Merge pull request #5 from blendle/required

add "required" template function

epp/epp.go

@@ -2,6 +2,7 @@ package epp
 
 import (
 	"bytes"
+	"fmt"
 	"text/template"
 
 	"github.com/Masterminds/sprig"
@@ -20,6 +21,17 @@ func Parse(input []byte) ([]byte, error) {
 			}
 			return buf.String(), nil
 		},
+
+		"required": func(warn string, val interface{}) (interface{}, error) {
+			if val == nil {
+				return val, fmt.Errorf(warn)
+			} else if _, ok := val.(string); ok {
+				if val == "" {
+					return val, fmt.Errorf(warn)
+				}
+			}
+			return val, nil
+		},
 	}
 
 	tpl, err := t.Funcs(sprig.TxtFuncMap()).Funcs(funcMap).Parse(string(input))

epp/epp_test.go

@@ -3,6 +3,7 @@ package epp
 import (
 	"fmt"
 	"os"
+	"strings"
 	"testing"
 )
 
@@ -65,3 +66,31 @@ hello WORLD`
 		t.Errorf("bad expansion: expected '%s', got '%s'", expected, res)
 	}
 }
+
+func TestRequired(t *testing.T) {
+	tpl := []byte(`{{ required "undefined" "hello" }}`)
+	expected := `hello`
+
+	res, err := Parse(tpl)
+
+	if err != nil {
+		t.Errorf("unexpected error '%s'", err)
+	}
+
+	if string(res) != expected {
+		t.Errorf("bad expansion: expected '%s', got '%s'", expected, res)
+	}
+}
+
+func TestRequired_Undefined(t *testing.T) {
+	tpl := []byte(`{{ required "undefined" .Undefined }}`)
+	_, err := Parse(tpl)
+
+	if err == nil {
+		t.Fatalf("expected error, got nil")
+	}
+
+	if !strings.Contains(err.Error(), "error calling required: undefined") {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}