From 77267fa60c7cd4dcf4ab737e6756429fc69ce3ec Mon Sep 17 00:00:00 2001
From: Eric Lippmann <eric.lippmann@icinga.com>
Date: Wed, 3 Mar 2021 21:10:04 +0100
Subject: [PATCH] Introducte type icingaredis.Heartbeat

---
 pkg/icingaredis/heartbeat.go | 138 +++++++++++++++++++++++++++++++++++
 1 file changed, 138 insertions(+)
 create mode 100644 pkg/icingaredis/heartbeat.go

diff --git a/pkg/icingaredis/heartbeat.go b/pkg/icingaredis/heartbeat.go
new file mode 100644
index 00000000..51285351
--- /dev/null
+++ b/pkg/icingaredis/heartbeat.go
@@ -0,0 +1,138 @@
+package icingaredis
+
+import (
+	"context"
+	"github.com/go-redis/redis/v8"
+	v1 "github.com/icinga/icingadb/pkg/icingaredis/v1"
+	"github.com/icinga/icingadb/pkg/utils"
+	"go.uber.org/zap"
+	"golang.org/x/sync/errgroup"
+	"sync"
+	"time"
+)
+
+var timeout = 60 * time.Second
+
+type Heartbeat struct {
+	ctx    context.Context
+	cancel context.CancelFunc
+	client *Client
+	logger *zap.SugaredLogger
+	active bool
+	beat   chan interface{}
+	lost   chan interface{}
+	done   chan interface{}
+	mu     *sync.Mutex
+	err    error
+}
+
+func NewHeartbeat(ctx context.Context, client *Client, logger *zap.SugaredLogger) *Heartbeat {
+	ctx, cancel := context.WithCancel(ctx)
+
+	heartbeat := &Heartbeat{
+		ctx:    ctx,
+		cancel: cancel,
+		client: client,
+		logger: logger,
+		beat:   make(chan interface{}),
+		lost:   make(chan interface{}),
+		done:   make(chan interface{}),
+		mu:     &sync.Mutex{},
+	}
+
+	go heartbeat.controller()
+
+	return heartbeat
+}
+
+// Close implements the io.Closer interface.
+func (h Heartbeat) Close() error {
+	// Cancel ctx.
+	h.cancel()
+	// Wait until the controller loop ended.
+	<-h.Done()
+	// And return an error, if any.
+	return h.Err()
+}
+
+func (h Heartbeat) Done() <-chan interface{} {
+	return h.done
+}
+
+func (h Heartbeat) Err() error {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+
+	return h.err
+}
+
+func (h Heartbeat) Beat() <-chan interface{} {
+	return h.beat
+}
+
+func (h Heartbeat) Lost() <-chan interface{} {
+	return h.lost
+}
+
+// controller loop.
+func (h Heartbeat) controller() {
+	messages := make(chan interface{})
+	defer close(messages)
+
+	g, ctx := errgroup.WithContext(h.ctx)
+
+	// Message producer loop
+	g.Go(func() error {
+		// We expect heartbeats every second but only read them every 3 seconds
+		throttle := time.Tick(time.Second * 3)
+		for {
+			streams, err := h.client.XRead(ctx, &redis.XReadArgs{
+				Streams: []string{"icinga:stats", "$"},
+				Block:   0, // TODO(el): Might make sense to use a non-blocking variant here
+			}).Result()
+			if err != nil {
+				return err
+			}
+
+			select {
+			case messages <- v1.StatsMessage(streams[0].Messages[0].Values):
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+
+			<-throttle
+		}
+	})
+
+	// State loop
+	g.Go(func() error {
+		for {
+			select {
+			case m := <-messages:
+				h.active = true // TODO(el): We might only want to set this once
+				h.beat <- m
+			case <-time.After(timeout):
+				if h.active {
+					h.lost <- struct{}{}
+					h.active = false
+				}
+			case <-ctx.Done():
+				return ctx.Err()
+			}
+		}
+	})
+
+	// Since the goroutines of the group actually run endlessly,
+	// we wait here forever, unless an error occurs.
+	if err := g.Wait(); err != nil && !utils.IsContextCanceled(err) {
+		// Do not propagate context-aborted errors here,
+		// as this is to be expected when Close was called.
+		h.setError(err)
+	}
+}
+
+func (h *Heartbeat) setError(err error) {
+	h.mu.Lock()
+	h.err = err
+	h.mu.Unlock()
+}