plugin/template: Add parseInt template function (#5609)

* plugin/template: Add parseInt template function

Signed-off-by: Erik Johansson <ejohansson@spotify.com>

5 files changed, 116 insertions, 20 deletions

diff --git a/plugin/template/README.md b/plugin/template/README.md
index 55889f7bc..5e14ae24a 100644
--- a/plugin/template/README.md
+++ b/plugin/template/README.md
@@ -54,6 +54,10 @@ Each resource record is a full-featured [Go template](https://golang.org/pkg/tex
 * `.Meta` a function that takes a metadata name and returns the value, if the
   metadata plugin is enabled. For example, `.Meta "kubernetes/client-namespace"`
 
+and the following predefined [template functions](https://golang.org/pkg/text/template#hdr-Functions)
+
+* `parseInt` interprets a string in the given base and bit size. Equivalent to [strconv.ParseUint](https://golang.org/pkg/strconv#ParseUint).
+
 The output of the template must be a [RFC 1035](https://tools.ietf.org/html/rfc1035) style resource record (commonly referred to as a "zone file").
 
 **WARNING** there is a syntactical problem with Go templates and CoreDNS config files. Expressions
@@ -177,6 +181,23 @@ Having templates to map certain PTR/A pairs is a common pattern.
 
 Fallthrough is needed for mixed domains where only some responses are templated.
 
+### Resolve hexadecimal ip pattern using parseInt
+
+~~~ corefile
+. {
+    forward . 8.8.8.8
+
+    template IN A example {
+      match "^ip0a(?P<b>[a-f0-9]{2})(?P<c>[a-f0-9]{2})(?P<d>[a-f0-9]{2})[.]example[.]$"
+      answer "{{ .Name }} 60 IN A 10.{{ parseInt .Group.b 16 8 }}.{{ parseInt .Group.c 16 8 }}.{{ parseInt .Group.d 16 8 }}"
+      fallthrough
+    }
+}
+~~~
+
+An IPv4 address can be expressed in a more compact form using its hexadecimal encoding.
+For example `ip-10-123-123.example.` can instead be expressed as `ip0a7b7b7b.example.`
+
 ### Resolve multiple ip patterns
 
 ~~~ corefile
diff --git a/plugin/template/setup.go b/plugin/template/setup.go
index 44d774b6f..fc6b75165 100644
--- a/plugin/template/setup.go
+++ b/plugin/template/setup.go
@@ -80,7 +80,7 @@ func templateParse(c *caddy.Controller) (handler Handler, err error) {
 					return handler, c.ArgErr()
 				}
 				for _, answer := range args {
-					tmpl, err := gotmpl.New("answer").Parse(answer)
+					tmpl, err := newTemplate("answer", answer)
 					if err != nil {
 						return handler, c.Errf("could not compile template: %s, %v", c.Val(), err)
 					}
@@ -93,7 +93,7 @@ func templateParse(c *caddy.Controller) (handler Handler, err error) {
 					return handler, c.ArgErr()
 				}
 				for _, additional := range args {
-					tmpl, err := gotmpl.New("additional").Parse(additional)
+					tmpl, err := newTemplate("additional", additional)
 					if err != nil {
 						return handler, c.Errf("could not compile template: %s, %v\n", c.Val(), err)
 					}
@@ -106,7 +106,7 @@ func templateParse(c *caddy.Controller) (handler Handler, err error) {
 					return handler, c.ArgErr()
 				}
 				for _, authority := range args {
-					tmpl, err := gotmpl.New("authority").Parse(authority)
+					tmpl, err := newTemplate("authority", authority)
 					if err != nil {
 						return handler, c.Errf("could not compile template: %s, %v\n", c.Val(), err)
 					}
diff --git a/plugin/template/setup_test.go b/plugin/template/setup_test.go
index 39096cc8d..9f03eebcc 100644
--- a/plugin/template/setup_test.go
+++ b/plugin/template/setup_test.go
@@ -83,6 +83,20 @@ func TestSetupParse(t *testing.T) {
 			}`,
 			true,
 		},
+		{
+			`template ANY ANY {
+				answer "{{ notAFunction }}"
+			}`,
+			true,
+		},
+		{
+			`template ANY ANY {
+				answer "{{ parseInt }}"
+				additional "{{ parseInt }}"
+				authority "{{ parseInt }}"
+			}`,
+			false,
+		},
 		// examples
 		{`template ANY ANY (?P<x>`, false},
 		{
@@ -129,6 +143,13 @@ func TestSetupParse(t *testing.T) {
 			false,
 		},
 		{
+			`template IN A example {
+				match ^ip0a(?P<b>[a-f0-9]{2})(?P<c>[a-f0-9]{2})(?P<d>[a-f0-9]{2})[.]example[.]$
+				answer "{{ .Name }} 3600 IN A 10.{{ parseInt .Group.b 16 8 }}.{{ parseInt .Group.c 16 8 }}.{{ parseInt .Group.d 16 8 }}"
+			}`,
+			false,
+		},
+		{
 			`template IN MX example {
 					match ^ip-10-(?P<b>[0-9]*)-(?P<c>[0-9]*)-(?P<d>[0-9]*)[.]example[.]$
 					answer "{{ .Name }} 60 IN MX 10 {{ .Name }}"
diff --git a/plugin/template/template.go b/plugin/template/template.go
index 7b6647109..48e9d6c54 100644
--- a/plugin/template/template.go
+++ b/plugin/template/template.go
@@ -150,6 +150,13 @@ func executeRRTemplate(server, view, section string, template *gotmpl.Template,
 	return rr, nil
 }
 
+func newTemplate(name, text string) (*gotmpl.Template, error) {
+  funcMap := gotmpl.FuncMap{
+    "parseInt": strconv.ParseUint,
+  }
+  return gotmpl.New(name).Funcs(funcMap).Parse(text)
+}
+
 func (t template) match(ctx context.Context, state request.Request) (*templateData, bool, bool) {
 	q := state.Req.Question[0]
 	data := &templateData{md: metadata.ValueFuncs(ctx), Remote: state.IP()}
diff --git a/plugin/template/template_test.go b/plugin/template/template_test.go
index 25e8df748..3587742aa 100644
--- a/plugin/template/template_test.go
+++ b/plugin/template/template_test.go
@@ -19,7 +19,15 @@ import (
 func TestHandler(t *testing.T) {
 	exampleDomainATemplate := template{
 		regex:  []*regexp.Regexp{regexp.MustCompile("(^|[.])ip-10-(?P<b>[0-9]*)-(?P<c>[0-9]*)-(?P<d>[0-9]*)[.]example[.]$")},
-		answer: []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}"))},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}"))},
+		qclass: dns.ClassANY,
+		qtype:  dns.TypeANY,
+		fall:   fall.Root,
+		zones:  []string{"."},
+	}
+	exampleDomainAParseIntTemplate := template{
+		regex:  []*regexp.Regexp{regexp.MustCompile("^ip0a(?P<b>[a-f0-9]{2})(?P<c>[a-f0-9]{2})(?P<d>[a-f0-9]{2})[.]example[.]$")},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }} 60 IN A 10.{{ parseInt .Group.b 16 8 }}.{{ parseInt .Group.c 16 8 }}.{{ parseInt .Group.d 16 8 }}"))},
 		qclass: dns.ClassANY,
 		qtype:  dns.TypeANY,
 		fall:   fall.Root,
@@ -27,7 +35,7 @@ func TestHandler(t *testing.T) {
 	}
 	exampleDomainIPATemplate := template{
 		regex:  []*regexp.Regexp{regexp.MustCompile(".*")},
-		answer: []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("{{ .Name }} 60 IN A {{ .Remote }}"))},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }} 60 IN A {{ .Remote }}"))},
 		qclass: dns.ClassINET,
 		qtype:  dns.TypeA,
 		fall:   fall.Root,
@@ -35,9 +43,9 @@ func TestHandler(t *testing.T) {
 	}
 	exampleDomainANSTemplate := template{
 		regex:      []*regexp.Regexp{regexp.MustCompile("(^|[.])ip-10-(?P<b>[0-9]*)-(?P<c>[0-9]*)-(?P<d>[0-9]*)[.]example[.]$")},
-		answer:     []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}"))},
-		additional: []*gotmpl.Template{gotmpl.Must(gotmpl.New("additional").Parse("ns0.example. IN A 203.0.113.8"))},
-		authority:  []*gotmpl.Template{gotmpl.Must(gotmpl.New("authority").Parse("example. IN NS ns0.example.com."))},
+		answer:     []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}"))},
+		additional: []*gotmpl.Template{gotmpl.Must(newTemplate("additional", "ns0.example. IN A 203.0.113.8"))},
+		authority:  []*gotmpl.Template{gotmpl.Must(newTemplate("authority", "example. IN NS ns0.example.com."))},
 		qclass:     dns.ClassANY,
 		qtype:      dns.TypeANY,
 		fall:       fall.Root,
@@ -45,8 +53,8 @@ func TestHandler(t *testing.T) {
 	}
 	exampleDomainMXTemplate := template{
 		regex:      []*regexp.Regexp{regexp.MustCompile("(^|[.])ip-10-(?P<b>[0-9]*)-(?P<c>[0-9]*)-(?P<d>[0-9]*)[.]example[.]$")},
-		answer:     []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("{{ .Name }} 60 MX 10 {{ .Name }}"))},
-		additional: []*gotmpl.Template{gotmpl.Must(gotmpl.New("additional").Parse("{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}"))},
+		answer:     []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }} 60 MX 10 {{ .Name }}"))},
+		additional: []*gotmpl.Template{gotmpl.Must(newTemplate("additional", "{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}"))},
 		qclass:     dns.ClassANY,
 		qtype:      dns.TypeANY,
 		fall:       fall.Root,
@@ -55,7 +63,7 @@ func TestHandler(t *testing.T) {
 	invalidDomainTemplate := template{
 		regex:  []*regexp.Regexp{regexp.MustCompile("[.]invalid[.]$")},
 		rcode:  dns.RcodeNameError,
-		answer: []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("invalid. 60 {{ .Class }} SOA a.invalid. b.invalid. (1 60 60 60 60)"))},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "invalid. 60 {{ .Class }} SOA a.invalid. b.invalid. (1 60 60 60 60)"))},
 		qclass: dns.ClassANY,
 		qtype:  dns.TypeANY,
 		fall:   fall.Root,
@@ -71,7 +79,15 @@ func TestHandler(t *testing.T) {
 	}
 	brokenTemplate := template{
 		regex:  []*regexp.Regexp{regexp.MustCompile("[.]example[.]$")},
-		answer: []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("{{ .Name }} 60 IN TXT \"{{ index .Match 2 }}\""))},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }} 60 IN TXT \"{{ index .Match 2 }}\""))},
+		qclass: dns.ClassANY,
+		qtype:  dns.TypeANY,
+		fall:   fall.Root,
+		zones:  []string{"."},
+	}
+	brokenParseIntTemplate := template{
+		regex:  []*regexp.Regexp{regexp.MustCompile("[.]example[.]$")},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }} 60 IN TXT \"{{ parseInt \"gg\" 16 8 }}\""))},
 		qclass: dns.ClassANY,
 		qtype:  dns.TypeANY,
 		fall:   fall.Root,
@@ -79,7 +95,7 @@ func TestHandler(t *testing.T) {
 	}
 	nonRRTemplate := template{
 		regex:  []*regexp.Regexp{regexp.MustCompile("[.]example[.]$")},
-		answer: []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("{{ .Name }}"))},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }}"))},
 		qclass: dns.ClassANY,
 		qtype:  dns.TypeANY,
 		fall:   fall.Root,
@@ -87,7 +103,7 @@ func TestHandler(t *testing.T) {
 	}
 	nonRRAdditionalTemplate := template{
 		regex:      []*regexp.Regexp{regexp.MustCompile("[.]example[.]$")},
-		additional: []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("{{ .Name }}"))},
+		additional: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }}"))},
 		qclass:     dns.ClassANY,
 		qtype:      dns.TypeANY,
 		fall:       fall.Root,
@@ -95,7 +111,7 @@ func TestHandler(t *testing.T) {
 	}
 	nonRRAuthoritativeTemplate := template{
 		regex:     []*regexp.Regexp{regexp.MustCompile("[.]example[.]$")},
-		authority: []*gotmpl.Template{gotmpl.Must(gotmpl.New("authority").Parse("{{ .Name }}"))},
+		authority: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "{{ .Name }}"))},
 		qclass:    dns.ClassANY,
 		qtype:     dns.TypeANY,
 		fall:      fall.Root,
@@ -103,7 +119,7 @@ func TestHandler(t *testing.T) {
 	}
 	cnameTemplate := template{
 		regex:  []*regexp.Regexp{regexp.MustCompile("example[.]net[.]")},
-		answer: []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse("example.net 60 IN CNAME target.example.com"))},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", "example.net 60 IN CNAME target.example.com"))},
 		qclass: dns.ClassANY,
 		qtype:  dns.TypeANY,
 		fall:   fall.Root,
@@ -111,9 +127,9 @@ func TestHandler(t *testing.T) {
 	}
 	mdTemplate := template{
 		regex:      []*regexp.Regexp{regexp.MustCompile("(^|[.])ip-10-(?P<b>[0-9]*)-(?P<c>[0-9]*)-(?P<d>[0-9]*)[.]example[.]$")},
-		answer:     []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse(`{{ .Meta "foo" }}-{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}`))},
-		additional: []*gotmpl.Template{gotmpl.Must(gotmpl.New("additional").Parse(`{{ .Meta "bar" }}.example. IN A 203.0.113.8`))},
-		authority:  []*gotmpl.Template{gotmpl.Must(gotmpl.New("authority").Parse(`example. IN NS {{ .Meta "bar" }}.example.com.`))},
+		answer:     []*gotmpl.Template{gotmpl.Must(newTemplate("answer", `{{ .Meta "foo" }}-{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}`))},
+		additional: []*gotmpl.Template{gotmpl.Must(newTemplate("additional", `{{ .Meta "bar" }}.example. IN A 203.0.113.8`))},
+		authority:  []*gotmpl.Template{gotmpl.Must(newTemplate("authority", `example. IN NS {{ .Meta "bar" }}.example.com.`))},
 		qclass:     dns.ClassANY,
 		qtype:      dns.TypeANY,
 		fall:       fall.Root,
@@ -121,7 +137,7 @@ func TestHandler(t *testing.T) {
 	}
 	mdMissingTemplate := template{
 		regex:  []*regexp.Regexp{regexp.MustCompile("(^|[.])ip-10-(?P<b>[0-9]*)-(?P<c>[0-9]*)-(?P<d>[0-9]*)[.]example[.]$")},
-		answer: []*gotmpl.Template{gotmpl.Must(gotmpl.New("answer").Parse(`{{ .Meta "foofoo" }}{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}`))},
+		answer: []*gotmpl.Template{gotmpl.Must(newTemplate("answer", `{{ .Meta "foofoo" }}{{ .Name }} 60 IN A 10.{{ .Group.b }}.{{ .Group.c }}.{{ .Group.d }}`))},
 		qclass: dns.ClassANY,
 		qtype:  dns.TypeANY,
 		fall:   fall.Root,
@@ -243,6 +259,37 @@ func TestHandler(t *testing.T) {
 			},
 		},
 		{
+			name:   "ExampleDomainMatchHexIp",
+			tmpl:   exampleDomainAParseIntTemplate,
+			qclass: dns.ClassINET,
+			qtype:  dns.TypeA,
+			qname:  "ip0a5f0c09.example.",
+			verifyResponse: func(r *dns.Msg) error {
+				if len(r.Answer) != 1 {
+					return fmt.Errorf("expected 1 answer, got %v", len(r.Answer))
+				}
+				if r.Answer[0].Header().Rrtype != dns.TypeA {
+					return fmt.Errorf("expected an A record answer, got %v", dns.TypeToString[r.Answer[0].Header().Rrtype])
+				}
+				if r.Answer[0].(*dns.A).A.String() != "10.95.12.9" {
+					return fmt.Errorf("expected an A record for 10.95.12.9, got %v", r.Answer[0].String())
+				}
+				return nil
+			},
+		},
+		{
+			name:         "BrokenParseIntTemplate",
+			tmpl:         brokenParseIntTemplate,
+			qclass:       dns.ClassINET,
+			qtype:        dns.TypeANY,
+			qname:        "test.example.",
+			expectedCode: dns.RcodeServerFailure,
+			expectedErr: "template: answer:1:26: executing \"answer\" at <parseInt \"gg\" 16 8>: error calling parseInt: strconv.ParseUint: parsing \"gg\": invalid syntax",
+			verifyResponse: func(r *dns.Msg) error {
+				return nil
+			},
+		},
+		{
 			name:   "ExampleDomainMXMatch",
 			tmpl:   exampleDomainMXTemplate,
 			qclass: dns.ClassINET,