TUN-7133: Add sampling support for streaming logs

In addition to supporting sampling support for streaming logs,
cloudflared tail also supports this via `--sample 0.5` to sample 50%
of your log events.

management/events.go

@@ -52,8 +52,9 @@ type EventStartStreaming struct {
 }
 
 type StreamingFilters struct {
-	Events []LogEventType `json:"events,omitempty"`
-	Level  *LogLevel      `json:"level,omitempty"`
+	Events   []LogEventType `json:"events,omitempty"`
+	Level    *LogLevel      `json:"level,omitempty"`
+	Sampling float64        `json:"sampling,omitempty"`
 }
 
 // EventStopStreaming signifies that the client wishes to halt receiving log events.

management/events_test.go

@@ -57,13 +57,23 @@ func TestIntoClientEvent_StartStreaming(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "sampling filter",
+			expected: EventStartStreaming{
+				ClientEvent: ClientEvent{Type: StartStreaming},
+				Filters: &StreamingFilters{
+					Sampling: 0.5,
+				},
+			},
+		},
 		{
 			name: "level and events filters",
 			expected: EventStartStreaming{
 				ClientEvent: ClientEvent{Type: StartStreaming},
 				Filters: &StreamingFilters{
-					Level:  infoLevel,
-					Events: []LogEventType{Cloudflared},
+					Level:    infoLevel,
+					Events:   []LogEventType{Cloudflared},
+					Sampling: 0.5,
 				},
 			},
 		},

management/session.go

@@ -2,6 +2,7 @@ package management
 
 import (
 	"context"
+	"math/rand"
 	"sync/atomic"
 )
 
@@ -25,6 +26,8 @@ type session struct {
 	listener chan *Log
 	// Types of log events that this session will provide through the listener
 	filters *StreamingFilters
+	// Sampling of the log events this session will send (runs after all other filters if available)
+	sampler *sampler
 }
 
 // NewSession creates a new session.
@@ -43,6 +46,20 @@ func newSession(size int, actor actor, cancel context.CancelFunc) *session {
 func (s *session) Filters(filters *StreamingFilters) {
 	if filters != nil {
 		s.filters = filters
+		sampling := filters.Sampling
+		// clamp the sampling values between 0 and 1
+		if sampling < 0 {
+			sampling = 0
+		}
+		if sampling > 1 {
+			sampling = 1
+		}
+		s.filters.Sampling = sampling
+		if sampling > 0 && sampling < 1 {
+			s.sampler = &sampler{
+				p: int(sampling * 100),
+			}
+		}
 	} else {
 		s.filters = &StreamingFilters{}
 	}
@@ -61,6 +78,10 @@ func (s *session) Insert(log *Log) {
 	if len(s.filters.Events) != 0 && !contains(s.filters.Events, log.Event) {
 		return
 	}
+	// Sampling is also optional
+	if s.sampler != nil && !s.sampler.Sample() {
+		return
+	}
 	select {
 	case s.listener <- log:
 	default:
@@ -86,3 +107,14 @@ func contains(array []LogEventType, t LogEventType) bool {
 	}
 	return false
 }
+
+// sampler will send approximately every p percentage log events out of 100.
+type sampler struct {
+	p int
+}
+
+// Sample returns true if the event should be part of the sample, false if the event should be dropped.
+func (s *sampler) Sample() bool {
+	return rand.Intn(100) <= s.p
+
+}

management/session_test.go

@@ -67,6 +67,27 @@ func TestSession_Insert(t *testing.T) {
 			},
 			expectLog: false,
 		},
+		{
+			name: "sampling",
+			filters: StreamingFilters{
+				Sampling: 0.9999999,
+			},
+			expectLog: true,
+		},
+		{
+			name: "sampling (invalid negative)",
+			filters: StreamingFilters{
+				Sampling: -1.0,
+			},
+			expectLog: true,
+		},
+		{
+			name: "sampling (invalid too large)",
+			filters: StreamingFilters{
+				Sampling: 2.0,
+			},
+			expectLog: true,
+		},
 		{
 			name: "filter and event",
 			filters: StreamingFilters{