Implementation of change detection

If there is an update in discovery an function is triggered
that can pick it up.

daemon/main.go

@@ -137,12 +137,39 @@ func main() {
 	// Server discovering stuff
 	// ------------------------
 
-	// Connect to the NATS service
+	// Setup callback function to register and unregister discovery packets from other servers
 	driver.RegisterSubscribeFunction(func(d server.Discovery) {
+		// Check if the local version and the new version are somehow changed
+		localVersion := discoveryStorage.Get(d.Hostname)
+		exists := discoveryStorage.Exist(d.Hostname)
+		changed := server.Compare(localVersion, d)
+
 		discoveryStorage.Add(d)
+
+		if changed {
+
+			// Print this only if the server is already registered
+			if exists {
+				log.Printf("%s has been updated", d.Hostname)
+			}
+
+			go func() {
+				err = discoveryChange(d)
+				if err != nil {
+					log.Printf("discovery changed error: %v", err)
+				}
+			}()
+		}
+
 	})
 	driver.RegisterUnsubscribeFunction(func(d server.Discovery) {
 		discoveryStorage.Delete(d.Hostname)
+		go func() {
+			err = discoveryChange(d)
+			if err != nil {
+				log.Printf("discovery changed error: %v", err)
+			}
+		}()
 	})
 
 	err = driver.Init()

daemon/update.go

@@ -0,0 +1,14 @@
+package main
+
+import (
+	"github.com/by-cx/lobby/server"
+)
+
+// These functions are called when something has changed in the storage
+
+// discoveryChange is called when daemon detects that a newly arrived discovery
+// packet is somehow different than the localone. This can be used to trigger
+// some action in the local machine.
+func discoveryChange(discovery server.Discovery) error {
+	return nil
+}

go.mod

@@ -7,6 +7,7 @@ require (
 	github.com/fatih/color v1.12.0
 	github.com/go-redis/redis v6.15.9+incompatible
 	github.com/go-resty/resty/v2 v2.6.0
+	github.com/google/go-cmp v0.5.5
 	github.com/kelseyhightower/envconfig v1.4.0
 	github.com/labstack/echo v3.3.10+incompatible
 	github.com/labstack/gommon v0.3.0 // indirect

go.sum

@@ -31,6 +31,7 @@ github.com/golang/snappy v0.0.3/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEW
 github.com/google/go-cmp v0.3.0/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.3.1/go.mod h1:8QqcDgzrUqlUb/G2PQTWiueGozuR1884gddMywk6iLU=
 github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
 github.com/kelseyhightower/envconfig v1.4.0 h1:Im6hONhd3pLkfDFsbRgu68RDNkGF1r3dvMUtDTo2cv8=
@@ -148,6 +149,7 @@ golang.org/x/tools v0.0.0-20201224043029-2b0845dc783e/go.mod h1:emZCQorbCU4vsT4f
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 h1:go1bK/D/BFZV2I8cIQd1NKEZ+0owSTG1fDTci4IqFcE=
 golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 google.golang.org/protobuf v0.0.0-20200109180630-ec00e32a8dfd/go.mod h1:DFci5gLYBciE7Vtevhsrf46CRTquxDuWsQurQQe4oz8=
 google.golang.org/protobuf v0.0.0-20200221191635-4d8936d0db64/go.mod h1:kwYJMbMJ01Woi6D6+Kah6886xMZcty6N08ah7+eCXa0=

server/tools.go

@@ -0,0 +1,12 @@
+package server
+
+import "github.com/google/go-cmp/cmp"
+
+// Compare compares discovery A and B and returns true if those two are different.
+func Compare(discoveryA, discoveryB Discovery) bool {
+	discoveryA.LastCheck = 0
+	discoveryB.LastCheck = 0
+	discoveryA.TTL = 0
+	discoveryB.TTL = 0
+	return !cmp.Equal(discoveryA, discoveryB)
+}

server/tools_test.go

@@ -0,0 +1,45 @@
+package server
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCompare(t *testing.T) {
+	discoveryA := Discovery{
+		Hostname: "abcd.com",
+		Labels: Labels{
+			Label("label1"),
+		},
+		LastCheck: 52,
+	}
+	discoveryAB := Discovery{
+		Hostname: "abcd.com",
+		Labels: Labels{
+			Label("label1"),
+		},
+		LastCheck: 56,
+	}
+	discoveryB := Discovery{
+		Hostname: "efgh.com",
+		Labels: Labels{
+			Label("label2"),
+		},
+		LastCheck: 56,
+	}
+	discoveryC := Discovery{
+		Hostname: "abcd.com",
+		Labels: Labels{
+			Label("label2"),
+		},
+		LastCheck: 60,
+	}
+
+	assert.True(t, Compare(discoveryA, discoveryB))
+	assert.True(t, Compare(discoveryB, discoveryC))
+	assert.True(t, Compare(discoveryA, discoveryC)) // Test different labels and same hostname
+	assert.False(t, Compare(discoveryA, discoveryA))
+	assert.False(t, Compare(discoveryB, discoveryB))
+	assert.False(t, Compare(discoveryA, discoveryAB)) // Test that last check is zeroed
+}

server/types.go

@@ -1,5 +1,7 @@
 package server
 
+import "strings"
+
 // Label keeps one piece of information about a single server
 type Label string
 
@@ -7,6 +9,34 @@ func (l Label) String() string {
 	return string(l)
 }
 
+// GetPart returns specific part of the label, if part index is higher than last available index it returns empty string.
+func (l Label) GetPart(idx int) string {
+	parts := strings.Split(l.String(), ":")
+
+	if idx < 0 {
+		return ""
+	}
+	if len(parts) >= idx {
+		return ""
+	}
+
+	return parts[idx]
+}
+
+// GetPart1 is exactly same as GetPart but it splits the label only once, this is good for IPv6 addresses
+func (l Label) GetPart1(idx int) string {
+	parts := strings.SplitN(l.String(), ":", 2)
+
+	if idx < 0 {
+		return ""
+	}
+	if len(parts) >= idx {
+		return ""
+	}
+
+	return parts[idx]
+}
+
 // Labels stores multiple Label records
 type Labels []Label