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.

vendor/github.com/mattermost/logr/levelcache.go

@@ -0,0 +1,98 @@
+package logr
+
+import (
+	"fmt"
+	"sync"
+)
+
+// LevelStatus represents whether a level is enabled and
+// requires a stack trace.
+type LevelStatus struct {
+	Enabled    bool
+	Stacktrace bool
+	empty      bool
+}
+
+type levelCache interface {
+	setup()
+	get(id LevelID) (LevelStatus, bool)
+	put(id LevelID, status LevelStatus) error
+	clear()
+}
+
+// syncMapLevelCache uses sync.Map which may better handle large concurrency
+// scenarios.
+type syncMapLevelCache struct {
+	m sync.Map
+}
+
+func (c *syncMapLevelCache) setup() {
+	c.clear()
+}
+
+func (c *syncMapLevelCache) get(id LevelID) (LevelStatus, bool) {
+	if id > MaxLevelID {
+		return LevelStatus{}, false
+	}
+	s, _ := c.m.Load(id)
+	status := s.(LevelStatus)
+	return status, !status.empty
+}
+
+func (c *syncMapLevelCache) put(id LevelID, status LevelStatus) error {
+	if id > MaxLevelID {
+		return fmt.Errorf("level id cannot exceed MaxLevelID (%d)", MaxLevelID)
+	}
+	c.m.Store(id, status)
+	return nil
+}
+
+func (c *syncMapLevelCache) clear() {
+	var i LevelID
+	for i = 0; i < MaxLevelID; i++ {
+		c.m.Store(i, LevelStatus{empty: true})
+	}
+}
+
+// arrayLevelCache using array and a mutex.
+type arrayLevelCache struct {
+	arr [MaxLevelID + 1]LevelStatus
+	mux sync.RWMutex
+}
+
+func (c *arrayLevelCache) setup() {
+	c.clear()
+}
+
+//var dummy = LevelStatus{}
+
+func (c *arrayLevelCache) get(id LevelID) (LevelStatus, bool) {
+	if id > MaxLevelID {
+		return LevelStatus{}, false
+	}
+	c.mux.RLock()
+	status := c.arr[id]
+	ok := !status.empty
+	c.mux.RUnlock()
+	return status, ok
+}
+
+func (c *arrayLevelCache) put(id LevelID, status LevelStatus) error {
+	if id > MaxLevelID {
+		return fmt.Errorf("level id cannot exceed MaxLevelID (%d)", MaxLevelID)
+	}
+	c.mux.Lock()
+	defer c.mux.Unlock()
+
+	c.arr[id] = status
+	return nil
+}
+
+func (c *arrayLevelCache) clear() {
+	c.mux.Lock()
+	defer c.mux.Unlock()
+
+	for i := range c.arr {
+		c.arr[i] = LevelStatus{empty: true}
+	}
+}