Fix issue where default go logger is not discarded when either * or s…

…tdout is selected. (elastic#15708)

* Disable default logger when stdlog or the default all selector is not enabled.

* Fix issue where default go logger is not discarded when either * or stdout is selected. Fix elastic#10251.

* Change logic to always discard unless in debug and when all or stdlog is selected. Add more tests.

* Fix comments.

* Add changelog entry.

CHANGELOG.next.asciidoc

@@ -46,6 +46,8 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...master[Check the HEAD d
 - Do not load dashboards where not available. {pull}15802[15802]
 - Fix issue where TLS settings would be ignored when a forward proxy was in use. {pull}15516{15516}
 - Update replicaset group to apps/v1 {pull}15854[15802]
+- Fix issue where default go logger is not discarded when either * or stdout is selected. {issue}10251[10251] {pull}15708[15708]
+
 
 *Auditbeat*
 

libbeat/logp/core.go

@@ -37,7 +37,8 @@ import (
 )
 
 var (
-	_log unsafe.Pointer // Pointer to a coreLogger. Access via atomic.LoadPointer.
+	_log          unsafe.Pointer // Pointer to a coreLogger. Access via atomic.LoadPointer.
+	_defaultGoLog = golog.Writer()
 )
 
 func init() {
@@ -86,6 +87,10 @@ func Configure(cfg Config) error {
 		return errors.Wrap(err, "failed to build log output")
 	}
 
+	// Default logger is always discard, debug level below will
+	// possibly re-enable it.
+	golog.SetOutput(ioutil.Discard)
+
 	// Enabled selectors when debug is enabled.
 	selectors := make(map[string]struct{}, len(cfg.Selectors))
 	if cfg.Level.Enabled(DebugLevel) && len(cfg.Selectors) > 0 {
@@ -98,10 +103,12 @@ func Configure(cfg Config) error {
 			selectors["*"] = struct{}{}
 		}
 
-		if _, enabled := selectors["stdlog"]; !enabled {
-			// Disable standard logging by default (this is sometimes used by
-			// libraries and we don't want their spam).
-			golog.SetOutput(ioutil.Discard)
+		// Re-enable the default go logger output when either stdlog
+		// or all selector is enabled.
+		_, stdlogEnabled := selectors["stdlog"]
+		_, allEnabled := selectors["*"]
+		if stdlogEnabled || allEnabled {
+			golog.SetOutput(_defaultGoLog)
 		}
 
 		sink = selectiveWrapper(sink, selectors)

libbeat/logp/core_test.go

@@ -18,6 +18,8 @@
 package logp
 
 import (
+	"io/ioutil"
+	golog "log"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -116,3 +118,31 @@ func TestL(t *testing.T) {
 		assert.Equal(t, "warning 1", log.Message)
 	}
 }
+
+func TestDebugAllStdoutEnablesDefaultGoLogger(t *testing.T) {
+	DevelopmentSetup(WithSelectors("*"))
+	assert.Equal(t, _defaultGoLog, golog.Writer())
+
+	DevelopmentSetup(WithSelectors("stdlog"))
+	assert.Equal(t, _defaultGoLog, golog.Writer())
+
+	DevelopmentSetup(WithSelectors("*", "stdlog"))
+	assert.Equal(t, _defaultGoLog, golog.Writer())
+
+	DevelopmentSetup(WithSelectors("other"))
+	assert.Equal(t, ioutil.Discard, golog.Writer())
+}
+
+func TestNotDebugAllStdoutDisablesDefaultGoLogger(t *testing.T) {
+	DevelopmentSetup(WithSelectors("*"), WithLevel(InfoLevel))
+	assert.Equal(t, ioutil.Discard, golog.Writer())
+
+	DevelopmentSetup(WithSelectors("stdlog"), WithLevel(InfoLevel))
+	assert.Equal(t, ioutil.Discard, golog.Writer())
+
+	DevelopmentSetup(WithSelectors("*", "stdlog"), WithLevel(InfoLevel))
+	assert.Equal(t, ioutil.Discard, golog.Writer())
+
+	DevelopmentSetup(WithSelectors("other"), WithLevel(InfoLevel))
+	assert.Equal(t, ioutil.Discard, golog.Writer())
+}