From 2a53b107c18e97d6240e2e94ac63fae18e0c4277 Mon Sep 17 00:00:00 2001
From: Fabian Reinartz <fab.reinartz@gmail.com>
Date: Fri, 17 Jul 2015 16:12:33 +0200
Subject: [PATCH 1/2] Fix missing defaults in empty configurations

---
 config/config.go      |  5 +++++
 config/config_test.go | 12 ++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/config/config.go b/config/config.go
index 888d5d628d..eddd440879 100644
--- a/config/config.go
+++ b/config/config.go
@@ -26,6 +26,11 @@ var (
 // Load parses the YAML input s into a Config.
 func Load(s string) (*Config, error) {
 	cfg := &Config{}
+	// If the entire config body is empty the UnmarshalYAML method is
+	// never called. We thus have to set the DefaultConfig at the entry
+	// point as well.
+	*cfg = DefaultConfig
+
 	err := yaml.Unmarshal([]byte(s), cfg)
 	if err != nil {
 		return nil, err
diff --git a/config/config_test.go b/config/config_test.go
index bba5fea1a3..d7aab0b489 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -249,3 +249,15 @@ func TestBadTargetGroup(t *testing.T) {
 		t.Errorf("Expected unmarshal error but got none.")
 	}
 }
+
+func TestEmptyConfig(t *testing.T) {
+	c, err := Load("")
+	if err != nil {
+		t.Fatalf("Unexpected error parsing empty config file: %s", err)
+	}
+	exp := DefaultConfig
+
+	if !reflect.DeepEqual(*c, exp) {
+		t.Fatalf("want %v, got %v", exp, c)
+	}
+}

From 187fe4e3d31f0ecaa0d7a386940acb3dcbf4e005 Mon Sep 17 00:00:00 2001
From: Fabian Reinartz <fab.reinartz@gmail.com>
Date: Fri, 17 Jul 2015 19:58:34 +0200
Subject: [PATCH 2/2] Fix missing defaults for empty global config blocks

---
 config/config.go      | 14 ++++++++++++++
 config/config_test.go | 13 +++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/config/config.go b/config/config.go
index eddd440879..46fbc9e757 100644
--- a/config/config.go
+++ b/config/config.go
@@ -147,6 +147,12 @@ func (c *Config) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	if err := unmarshal((*plain)(c)); err != nil {
 		return err
 	}
+	// If a global block was open but empty the default global config is overwritten.
+	// We have to restore it here.
+	if c.GlobalConfig.isZero() {
+		c.GlobalConfig = DefaultGlobalConfig
+	}
+
 	for _, rf := range c.RuleFiles {
 		if !patRulePath.MatchString(rf) {
 			return fmt.Errorf("invalid rule file path %q", rf)
@@ -196,6 +202,14 @@ func (c *GlobalConfig) UnmarshalYAML(unmarshal func(interface{}) error) error {
 	return checkOverflow(c.XXX, "global config")
 }
 
+// isZero returns true iff the global config is the zero value.
+func (c *GlobalConfig) isZero() bool {
+	return c.Labels == nil &&
+		c.ScrapeInterval == 0 &&
+		c.ScrapeTimeout == 0 &&
+		c.EvaluationInterval == 0
+}
+
 // ScrapeConfig configures a scraping unit for Prometheus.
 type ScrapeConfig struct {
 	// The job name to which the job label is set by default.
diff --git a/config/config_test.go b/config/config_test.go
index d7aab0b489..844aef8cdd 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -261,3 +261,16 @@ func TestEmptyConfig(t *testing.T) {
 		t.Fatalf("want %v, got %v", exp, c)
 	}
 }
+
+func TestEmptyGlobalBlock(t *testing.T) {
+	c, err := Load("global:\n")
+	if err != nil {
+		t.Fatalf("Unexpected error parsing empty config file: %s", err)
+	}
+	exp := DefaultConfig
+	exp.original = "global:\n"
+
+	if !reflect.DeepEqual(*c, exp) {
+		t.Fatalf("want %v, got %v", exp, c)
+	}
+}