001
From: Grime <john.m.a.grime@gmail.com>
Date: Wed, 11 Sep 2019 14:41:23 -0500
Subject: [PATCH] Added simple change to allow user detection of services
 *leaving* via TTL=0 in DNS-SD messages

---
 client.go                 | 13 ++++---------
 examples/resolv/client.go |  6 +++++-
 2 files changed, 9 insertions(+), 10 deletions(-)

diff --git a/client.go b/client.go
index 53df90a9..9e808feb 100644
--- a/client.go
+++ b/client.go
@@ -191,8 +191,8 @@ func (c *client) mainloop(ctx context.Context, params *LookupParams) {
 	}
 
 	// Iterate through channels from listeners goroutines
-	var entries, sentEntries map[string]*ServiceEntry
-	sentEntries = make(map[string]*ServiceEntry)
+	var entries map[string]*ServiceEntry
+	sentEntries := make(map[string]uint32)
 	for {
 		select {
 		case <-ctx.Done():
@@ -273,12 +273,7 @@ func (c *client) mainloop(ctx context.Context, params *LookupParams) {
 
 		if len(entries) > 0 {
 			for k, e := range entries {
-				if e.TTL == 0 {
-					delete(entries, k)
-					delete(sentEntries, k)
-					continue
-				}
-				if _, ok := sentEntries[k]; ok {
+				if oldTTL, ok := sentEntries[k]; ok && (e.TTL==oldTTL) {
 					continue
 				}
 
@@ -295,7 +290,7 @@ func (c *client) mainloop(ctx context.Context, params *LookupParams) {
 				// This is also a point to possibly stop probing actively for a
 				// service entry.
 				params.Entries <- e
-				sentEntries[k] = e
+				sentEntries[k] = e.TTL
 				params.disableProbing()
 			}
 			// reset entries
diff --git a/examples/resolv/client.go b/examples/resolv/client.go
index 83186bc4..3ea49544 100644
--- a/examples/resolv/client.go
+++ b/examples/resolv/client.go
@@ -27,7 +27,11 @@ func main() {
 	entries := make(chan *zeroconf.ServiceEntry)
 	go func(results <-chan *zeroconf.ServiceEntry) {
 		for entry := range results {
-			log.Println(entry)
+			if entry.TTL>0 {
+				log.Println("[+]", entry)
+			} else {
+				log.Println("[-]", entry)
+			}
 		}
 		log.Println("No more entries.")
 	}(entries)