add Sprig functions to go templates

fixes #1121

Author: wunter8

go.mod

@@ -31,6 +31,7 @@ require github.com/pkg/errors v0.9.1 // indirect
 
 require (
 	firebase.google.com/go/v4 v4.14.0
+	github.com/Masterminds/sprig/v3 v3.2.3
 	github.com/SherClockHolmes/webpush-go v1.3.0
 	github.com/microcosm-cc/bluemonday v1.0.26
 	github.com/prometheus/client_golang v1.19.1
@@ -45,6 +46,8 @@ require (
 	cloud.google.com/go/iam v1.1.8 // indirect
 	cloud.google.com/go/longrunning v0.5.7 // indirect
 	github.com/AlekSi/pointer v1.2.0 // indirect
+	github.com/Masterminds/goutils v1.1.1 // indirect
+	github.com/Masterminds/semver/v3 v3.2.0 // indirect
 	github.com/MicahParks/keyfunc v1.9.0 // indirect
 	github.com/aymerick/douceur v0.2.0 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
@@ -63,12 +66,18 @@ require (
 	github.com/googleapis/enterprise-certificate-proxy v0.3.2 // indirect
 	github.com/googleapis/gax-go/v2 v2.12.4 // indirect
 	github.com/gorilla/css v1.0.1 // indirect
+	github.com/huandu/xstrings v1.3.3 // indirect
+	github.com/imdario/mergo v0.3.11 // indirect
 	github.com/kr/text v0.2.0 // indirect
+	github.com/mitchellh/copystructure v1.0.0 // indirect
+	github.com/mitchellh/reflectwalk v1.0.0 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.53.0 // indirect
 	github.com/prometheus/procfs v0.14.0 // indirect
 	github.com/russross/blackfriday/v2 v2.1.0 // indirect
+	github.com/shopspring/decimal v1.2.0 // indirect
+	github.com/spf13/cast v1.3.1 // indirect
 	github.com/stretchr/objx v0.5.2 // indirect
 	github.com/xrash/smetrics v0.0.0-20240312152122-5f08fbb34913 // indirect
 	go.opencensus.io v0.24.0 // indirect

server/server.go

@@ -27,6 +27,7 @@ import (
 	"time"
 	"unicode/utf8"
 
+	"github.com/Masterminds/sprig/v3"
 	"github.com/emersion/go-smtp"
 	"github.com/gorilla/websocket"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
@@ -1128,7 +1129,7 @@ func replaceTemplate(tpl string, source string) (string, error) {
 	if err := json.Unmarshal([]byte(source), &data); err != nil {
 		return "", errHTTPBadRequestTemplateMessageNotJSON
 	}
-	t, err := template.New("").Parse(tpl)
+	t, err := template.New("").Funcs(sprig.FuncMap()).Parse(tpl)
 	if err != nil {
 		return "", errHTTPBadRequestTemplateInvalid
 	}

server/server_test.go

@@ -2853,6 +2853,39 @@ template ""}}`,
 	}
 }
 
+func TestServer_MessageTemplate_SprigFunctions(t *testing.T) {
+	t.Parallel()
+	s := newTestServer(t, newTestConfig(t))
+	bodies := []string{
+		`{"foo":"bar","nested":{"title":"here"}}`,
+		`{"topic":"ntfy-test"}`,
+		`{"topic":"another-topic"}`,
+	}
+	templates := []string{
+		`{{.foo | upper}} is {{.nested.title | repeat 3}}`,
+		`{{if hasPrefix "ntfy-" .topic}}Topic: {{trimPrefix "ntfy-" .topic}}{{ else }}Topic: {{.topic}}{{end}}`,
+		`{{if hasPrefix "ntfy-" .topic}}Topic: {{trimPrefix "ntfy-" .topic}}{{ else }}Topic: {{.topic}}{{end}}`,
+	}
+	targets := []string{
+		`BAR is hereherehere`,
+		`Topic: test`,
+		`Topic: another-topic`,
+	}
+	for i, body := range bodies {
+		template := templates[i]
+		target := targets[i]
+		t.Run(template, func(t *testing.T) {
+			response := request(t, s, "PUT", `/mytopic`, body, map[string]string{
+				"Template": "yes",
+				"Message":  template,
+			})
+			require.Equal(t, 200, response.Code)
+			m := toMessage(t, response.Body.String())
+			require.Equal(t, target, m.Message)
+		})
+	}
+}
+
 func newTestConfig(t *testing.T) *Config {
 	conf := NewConfig()
 	conf.BaseURL = "http://127.0.0.1:12345"