consul/logging/logger.go

package logging

import (
	"fmt"
	"io"
	"path/filepath"
	"time"

	"github.com/hashicorp/go-hclog"
	gsyslog "github.com/hashicorp/go-syslog"
)

// Config is used to set up logging.
type Config struct {
	// LogLevel is the minimum level to be logged.
	LogLevel string

	// LogJSON controls outputing logs in a JSON format.
	LogJSON bool

	// Name is the name the returned logger will use to prefix log lines.
	Name string

	// EnableSyslog controls forwarding to syslog.
	EnableSyslog bool

	// SyslogFacility is the destination for syslog forwarding.
	SyslogFacility string

	// LogFilePath is the path to write the logs to the user specified file.
	LogFilePath string

	// LogRotateDuration is the user specified time to rotate logs
	LogRotateDuration time.Duration

	// LogRotateBytes is the user specified byte limit to rotate logs
	LogRotateBytes int

	// LogRotateMaxFiles is the maximum number of past archived log files to keep
	LogRotateMaxFiles int
}

// defaultRotateDuration is the default time taken by the agent to rotate logs
const defaultRotateDuration = 24 * time.Hour

type LogSetupErrorFn func(string)

// noErrorWriter is a wrapper to suppress errors when writing to w.
type noErrorWriter struct {
	w io.Writer
}

func (w noErrorWriter) Write(p []byte) (n int, err error) {
	_, _ = w.w.Write(p)
	// We purposely return n == len(p) as if write was successful
	return len(p), nil
}

// Setup logging from Config, and return an hclog Logger.
//
// Logs may be written to out, and optionally to syslog, and a file.
func Setup(config Config, out io.Writer) (hclog.InterceptLogger, error) {
	if !ValidateLogLevel(config.LogLevel) {
		return nil, fmt.Errorf("Invalid log level: %s. Valid log levels are: %v",
			config.LogLevel,
			allowedLogLevels)
	}

	// If out is os.Stdout and Consul is being run as a Windows Service, writes will
	// fail silently, which may inadvertently prevent writes to other writers.
	// noErrorWriter is used as a wrapper to suppress any errors when writing to out.
	writers := []io.Writer{noErrorWriter{w: out}}

	if config.EnableSyslog {
		retries := 12
		delay := 5 * time.Second
		for i := 0; i <= retries; i++ {
			syslog, err := gsyslog.NewLogger(gsyslog.LOG_NOTICE, config.SyslogFacility, "consul")
			if err == nil {
				writers = append(writers, syslog)
				break
			}

			if i == retries {
				timeout := time.Duration(retries) * delay
				return nil, fmt.Errorf("Syslog setup did not succeed within timeout (%s).", timeout.String())
			}

			time.Sleep(delay)
		}
	}

	// Create a file logger if the user has specified the path to the log file
	if config.LogFilePath != "" {
		dir, fileName := filepath.Split(config.LogFilePath)
		if fileName == "" {
			fileName = "consul.log"
		}
		if config.LogRotateDuration == 0 {
			config.LogRotateDuration = defaultRotateDuration
		}
		logFile := &LogFile{
			fileName: fileName,
			logPath:  dir,
			duration: config.LogRotateDuration,
			MaxBytes: config.LogRotateBytes,
			MaxFiles: config.LogRotateMaxFiles,
		}
		if err := logFile.pruneFiles(); err != nil {
			return nil, fmt.Errorf("Failed to prune log files: %w", err)
		}
		if err := logFile.openNew(); err != nil {
			return nil, fmt.Errorf("Failed to setup logging: %w", err)
		}
		writers = append(writers, logFile)
	}

	logger := hclog.NewInterceptLogger(&hclog.LoggerOptions{
		Level:      LevelFromString(config.LogLevel),
		Name:       config.Name,
		Output:     io.MultiWriter(writers...),
		JSONFormat: config.LogJSON,
	})
	return logger, nil
}