From 9c63736489569adf07537b9b01dc5e84f23f9651 Mon Sep 17 00:00:00 2001
From: Christian Schwarz <me@cschwarz.com>
Date: Tue, 14 May 2024 19:18:22 +0200
Subject: [PATCH] treat empty `jobs` & empty YAML as valid & ship empty `jobs`
 in deb/rpm (#788)

fixes https://github.com/zrepl/zrepl/issues/784
obsoletes https://github.com/zrepl/zrepl/pull/787
---
 config/config.go                    | 25 ++++++++++---------------
 config/config_minimal_test.go       | 10 +---------
 config/config_test.go               | 19 ++++++++++++++++++-
 config/samples/empty.yml            |  0
 packaging/systemd-default-zrepl.yml |  4 +---
 5 files changed, 30 insertions(+), 28 deletions(-)
 create mode 100644 config/samples/empty.yml

diff --git a/config/config.go b/config/config.go
index 6c56cc3..f4b84c0 100644
--- a/config/config.go
+++ b/config/config.go
@@ -5,7 +5,6 @@ import (
 	"io/ioutil"
 	"log/syslog"
 	"os"
-	"reflect"
 	"time"
 
 	"github.com/pkg/errors"
@@ -24,7 +23,7 @@ const (
 )
 
 type Config struct {
-	Jobs   []JobEnum `yaml:"jobs"`
+	Jobs   []JobEnum `yaml:"jobs,optional"`
 	Global *Global   `yaml:"global,optional,fromdefaults"`
 }
 
@@ -299,18 +298,6 @@ type Global struct {
 	Serve      *GlobalServe           `yaml:"serve,optional,fromdefaults"`
 }
 
-func Default(i interface{}) {
-	v := reflect.ValueOf(i)
-	if v.Kind() != reflect.Ptr {
-		panic(v)
-	}
-	y := `{}`
-	err := yaml.Unmarshal([]byte(y), v.Interface())
-	if err != nil {
-		panic(err)
-	}
-}
-
 type ConnectEnum struct {
 	Ret interface{}
 }
@@ -696,8 +683,16 @@ func ParseConfigBytes(bytes []byte) (*Config, error) {
 	if err := yaml.UnmarshalStrict(bytes, &c); err != nil {
 		return nil, err
 	}
+	if c != nil {
+		return c, nil
+	}
+	// There was no yaml document in the file, deserialize from default.
+	// => See TestFromdefaultsEmptyDoc in yaml-config package.
+	if err := yaml.UnmarshalStrict([]byte("{}"), &c); err != nil {
+		return nil, err
+	}
 	if c == nil {
-		return nil, fmt.Errorf("config is empty or only consists of comments")
+		panic("the fallback to deserialize from `{}` should work")
 	}
 	return c, nil
 }
diff --git a/config/config_minimal_test.go b/config/config_minimal_test.go
index 74747bf..ef87d38 100644
--- a/config/config_minimal_test.go
+++ b/config/config_minimal_test.go
@@ -2,16 +2,8 @@ package config
 
 import (
 	"testing"
-
-	"github.com/stretchr/testify/assert"
 )
 
-func TestConfigEmptyFails(t *testing.T) {
-	conf, err := testConfig(t, "\n")
-	assert.Nil(t, conf)
-	assert.Error(t, err)
-}
-
 func TestJobsOnlyWorks(t *testing.T) {
 	testValidConfig(t, `
 jobs:
@@ -34,7 +26,7 @@ jobs:
     keep_sender:
     - type: not_replicated
     keep_receiver:
-    - type: last_n 
+    - type: last_n
       count: 1
 `)
 }
diff --git a/config/config_test.go b/config/config_test.go
index 443f013..52387fb 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -22,6 +22,8 @@ func TestSampleConfigsAreParsedWithoutErrors(t *testing.T) {
 		t.Errorf("glob failed: %+v", err)
 	}
 
+	paths = append(paths, "../packaging/systemd-default-zrepl.yml")
+
 	for _, p := range paths {
 
 		if path.Ext(p) != ".yml" {
@@ -84,7 +86,7 @@ func trimSpaceEachLineAndPad(s, pad string) string {
 func TestTrimSpaceEachLineAndPad(t *testing.T) {
 	foo := `
 	foo
-	bar baz 
+	bar baz
 	`
 	assert.Equal(t, "  \n  foo\n  bar baz\n  \n", trimSpaceEachLineAndPad(foo, "  "))
 }
@@ -138,3 +140,18 @@ func TestCronSpec(t *testing.T) {
 	}
 
 }
+
+func TestEmptyConfig(t *testing.T) {
+	cases := []string{
+		"",
+		"\n",
+		"---",
+		"---\n",
+	}
+	for _, input := range cases {
+		config := testValidConfig(t, input)
+		require.NotNil(t, config)
+		require.NotNil(t, config.Global)
+		require.Empty(t, config.Jobs)
+	}
+}
diff --git a/config/samples/empty.yml b/config/samples/empty.yml
new file mode 100644
index 0000000..e69de29
diff --git a/packaging/systemd-default-zrepl.yml b/packaging/systemd-default-zrepl.yml
index d473aa0..9747090 100644
--- a/packaging/systemd-default-zrepl.yml
+++ b/packaging/systemd-default-zrepl.yml
@@ -5,9 +5,7 @@ global:
       format: human
       level: warn
 
-jobs:
-#  - name: foo
-#    type: bar
+jobs: []
 
 # see USR_SHARE_ZREPL/examples
 # or https://zrepl.github.io/configuration/overview.html