MM-25731 Advanced Logging (#14888)

Adds Advanced Logging to server. Advanced Logging is an optional logging capability that allows customers to send log records to any number of destinations.

Supported destinations:
- file
- syslog (with out without TLS)
- raw TCP socket (with out without TLS)

Allows developers to specify discrete log levels as well as the standard trace, debug, info, ... panic. Existing code and logging API usage is unchanged.

Log records are emitted asynchronously to reduce latency to the caller. Supports hot-reloading of logger config, including adding removing targets.

Advanced Logging is configured within config.json via "LogSettings.AdvancedLoggingConfig" which can contain a filespec to another config file, a database DSN, or JSON.

mlog/default.go

@@ -4,9 +4,13 @@
 package mlog
 
 import (
+	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"os"
+
+	"github.com/mattermost/logr"
 )
 
 // defaultLog manually encodes the log to STDERR, providing a basic, default logging implementation
@@ -49,3 +53,31 @@ func defaultCriticalLog(msg string, fields ...Field) {
 	// We map critical to error in zap, so be consistent.
 	defaultLog("error", msg, fields...)
 }
+
+func defaultCustomLog(lvl LogLevel, msg string, fields ...Field) {
+	// custom log levels are only output once log targets are configured.
+}
+
+func defaultCustomMultiLog(lvl []LogLevel, msg string, fields ...Field) {
+	// custom log levels are only output once log targets are configured.
+}
+
+func defaultFlush(ctx context.Context) error {
+	return nil
+}
+
+func defaultAdvancedConfig(cfg LogTargetCfg) error {
+	// mlog.ConfigAdvancedConfig should not be called until default
+	// logger is replaced with mlog.Logger instance.
+	return errors.New("cannot config advanced logging on default logger")
+}
+
+func defaultAdvancedShutdown(ctx context.Context) error {
+	return nil
+}
+
+func defaultAddTarget(target logr.Target) error {
+	// mlog.AddTarget should not be called until default
+	// logger is replaced with mlog.Logger instance.
+	return errors.New("cannot AddTarget on default logger")
+}