Capture the logs from stderr of custom plugins.

pkg/custompluginmonitor/plugin/plugin.go

@@ -19,6 +19,8 @@ package plugin
 import (
 	"context"
 	"fmt"
+	"io"
+	"io/ioutil"
 	"os/exec"
 	"strings"
 	"sync"
@@ -30,6 +32,10 @@ import (
 	"k8s.io/node-problem-detector/pkg/util/tomb"
 )
 
+// maxCustomPluginBufferBytes is the max bytes that a custom plugin is allowed to
+// send to stdout/stderr. Any bytes exceeding this value will be truncated.
+const	maxCustomPluginBufferBytes = 1024 * 4
+
 type Plugin struct {
 	config     cpmtypes.CustomPluginConfig
 	syncChan   chan struct{}
@@ -127,14 +133,50 @@ func (p *Plugin) run(rule cpmtypes.CustomRule) (exitStatus cpmtypes.Status, outp
 	defer cancel()
 
 	cmd := exec.CommandContext(ctx, rule.Path, rule.Args...)
-	stdout, err := cmd.Output()
+
+	stdoutPipe, err := cmd.StdoutPipe()
+	if err != nil {
+		glog.Errorf("Error creating stdout pipe for plugin %q: error - %v", rule.Path, err)
+		return cpmtypes.Unknown, "Error creating stdout pipe for plugin. Please check the error log"
+	}
+	stderrPipe, err := cmd.StderrPipe()
+	if err != nil {
+		glog.Errorf("Error creating stderr pipe for plugin %q: error - %v", rule.Path, err)
+		return cpmtypes.Unknown, "Error creating stderr pipe for plugin. Please check the error log"
+	}
+	stdoutReader := io.LimitReader(stdoutPipe, maxCustomPluginBufferBytes)
+	stderrReader := io.LimitReader(stderrPipe, maxCustomPluginBufferBytes)
+
+	if err := cmd.Start(); err != nil {
+		glog.Errorf("Error in starting plugin %q: error - %v", rule.Path, err)
+		return cpmtypes.Unknown, "Error in starting plugin. Please check the error log"
+	}
+
+	stdout, err := ioutil.ReadAll(stdoutReader)
+	if err != nil {
+		glog.Errorf("Error reading stdout for plugin %q: error - %v", rule.Path, err)
+		return cpmtypes.Unknown, "Error reading stdout for plugin. Please check the error log"
+	}
+
+	stderr, err := ioutil.ReadAll(stderrReader)
 	if err != nil {
+		glog.Errorf("Error reading stderr for plugin %q: error - %v", rule.Path, err)
+		return cpmtypes.Unknown, "Error reading stderr for plugin. Please check the error log"
+	}
+
+	if err := cmd.Wait(); err != nil {
 		if _, ok := err.(*exec.ExitError); !ok {
-			glog.Errorf("Error in running plugin %q: error - %v. output - %q", rule.Path, err, string(stdout))
-			return cpmtypes.Unknown, "Error in running plugin. Please check the error log"
+			glog.Errorf("Error in waiting for plugin %q: error - %v. output - %q", rule.Path, err, string(stdout))
+			return cpmtypes.Unknown, "Error in waiting for plugin. Please check the error log"
 		}
 	}
 
+	// log the stderr from the plugin
+	if len(stderr) != 0 {
+		glog.Infof("Start logs from plugin %q \n %s\n", rule.Path, string(stderr))
+		glog.Infof("End logs from plugin %q\n", rule.Path)
+	}
+
 	// trim suffix useless bytes
 	output = string(stdout)
 	output = strings.TrimSpace(output)