feat: additional template functions

docs/tutorials/nodes.md

@@ -6,6 +6,7 @@ Using nodes (`--source=node`) as source is possible to synchronize a DNS zone wi
 The node source adds an `A` record per each node `externalIP` (if not found, any IPv4 `internalIP` is used instead).
 It also adds an `AAAA` record per each node IPv6 `internalIP`.
 The TTL of the records can be set with the `external-dns.alpha.kubernetes.io/ttl` node annotation.
+The FQDN template provides more than 100+ functions, documented [here](https://go-task.github.io/slim-sprig/). For instance, it includes a function to replace all `.` with `-` in the node name, which can be useful with cloud providers that include dots in the node name. There are two additional functions available on top of the standard sprig functions: `isIPv4` and `isIPv6`. The functions can be used to test a string for being an IPv4 or IPv6 address.
 
 ## Manifest (for cluster without RBAC enabled)
 
@@ -37,7 +38,7 @@ spec:
         - --domain-filter=external-dns-test.my-org.com
         - --aws-zone-type=public
         - --registry=txt
-        - --fqdn-template={{.Name}}.external-dns-test.my-org.com
+        - --fqdn-template={{.Name | replace "." "-"}}.external-dns-test.my-org.com
         - --txt-owner-id=my-identifier
         - --policy=sync
         - --log-level=debug
@@ -108,7 +109,7 @@ spec:
         - --domain-filter=external-dns-test.my-org.com
         - --aws-zone-type=public
         - --registry=txt
-        - --fqdn-template={{.Name}}.external-dns-test.my-org.com
+        - --fqdn-template={{.Name | replace "." "-"}}.external-dns-test.my-org.com
         - --txt-owner-id=my-identifier
         - --policy=sync
         - --log-level=debug

go.mod

@@ -30,6 +30,7 @@ require (
 	github.com/ffledgling/pdns-go v0.0.0-20180219074714-524e7daccd99
 	github.com/go-gandi/go-gandi v0.7.0
 	github.com/go-logr/logr v1.4.2
+	github.com/go-task/slim-sprig v0.0.0-20230315185526-52ccab3ef572
 	github.com/google/go-cmp v0.6.0
 	github.com/google/uuid v1.6.0
 	github.com/gophercloud/gophercloud v1.12.0

go.sum

@@ -433,6 +433,7 @@ github.com/go-sql-driver/mysql v1.4.1/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG
 github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=
 github.com/go-task/slim-sprig v0.0.0-20210107165309-348f09dbbbc0/go.mod h1:fyg7847qk6SyHyPtNmDHnmrv/HOrqktSC+C9fM+CJOE=
 github.com/go-task/slim-sprig v0.0.0-20230315185526-52ccab3ef572 h1:tfuBGBXKqDEevZMzYi5KSi8KkcZtzBcTgAUUtapy0OI=
+github.com/go-task/slim-sprig v0.0.0-20230315185526-52ccab3ef572/go.mod h1:9Pwr4B2jHnOSGXyyzV8ROjYa2ojvAY6HCGYYfMoC3Ls=
 github.com/go-task/slim-sprig/v3 v3.0.0 h1:sUs3vkvUymDpBKi3qH1YSqBQk9+9D/8M2mN1vB6EwHI=
 github.com/go-task/slim-sprig/v3 v3.0.0/go.mod h1:W848ghGpv3Qj3dhTPRyJypKRiqCdHZiAzKg9hl15HA8=
 github.com/gobs/pretty v0.0.0-20180724170744-09732c25a95b h1:/vQ+oYKu+JoyaMPDsv5FzwuL2wwWBgBbtj/YLCi4LuA=

source/node_test.go

@@ -61,6 +61,11 @@ func testNodeSourceNewNodeSource(t *testing.T) {
 			expectError:  false,
 			fqdnTemplate: "{{.Name}}-{{.Namespace}}.ext-dns.test.com",
 		},
+		{
+			title:        "complex template",
+			expectError:  false,
+			fqdnTemplate: "{{range .Status.Addresses}}{{if and (eq .Type \"ExternalIP\") (isIPv4 .Address)}}{{.Address | replace \".\" \"-\"}}{{break}}{{end}}{{end}}.ext-dns.test.com",
+		},
 		{
 			title:            "non-empty annotation filter label",
 			expectError:      false,

source/source.go

@@ -29,6 +29,7 @@ import (
 	"time"
 	"unicode"
 
+	sprig "github.com/go-task/slim-sprig"
 	log "github.com/sirupsen/logrus"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/labels"
@@ -147,9 +148,11 @@ func parseTemplate(fqdnTemplate string) (tmpl *template.Template, err error) {
 	if fqdnTemplate == "" {
 		return nil, nil
 	}
-	funcs := template.FuncMap{
-		"trimPrefix": strings.TrimPrefix,
-	}
+
+	funcs := sprig.HermeticTxtFuncMap()
+	funcs["isIPv6"] = isIPv6String
+	funcs["isIPv4"] = isIPv4String
+
 	return template.New("endpoint").Funcs(funcs).Parse(fqdnTemplate)
 }
 
@@ -393,3 +396,8 @@ func isIPv6String(ip string) bool {
 	netIP := net.ParseIP(ip)
 	return netIP != nil && netIP.To4() == nil
 }
+
+func isIPv4String(input string) bool {
+	netIP := net.ParseIP(input)
+	return netIP != nil && netIP.To4() != nil && !strings.Contains(input, ":")
+}