Do not do ddns update if ip is same

4 files changed, 77 insertions, 2 deletions

diff --git a/.gitignore b/.gitignore
index 75c9781..0b56a16 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
-./dns-service
+/dns-service
 
 # Generated files have a zzz_ prefix
 **/zzz_*.go
diff --git a/dns/cilent.go b/dns/client.go
index 6efe1b5..f322b45 100644
--- a/dns/cilent.go
+++ b/dns/client.go
@@ -49,6 +49,37 @@ func (c *DNSClient) AXFR(zone *bind.Zone) (chan *dns.Envelope, error) {
         return t.In(m, fmt.Sprintf("%s:53", c.Server))
 }
 
+func (c *DNSClient) ReadRemoteZone(zone *bind.Zone) ([]RR, error) {
+        rrs := []RR{}
+        seenSoa := false
+
+        data, err := c.AXFR(zone)
+        if err != nil {
+                return nil, err
+        }
+
+        for rd := range data {
+                for _, r := range rd.RR {
+                        switch dr := FromDNS(r).(type) {
+                        case *SOA:
+                                // Transfers have 2 SOA records, exclude the last one
+                                if !seenSoa {
+                                        rrs = append(rrs, dr)
+                                        seenSoa = true
+                                }
+                        case RR:
+                                rrs = append(rrs, dr)
+                        default:
+                                // This should only be possible if we somehow are
+                                // missing generated DNS data types.
+                                return nil, fmt.Errorf("Invalid return type")
+                        }
+                }
+        }
+
+        return rrs, nil
+}
+
 func (c *DNSClient) StartUpdate(zone *bind.Zone) *DNSTransaction {
         m := &dns.Msg{}
         m.SetUpdate(zone.Name)
@@ -60,6 +91,18 @@ func (c *DNSClient) StartUpdate(zone *bind.Zone) *DNSTransaction {
         }
 }
 
+func (c *DNSClient) QueryRecursive(zone *bind.Zone, fqdn string, rtype uint16) *DNSTransaction {
+        m := &dns.Msg{}
+        m.RecursionDesired = true
+        m.SetQuestion(fqdn, rtype)
+
+        return &DNSTransaction{
+                zone: zone,
+                key:  zone.Keys()[0],
+                msg:  m,
+        }
+}
+
 func (c *DNSClient) SendUpdate(t *DNSTransaction) error {
         udp := &dns.Client{Net: "udp", TsigSecret: t.key.AsMap()}
         tcp := &dns.Client{Net: "tcp", TsigSecret: t.key.AsMap()}
@@ -79,3 +122,23 @@ func (c *DNSClient) SendUpdate(t *DNSTransaction) error {
 
         return nil
 }
+
+func (c *DNSClient) SendQuery(t *DNSTransaction) ([]dns.RR, error) {
+        udp := &dns.Client{Net: "udp", TsigSecret: t.key.AsMap()}
+        tcp := &dns.Client{Net: "tcp", TsigSecret: t.key.AsMap()}
+
+        t.msg.SetEdns0(4096, false)
+        t.key.Sign(t.msg)
+
+        in, _, err := udp.Exchange(t.msg, c.Server)
+        if in != nil && in.Truncated {
+                // If the TCP request succeeds, the err will reset to nil
+                in, _, err = tcp.Exchange(t.msg, c.Server)
+        }
+
+        if err != nil {
+                return nil, err
+        }
+
+        return in.Answer, nil
+}
diff --git a/go.sum b/go.sum
index fbb01ae..89417d5 100644
--- a/go.sum
+++ b/go.sum
@@ -70,6 +70,7 @@ golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20190923162816-aa69164e4478 h1:l5EDrHhldLYb3ZRHDUhXF7Om7MvYXnkV9/iQNo1lX6g=
 golang.org/x/net v0.0.0-20190923162816-aa69164e4478/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58 h1:8gQV6CLnAEikrhgkHFbMAEhagSSnXWGV915qUMm9mrU=
 golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
 golang.org/x/sys v0.0.0-20181205085412-a5c9d58dba9a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
diff --git a/web/controllers/ddns.go b/web/controllers/ddns.go
index 692b59f..d476255 100644
--- a/web/controllers/ddns.go
+++ b/web/controllers/ddns.go
@@ -5,6 +5,7 @@ import (
         "net/http"
 
         "github.com/gin-gonic/gin"
+        godns "github.com/miekg/dns"
 
         "code.crute.me/mcrute/go_ddns_manager/dns"
         "code.crute.me/mcrute/go_ddns_manager/util"
@@ -35,7 +36,17 @@ func UpdateDynamicDNS(c *gin.Context) {
                 return
         }
 
-        txn := cfg.DNSClient.StartUpdate(zone).Upsert(&dns.A{
+        txn := cfg.DNSClient.QueryRecursive(zone, res, godns.TypeA)
+        cur, err := cfg.DNSClient.SendQuery(txn)
+        if err == nil && len(cur) == 1 {
+                if cur[0].(*godns.A).A.Equal(inip) {
+                        log.Printf("ddns: Update not required for '%s', IP %s", res, inip)
+                        c.String(http.StatusNotModified, "")
+                        return
+                }
+        }
+
+        txn = cfg.DNSClient.StartUpdate(zone).Upsert(&dns.A{
                 Name: part,
                 Ttl:  60,
                 A:    inip,