fix: display german umlauts correctly in emails

modules/escaper/escaper.go

@@ -0,0 +1,16 @@
+package escaper
+
+import "strings"
+
+var htmlEntitesEscaper = strings.NewReplacer(
+	`Ä`, "Ä",
+	`ä`, "ä",
+	`Ö`, "Ö",
+	`ö`, "ö",
+	`Ü`, "Ü",
+	`ü`, "ü",
+)
+
+func EscapeHtmlEntites(s string) string {
+	return htmlEntitesEscaper.Replace(s)
+}

modules/structs/mail.go

@@ -2,12 +2,14 @@ package structs
 
 import (
 	"bytes"
+	"encoding/base64"
 	"html/template"
 	"net/smtp"
 	"strings"
 
 	"clickandjoin.app/emailserver/modules/cache"
 	"clickandjoin.app/emailserver/modules/config"
+	"clickandjoin.app/emailserver/modules/escaper"
 	"github.com/sirupsen/logrus"
 )
 
@@ -70,10 +72,21 @@ func (m *Mail) RenderTemplate() (string, error) {
 				v = value[config.Cfg.DefaultLanguageCode]
 			}
 
+			// escaping so that umlauts are displayed correctly
+			if m.LanguageId == "de" {
+				v = escaper.EscapeHtmlEntites(v)
+			}
+
 			body = []byte(strings.Replace(string(body), "%"+key+"%", v, -1))
 		}
 	}
 
+	// The subject line of an email is an independent header and utf 8 must be set for it
+	// https://ncona.com/2011/06/using-utf-8-characters-on-an-e-mail-subject/
+	if m.LanguageId == "de" {
+		m.Subject = "=?utf-8?B?" + base64.StdEncoding.EncodeToString([]byte(m.Subject)) + "?="
+	}
+
 	t := template.Must(template.New("").Parse(string(body)))
 
 	buf := new(bytes.Buffer)