TUN-7126: Add Management logger io.Writer

management/logger.go

@@ -0,0 +1,142 @@
+package management
+
+import (
+	"os"
+	"sync"
+	"time"
+
+	jsoniter "github.com/json-iterator/go"
+	"github.com/rs/zerolog"
+)
+
+var json = jsoniter.ConfigFastest
+
+const (
+	// Indicates how many log messages the listener will hold before dropping.
+	// Provides a throttling mechanism to drop latest messages if the sender
+	// can't keep up with the influx of log messages.
+	logWindow = 30
+)
+
+// ZeroLogEvent is the json structure that zerolog stores it's events as
+type ZeroLogEvent struct {
+	Time    string       `json:"time,omitempty"`
+	Level   LogLevel     `json:"level,omitempty"`
+	Type    LogEventType `json:"type,omitempty"`
+	Message string       `json:"message,omitempty"`
+}
+
+// Logger manages the number of management streaming log sessions
+type Logger struct {
+	sessions []*Session
+	mu       sync.RWMutex
+
+	// Unique logger that isn't a io.Writer of the list of zerolog writers. This helps prevent management log
+	// statements from creating infinite recursion to export messages to a session and allows basic debugging and
+	// error statements to be issued in the management code itself.
+	Log *zerolog.Logger
+}
+
+func NewLogger() *Logger {
+	log := zerolog.New(zerolog.ConsoleWriter{
+		Out:        os.Stdout,
+		TimeFormat: time.RFC3339,
+	}).With().Timestamp().Logger().Level(zerolog.DebugLevel)
+	return &Logger{
+		Log: &log,
+	}
+}
+
+type LoggerListener interface {
+	Listen() *Session
+	Close(*Session)
+}
+
+type Session struct {
+	// Buffered channel that holds the recent log events
+	listener chan *ZeroLogEvent
+	// Types of log events that this session will provide through the listener
+	filters []LogEventType
+}
+
+func newListener(size int) *Session {
+	return &Session{
+		listener: make(chan *ZeroLogEvent, size),
+		filters:  []LogEventType{},
+	}
+}
+
+// Listen creates a new Session that will append filtered log events as they are created.
+func (l *Logger) Listen() *Session {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	listener := newListener(logWindow)
+	l.sessions = append(l.sessions, listener)
+	return listener
+}
+
+// Close will remove a Session from the available sessions that were receiving log events.
+func (l *Logger) Close(session *Session) {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	index := -1
+	for i, v := range l.sessions {
+		if v == session {
+			index = i
+			break
+		}
+	}
+	if index == -1 {
+		// Not found
+		return
+	}
+	copy(l.sessions[index:], l.sessions[index+1:])
+	l.sessions = l.sessions[:len(l.sessions)-1]
+}
+
+// Write will write the log event to all sessions that have available capacity. For those that are full, the message
+// will be dropped.
+// This function is the interface that zerolog expects to call when a log event is to be written out.
+func (l *Logger) Write(p []byte) (int, error) {
+	l.mu.RLock()
+	defer l.mu.RUnlock()
+	// return early if no active sessions
+	if len(l.sessions) == 0 {
+		return len(p), nil
+	}
+	var event ZeroLogEvent
+	iter := json.BorrowIterator(p)
+	defer json.ReturnIterator(iter)
+	iter.ReadVal(&event)
+	if iter.Error != nil {
+		l.Log.Debug().Msg("unable to unmarshal log event")
+		return len(p), nil
+	}
+	for _, listener := range l.sessions {
+		// no filters means all types are allowed
+		if len(listener.filters) != 0 {
+			valid := false
+			// make sure listener is subscribed to this event type
+			for _, t := range listener.filters {
+				if t == event.Type {
+					valid = true
+					break
+				}
+			}
+			if !valid {
+				continue
+			}
+		}
+
+		select {
+		case listener.listener <- &event:
+		default:
+			// buffer is full, discard
+		}
+	}
+	return len(p), nil
+}
+
+func (l *Logger) WriteLevel(level zerolog.Level, p []byte) (n int, err error) {
+	return l.Write(p)
+}