bugfix: Default OTLP config not respected when `otlp:` block is unset (#16693)

Co-authored-by: Jan-Otto Kröpke <mail@jkroepke.de>

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changelog
 
+## 3.4.2 / 2025-06-04
+
+* [BUGFIX] OTLP receiver: Fix default configuration not being respected if the `otlp:` block is unset in the config file. #16693
+
 ## 3.4.1 / 2025-05-31
 
 * [BUGFIX] Parser: Add reproducer for a dangling-reference issue in parsers. #16633

config/config.go

@@ -157,6 +157,7 @@ var (
 	DefaultConfig = Config{
 		GlobalConfig: DefaultGlobalConfig,
 		Runtime:      DefaultRuntimeConfig,
+		OTLPConfig:   DefaultOTLPConfig,
 	}
 
 	// DefaultGlobalConfig is the default global configuration.

config/config_default_test.go

@@ -22,6 +22,7 @@ var ruleFilesExpectedConf = &Config{
 
 	GlobalConfig: DefaultGlobalConfig,
 	Runtime:      DefaultRuntimeConfig,
+	OTLPConfig:   DefaultOTLPConfig,
 	RuleFiles: []string{
 		"testdata/first.rules",
 		"testdata/rules/second.rules",

config/config_test.go

@@ -1775,6 +1775,26 @@ func TestOTLPAllowUTF8(t *testing.T) {
 			verify(t, err)
 		})
 	})
+
+	t.Run("good config - missing otlp config uses default", func(t *testing.T) {
+		fpath := filepath.Join("testdata", "otlp_empty.yml")
+		verify := func(t *testing.T, conf *Config, err error) {
+			t.Helper()
+			require.NoError(t, err)
+			require.Equal(t, UnderscoreEscapingWithSuffixes, conf.OTLPConfig.TranslationStrategy)
+		}
+
+		t.Run("LoadFile", func(t *testing.T) {
+			conf, err := LoadFile(fpath, false, promslog.NewNopLogger())
+			verify(t, conf, err)
+		})
+		t.Run("Load", func(t *testing.T) {
+			content, err := os.ReadFile(fpath)
+			require.NoError(t, err)
+			conf, err := Load(string(content), promslog.NewNopLogger())
+			verify(t, conf, err)
+		})
+	})
 }
 
 func TestLoadConfig(t *testing.T) {

config/testdata/otlp_empty.yml

@@ -0,0 +1 @@
+global: