agent: remove unused log filter and unrequired library. (#24873)

The Nomad agent used a log filter to ensure logs were written at
the expected level. Since the use of hclog this is not required,
as hclog acts as the gate keeper and filter for logging. All log
writers accept messages from hclog which has already done the
filtering.

command/agent/command.go

@@ -28,7 +28,6 @@ import (
 	discover "github.com/hashicorp/go-discover"
 	hclog "github.com/hashicorp/go-hclog"
 	gsyslog "github.com/hashicorp/go-syslog"
-	"github.com/hashicorp/logutils"
 	"github.com/hashicorp/nomad/helper"
 	flaghelper "github.com/hashicorp/nomad/helper/flags"
 	gatedwriter "github.com/hashicorp/nomad/helper/gated-writer"
@@ -55,8 +54,6 @@ type Command struct {
 	args           []string
 	agent          *Agent
 	httpServers    []*HTTPServer
-	logFilter      *logutils.LevelFilter
-	logOutput      io.Writer
 	retryJoinErrCh chan struct{}
 }
 
@@ -552,28 +549,31 @@ func (c *Command) IsValidConfig(config, cmdConfig *Config) bool {
 	return true
 }
 
-// SetupLoggers is used to set up the logGate, and our logOutput
-func SetupLoggers(ui cli.Ui, config *Config) (*logutils.LevelFilter, *gatedwriter.Writer, io.Writer) {
-	// Setup logging. First create the gated log writer, which will
-	// store logs until we're ready to show them. Then create the level
-	// filter, filtering logs of the specified level.
+// setupLoggers is used to set up the logGate and our logOutput.
+func setupLoggers(ui cli.Ui, config *Config) (*gatedwriter.Writer, io.Writer) {
+
+	// Pull the log level from the configuration, ensure it is titled and then
+	// perform validation. Do this before the gated writer, as this can
+	// generate an error, whereas the writer does not.
+	logLevel := strings.ToUpper(config.LogLevel)
+
+	if !isLogLevelValid(logLevel) {
+		ui.Error(fmt.Sprintf(
+			"Invalid log level: %s. Valid log levels are: %v",
+			logLevel, validLogLevels.Slice()))
+		return nil, nil
+	}
+
+	// Create a gated log writer, which will store logs until we're ready to
+	// output them.
 	logGate := &gatedwriter.Writer{
 		Writer: &cli.UiWriter{Ui: ui},
 	}
 
-	logFilter := LevelFilter()
-	logFilter.MinLevel = logutils.LogLevel(strings.ToUpper(config.LogLevel))
-	logFilter.Writer = logGate
-	if !ValidateLevelFilter(logFilter.MinLevel, logFilter) {
-		ui.Error(fmt.Sprintf(
-			"Invalid log level: %s. Valid log levels are: %v",
-			logFilter.MinLevel, logFilter.Levels))
-		return nil, nil, nil
-	}
+	// Initialize our array of log writers with the gated writer. Additional
+	// log writers will be appended if/when configured.
+	writers := []io.Writer{logGate}
 
-	// Create a log writer, and wrap a logOutput around it
-	writers := []io.Writer{logFilter}
-	logLevel := strings.ToUpper(config.LogLevel)
 	if logLevel == "OFF" {
 		config.EnableSyslog = false
 	}
@@ -583,7 +583,7 @@ func SetupLoggers(ui cli.Ui, config *Config) (*logutils.LevelFilter, *gatedwrite
 		l, err := gsyslog.NewLogger(getSysLogPriority(logLevel), config.SyslogFacility, "nomad")
 		if err != nil {
 			ui.Error(fmt.Sprintf("Syslog setup failed: %v", err))
-			return nil, nil, nil
+			return nil, nil
 		}
 		writers = append(writers, newSyslogWriter(l, config.LogJson))
 	}
@@ -603,7 +603,7 @@ func SetupLoggers(ui cli.Ui, config *Config) (*logutils.LevelFilter, *gatedwrite
 			duration, err := time.ParseDuration(config.LogRotateDuration)
 			if err != nil {
 				ui.Error(fmt.Sprintf("Failed to parse log rotation duration: %v", err))
-				return nil, nil, nil
+				return nil, nil
 			}
 			logRotateDuration = duration
 		} else {
@@ -612,19 +612,18 @@ func SetupLoggers(ui cli.Ui, config *Config) (*logutils.LevelFilter, *gatedwrite
 		}
 
 		logFile := &logFile{
-			logFilter: logFilter,
-			fileName:  fileName,
-			logPath:   dir,
-			duration:  logRotateDuration,
-			MaxBytes:  config.LogRotateBytes,
-			MaxFiles:  config.LogRotateMaxFiles,
+			fileName: fileName,
+			logPath:  dir,
+			duration: logRotateDuration,
+			MaxBytes: config.LogRotateBytes,
+			MaxFiles: config.LogRotateMaxFiles,
 		}
 
 		writers = append(writers, logFile)
 	}
 
 	logOutput := io.MultiWriter(writers...)
-	return logFilter, logGate, logOutput
+	return logGate, logOutput
 }
 
 // setupAgent is used to start the agent and various interfaces
@@ -801,10 +800,8 @@ func (c *Command) Run(args []string) int {
 		}
 	}
 
-	// Setup the log outputs
-	logFilter, logGate, logOutput := SetupLoggers(c.Ui, config)
-	c.logFilter = logFilter
-	c.logOutput = logOutput
+	// Set up the log outputs.
+	logGate, logOutput := setupLoggers(c.Ui, config)
 	if logGate == nil {
 		return 1
 	}
@@ -1116,13 +1113,12 @@ func (c *Command) handleReload() {
 	}
 
 	// Change the log level
-	minLevel := logutils.LogLevel(strings.ToUpper(newConf.LogLevel))
-	if ValidateLevelFilter(minLevel, c.logFilter) {
-		c.logFilter.SetMinLevel(minLevel)
-	} else {
+	minLevel := strings.ToUpper(newConf.LogLevel)
+
+	if !isLogLevelValid(minLevel) {
 		c.Ui.Error(fmt.Sprintf(
 			"Invalid log level: %s. Valid log levels are: %v",
-			minLevel, c.logFilter.Levels))
+			minLevel, validLogLevels.Slice()))
 
 		// Keep the current log level
 		newConf.LogLevel = c.agent.GetConfig().LogLevel