API: Add user online stats (#3637)

* add statsUserOnline bool to policy

* add OnlineMap struct to stats

* apply UserOnline functionality to dispatcher

* add statsonline api command

* fix comments

* Update app/stats/online_map.go

Co-authored-by: mmmray <142015632+mmmray@users.noreply.github.com>

* improve AddIP

* regenerate pb

---------

Co-authored-by: mmmray <142015632+mmmray@users.noreply.github.com>

app/stats/online_map.go

@@ -0,0 +1,80 @@
+package stats
+
+import (
+	"sync"
+	"time"
+)
+
+// OnlineMap is an implementation of stats.OnlineMap.
+type OnlineMap struct {
+	value         int
+	ipList        map[string]time.Time
+	access        sync.RWMutex
+	lastCleanup   time.Time
+	cleanupPeriod time.Duration
+}
+
+// NewOnlineMap creates a new instance of OnlineMap.
+func NewOnlineMap() *OnlineMap {
+	return &OnlineMap{
+		ipList:        make(map[string]time.Time),
+		lastCleanup:   time.Now(),
+		cleanupPeriod: 10 * time.Second,
+	}
+}
+
+// Count implements stats.OnlineMap.
+func (c *OnlineMap) Count() int {
+	return c.value
+}
+
+// List implements stats.OnlineMap.
+func (c *OnlineMap) List() []string {
+	return c.GetKeys()
+}
+
+// AddIP implements stats.OnlineMap.
+func (c *OnlineMap) AddIP(ip string) {
+	list := c.ipList
+
+	if ip == "127.0.0.1" {
+		return
+	}
+	if _, ok := list[ip]; !ok {
+		c.access.Lock()
+		list[ip] = time.Now()
+		c.access.Unlock()
+	}
+	if time.Since(c.lastCleanup) > c.cleanupPeriod {
+		list = c.RemoveExpiredIPs(list)
+		c.lastCleanup = time.Now()
+	}
+
+	c.value = len(list)
+	c.ipList = list
+}
+
+func (c *OnlineMap) GetKeys() []string {
+	c.access.RLock()
+	defer c.access.RUnlock()
+
+	keys := []string{}
+	for k := range c.ipList {
+		keys = append(keys, k)
+	}
+	return keys
+}
+
+func (c *OnlineMap) RemoveExpiredIPs(list map[string]time.Time) map[string]time.Time {
+	c.access.Lock()
+	defer c.access.Unlock()
+
+	now := time.Now()
+	for k, t := range list {
+		diff := now.Sub(t)
+		if diff.Seconds() > 20 {
+			delete(list, k)
+		}
+	}
+	return list
+}