[logp] Add typed loggers allowing log entries to go to a different output (#171)

This commit introduces a typedLogger that allows a log entry to be
directed to a different output when a configurable key/value are
present in the log fields.

This enables Beats and Elastic-Agent to log event data to a separate
log file.

Author: belimawr

logp/config.go

@@ -88,6 +88,30 @@ func DefaultConfig(environment Environment) Config {
 	}
 }
 
+// DefaultEventConfig returns the default config options for the event logger in
+// a given environment the Beat is supposed to be run within.
+func DefaultEventConfig(environment Environment) Config {
+	return Config{
+		Level:    defaultLevel,
+		ToFiles:  true,
+		ToStderr: false,
+		Files: FileConfig{
+			MaxSize:         5 * 1024 * 1024, // 5Mb
+			MaxBackups:      2,
+			Permissions:     0600,
+			Interval:        0,
+			RotateOnStartup: false,
+			RedirectStderr:  false,
+			Name:            "event-data",
+		},
+		Metrics: MetricsConfig{
+			Enabled: false,
+		},
+		environment: environment,
+		addCaller:   true,
+	}
+}
+
 // LogFilename returns the base filename to which logs will be written for
 // the "files" log output. If another log output is used, or `logging.files.name`
 // is unspecified, then the beat name will be returned.

logp/configure/logging.go

@@ -45,6 +45,10 @@ func init() {
 	flag.Var((*environmentVar)(&environment), "environment", "set environment being ran in")
 }
 
+func GetEnvironment() logp.Environment {
+	return environment
+}
+
 // Logging builds a logp.Config based on the given common.Config and the specified
 // CLI flags.
 func Logging(beatName string, cfg *config.C) error {
@@ -75,6 +79,39 @@ func LoggingWithOutputs(beatName string, cfg *config.C, outputs ...zapcore.Core)
 	return logp.ConfigureWithOutputs(config, outputs...)
 }
 
+// LoggingWithTypedOutputs applies some defaults then calls ConfigureWithTypedOutputs
+func LoggingWithTypedOutputs(beatName string, cfg, typedCfg *config.C, logKey, kind string, outputs ...zapcore.Core) error {
+	config := logp.DefaultConfig(environment)
+	config.Beat = beatName
+	if cfg != nil {
+		if err := cfg.Unpack(&config); err != nil {
+			return err
+		}
+	}
+
+	applyFlags(&config)
+
+	typedLogpConfig := logp.DefaultEventConfig(environment)
+	defaultName := typedLogpConfig.Files.Name
+	typedLogpConfig.Beat = beatName
+	if typedCfg != nil {
+		if err := typedCfg.Unpack(&typedLogpConfig); err != nil {
+			return fmt.Errorf("cannot unpack typed output config: %w", err)
+		}
+	}
+
+	// Make sure we're always running on the same log level
+	typedLogpConfig.Level = config.Level
+	typedLogpConfig.Selectors = config.Selectors
+
+	// If the name has not been configured, make it {beatName}-events-data
+	if typedLogpConfig.Files.Name == defaultName {
+		typedLogpConfig.Files.Name = beatName + "-events-data"
+	}
+
+	return logp.ConfigureWithTypedOutput(config, typedLogpConfig, logKey, kind, outputs...)
+}
+
 func applyFlags(cfg *logp.Config) {
 	if toStderr {
 		cfg.ToStderr = true

logp/core.go

@@ -21,7 +21,7 @@ import (
 	"errors"
 	"flag"
 	"fmt"
-	"io/ioutil"
+	"io"
 	golog "log"
 	"os"
 	"path/filepath"
@@ -68,36 +68,33 @@ func Configure(cfg Config) error {
 	return ConfigureWithOutputs(cfg)
 }
 
-// ConfigureWithOutputs XXX: is used by elastic-agent only (See file: x-pack/elastic-agent/pkg/core/logger/logger.go).
-// The agent requires that the output specified in the config object is configured and merged with the
-// logging outputs given.
-func ConfigureWithOutputs(cfg Config, outputs ...zapcore.Core) error {
+func createSink(defaultLoggerCfg Config, outputs ...zapcore.Core) (zapcore.Core, zap.AtomicLevel, *observer.ObservedLogs, map[string]struct{}, error) {
 	var (
 		sink         zapcore.Core
 		observedLogs *observer.ObservedLogs
 		err          error
 		level        zap.AtomicLevel
 	)
 
-	level = zap.NewAtomicLevelAt(cfg.Level.ZapLevel())
+	level = zap.NewAtomicLevelAt(defaultLoggerCfg.Level.ZapLevel())
 	// Build a single output (stderr has priority if more than one are enabled).
-	if cfg.toObserver {
+	if defaultLoggerCfg.toObserver {
 		sink, observedLogs = observer.New(level)
 	} else {
-		sink, err = createLogOutput(cfg, level)
+		sink, err = createLogOutput(defaultLoggerCfg, level)
 	}
 	if err != nil {
-		return fmt.Errorf("failed to build log output: %w", err)
+		return nil, level, nil, nil, fmt.Errorf("failed to build log output: %w", err)
 	}
 
 	// Default logger is always discard, debug level below will
 	// possibly re-enable it.
-	golog.SetOutput(ioutil.Discard)
+	golog.SetOutput(io.Discard)
 
 	// Enabled selectors when debug is enabled.
-	selectors := make(map[string]struct{}, len(cfg.Selectors))
-	if cfg.Level.Enabled(DebugLevel) && len(cfg.Selectors) > 0 {
-		for _, sel := range cfg.Selectors {
+	selectors := make(map[string]struct{}, len(defaultLoggerCfg.Selectors))
+	if defaultLoggerCfg.Level.Enabled(DebugLevel) && len(defaultLoggerCfg.Selectors) > 0 {
+		for _, sel := range defaultLoggerCfg.Selectors {
 			selectors[strings.TrimSpace(sel)] = struct{}{}
 		}
 
@@ -118,7 +115,73 @@ func ConfigureWithOutputs(cfg Config, outputs ...zapcore.Core) error {
 	}
 
 	sink = newMultiCore(append(outputs, sink)...)
-	root := zap.New(sink, makeOptions(cfg)...)
+
+	return sink, level, observedLogs, selectors, err
+}
+
+// ConfigureWithOutputs configures the global logger to use an output created
+// from `defaultLoggerCfg` and all the outputs passed by `outputs`.
+// This function needs to be exported because it's used by `logp/configure`
+func ConfigureWithOutputs(defaultLoggerCfg Config, outputs ...zapcore.Core) error {
+	sink, level, observedLogs, selectors, err := createSink(defaultLoggerCfg, outputs...)
+	if err != nil {
+		return err
+	}
+	root := zap.New(sink, makeOptions(defaultLoggerCfg)...)
+	storeLogger(&coreLogger{
+		selectors:    selectors,
+		rootLogger:   root,
+		globalLogger: root.WithOptions(zap.AddCallerSkip(1)),
+		logger:       newLogger(root, ""),
+		level:        level,
+		observedLogs: observedLogs,
+	})
+	return nil
+}
+
+// ConfigureWithTypedOutput configures the global logger to use typed outputs.
+//
+// If a log entry matches the defined key/value, this entry is logged using the
+// core generated from `typedLoggerCfg`, otherwise it will be logged by all
+// cores in `outputs` and the one generated from `defaultLoggerCfg`.
+// Arguments:
+//   - `defaultLoggerCfg` is used to create a new core that will be the default
+//     output from the logger
+//   - `typedLoggerCfg` is used to create a new output that will only be used
+//     when the log entry matches `entry[logKey] = kind`
+//   - `key` is the key the typed logger will look at
+//   - `value` is the value compared against the `logKey` entry
+//   - `outputs` is a list of cores that will be added together with the core
+//     generated by `defaultLoggerCfg` as the default output for the loggger.
+//
+// If `defaultLoggerCfg.toObserver` is true, then `typedLoggerCfg` is ignored
+// and a single sink is used so all logs can be observed.
+func ConfigureWithTypedOutput(defaultLoggerCfg, typedLoggerCfg Config, key, value string, outputs ...zapcore.Core) error {
+	sink, level, observedLogs, selectors, err := createSink(defaultLoggerCfg, outputs...)
+	if err != nil {
+		return err
+	}
+
+	var typedCore zapcore.Core
+	if defaultLoggerCfg.toObserver {
+		typedCore = sink
+	} else {
+		typedCore, err = createLogOutput(typedLoggerCfg, level)
+	}
+	if err != nil {
+		return fmt.Errorf("could not create typed logger output: %w", err)
+	}
+
+	sink = &typedLoggerCore{
+		defaultCore: sink,
+		typedCore:   typedCore,
+		key:         key,
+		value:       value,
+	}
+
+	sink = selectiveWrapper(sink, selectors)
+
+	root := zap.New(sink, makeOptions(defaultLoggerCfg)...)
 	storeLogger(&coreLogger{
 		selectors:    selectors,
 		rootLogger:   root,
@@ -215,7 +278,7 @@ func makeStderrOutput(cfg Config, enab zapcore.LevelEnabler) (zapcore.Core, erro
 }
 
 func makeDiscardOutput(cfg Config, enab zapcore.LevelEnabler) (zapcore.Core, error) {
-	discard := zapcore.AddSync(ioutil.Discard)
+	discard := zapcore.AddSync(io.Discard)
 	return newCore(buildEncoder(cfg), discard, enab), nil
 }