Merge pull request #1024 from mackerelio/log-plugin-bug

Write out error message when plugin seems have a bug

agent/agent.go

@@ -2,6 +2,7 @@ package agent
 
 import (
 	"context"
+	"errors"
 	"time"
 
 	"github.com/mackerelio/mackerel-agent/checks"
@@ -98,7 +99,11 @@ func (agent *Agent) CollectGraphDefsOfPlugins() []*mkr.GraphDefsParam {
 
 	for _, g := range agent.PluginGenerators {
 		p, err := g.PrepareGraphDefs()
-		if err != nil {
+
+		var faultError *metrics.PluginFaultError
+		if errors.As(err, &faultError) {
+			logger.Errorf("Failed to fetch meta information from plugin %v; seems that the plugin has a bug: %v", g, err)
+		} else if err != nil {
 			logger.Debugf("Failed to fetch meta information from plugin %v (non critical); seems that this plugin does not have meta information: %v", g, err)
 		}
 		if p != nil {

metrics/metrics.go

@@ -42,3 +42,18 @@ type PluginGenerator interface {
 	PrepareGraphDefs() ([]*mkr.GraphDefsParam, error)
 	CustomIdentifier() *string
 }
+
+// PluginFaultError may be returned by [PluginGenerator.PrepareGraphDefs].
+// This error indicates a bug in a plugin and should be logged for a user.
+// Note that [PluginGenerator.PrepareGraphDefs] can also return other error types.
+type PluginFaultError struct {
+	Err error
+}
+
+func (e *PluginFaultError) Error() string {
+	return e.Err.Error()
+}
+
+func (e *PluginFaultError) Unwrap() error {
+	return e.Err
+}

metrics/plugin.go

@@ -125,7 +125,7 @@ func (g *pluginGenerator) loadPluginMeta() error {
 	pluginMetaEnv := pluginConfigurationEnvName + "=1"
 	stdout, stderr, exitCode, err := g.Config.Command.RunWithEnv([]string{pluginMetaEnv})
 	if err != nil {
-		return fmt.Errorf("running %s failed: %s, exit=%d stderr=%q", g.Config.Command.CommandString(), err, exitCode, stderr)
+		return &PluginFaultError{fmt.Errorf("running %s failed: %s, exit=%d stderr=%q", g.Config.Command.CommandString(), err, exitCode, stderr)}
 	}
 
 	outBuffer := bufio.NewReader(strings.NewReader(stdout))
@@ -170,7 +170,7 @@ func (g *pluginGenerator) loadPluginMeta() error {
 	err = json.NewDecoder(outBuffer).Decode(conf)
 
 	if err != nil {
-		return fmt.Errorf("while reading plugin configuration: %s", err)
+		return &PluginFaultError{fmt.Errorf("while reading plugin configuration: %s", err)}
 	}
 
 	g.Meta = conf