Move cncd/{logging,pubsub,queue}/ to server/{logging,pubsub,queue}/ (#346)

* Move cncd/{logging,pubsub,queue}/ to server/{logging,pubsub,queue}/

* Update REAMDEs and include history

Co-authored-by: Anbraten <anton@ju60.de>

Co-authored-by: Anbraten <anton@ju60.de>

server/logging/log.go

@@ -0,0 +1,143 @@
+package logging
+
+import (
+	"context"
+	"io"
+	"sync"
+)
+
+// TODO (bradrydzewski) writing to subscribers is currently a blocking
+// operation and does not protect against slow clients from locking
+// the stream. This should be resolved.
+
+// TODO (bradrydzewski) implement a mux.Info to fetch information and
+// statistics for the multiplexier. Streams, subscribers, etc
+// mux.Info()
+
+// TODO (bradrydzewski) refactor code to place publisher and subscriber
+// operations in separate files with more encapsulated logic.
+// sub.push()
+// sub.join()
+// sub.start()... event loop
+
+type subscriber struct {
+	handler Handler
+}
+
+type stream struct {
+	sync.Mutex
+
+	path string
+	hist []*Entry
+	subs map[*subscriber]struct{}
+	done chan struct{}
+	wait sync.WaitGroup
+}
+
+type log struct {
+	sync.Mutex
+
+	streams map[string]*stream
+}
+
+// New returns a new logger.
+func New() Log {
+	return &log{
+		streams: map[string]*stream{},
+	}
+}
+
+func (l *log) Open(c context.Context, path string) error {
+	l.Lock()
+	_, ok := l.streams[path]
+	if !ok {
+		l.streams[path] = &stream{
+			path: path,
+			subs: make(map[*subscriber]struct{}),
+			done: make(chan struct{}),
+		}
+	}
+	l.Unlock()
+	return nil
+}
+
+func (l *log) Write(c context.Context, path string, entry *Entry) error {
+	l.Lock()
+	s, ok := l.streams[path]
+	l.Unlock()
+	if !ok {
+		return ErrNotFound
+	}
+	s.Lock()
+	s.hist = append(s.hist, entry)
+	for sub := range s.subs {
+		go sub.handler(entry)
+	}
+	s.Unlock()
+	return nil
+}
+
+func (l *log) Tail(c context.Context, path string, handler Handler) error {
+	l.Lock()
+	s, ok := l.streams[path]
+	l.Unlock()
+	if !ok {
+		return ErrNotFound
+	}
+
+	sub := &subscriber{
+		handler: handler,
+	}
+	s.Lock()
+	if len(s.hist) != 0 {
+		sub.handler(s.hist...)
+	}
+	s.subs[sub] = struct{}{}
+	s.Unlock()
+
+	select {
+	case <-c.Done():
+	case <-s.done:
+	}
+
+	s.Lock()
+	delete(s.subs, sub)
+	s.Unlock()
+	return nil
+}
+
+func (l *log) Close(c context.Context, path string) error {
+	l.Lock()
+	s, ok := l.streams[path]
+	l.Unlock()
+	if !ok {
+		return ErrNotFound
+	}
+
+	s.Lock()
+	close(s.done)
+	s.Unlock()
+
+	l.Lock()
+	delete(l.streams, path)
+	l.Unlock()
+	return nil
+}
+
+func (l *log) Snapshot(c context.Context, path string, w io.Writer) error {
+	l.Lock()
+	s, ok := l.streams[path]
+	l.Unlock()
+	if !ok {
+		return ErrNotFound
+	}
+	s.Lock()
+	for _, entry := range s.hist {
+		w.Write(entry.Data)
+		w.Write(cr)
+	}
+	s.Unlock()
+	return nil
+}
+
+var cr = []byte{'\n'}