template/interpolate: timestamp

template/interpolate/funcs.go

@@ -4,15 +4,26 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"strconv"
 	"text/template"
 	"time"
 )
 
+// InitTime is the UTC time when this package was initialized. It is
+// used as the timestamp for all configuration templates so that they
+// match for a single build.
+var InitTime time.Time
+
+func init() {
+	InitTime = time.Now().UTC()
+}
+
 // Funcs are the interpolation funcs that are available within interpolations.
 var FuncGens = map[string]FuncGenerator{
 	"env":       funcGenEnv,
 	"isotime":   funcGenIsotime,
 	"pwd":       funcGenPwd,
+	"timestamp": funcGenTimestamp,
 	"user":      funcGenUser,
 }
 
@@ -63,6 +74,12 @@ func funcGenPwd(ctx *Context) interface{} {
 	}
 }
 
+func funcGenTimestamp(ctx *Context) interface{} {
+	return func() string {
+		return strconv.FormatInt(InitTime.Unix(), 10)
+	}
+}
+
 func funcGenUser(ctx *Context) interface{} {
 	return func() string {
 		return ""

template/interpolate/funcs_test.go

@@ -2,6 +2,7 @@ package interpolate
 
 import (
 	"os"
+	"strconv"
 	"testing"
 	"time"
 )
@@ -114,3 +115,30 @@ func TestFuncPwd(t *testing.T) {
 		}
 	}
 }
+
+func TestFuncTimestamp(t *testing.T) {
+	expected := strconv.FormatInt(InitTime.Unix(), 10)
+
+	cases := []struct {
+		Input  string
+		Output string
+	}{
+		{
+			`{{timestamp}}`,
+			expected,
+		},
+	}
+
+	ctx := &Context{}
+	for _, tc := range cases {
+		i := &I{Value: tc.Input}
+		result, err := i.Render(ctx)
+		if err != nil {
+			t.Fatalf("Input: %s\n\nerr: %s", tc.Input, err)
+		}
+
+		if result != tc.Output {
+			t.Fatalf("Input: %s\n\nGot: %s", tc.Input, result)
+		}
+	}
+}