From 3aa39d908a98b8f351f7e69c2bc0c45cca65dcc9 Mon Sep 17 00:00:00 2001
From: Troy Dai <git@troydai.com>
Date: Fri, 29 Nov 2024 11:33:59 -0800
Subject: [PATCH] [v1.4.2] Introduce normalized latency distribution

---
 internal/http/math.go         | 24 ++++++++++++++++++++++++
 internal/http/server.go       | 30 +++++++++++++++++++++++-------
 internal/settings/settings.go |  2 ++
 3 files changed, 49 insertions(+), 7 deletions(-)
 create mode 100644 internal/http/math.go

diff --git a/internal/http/math.go b/internal/http/math.go
new file mode 100644
index 0000000..266500f
--- /dev/null
+++ b/internal/http/math.go
@@ -0,0 +1,24 @@
+package http
+
+import (
+	"math/rand"
+	"time"
+)
+
+type normalDistribution struct {
+	mean   float64
+	stddev float64
+}
+
+func newNormalDistribution(mean, stddev uint64) *normalDistribution {
+	return &normalDistribution{mean: float64(mean), stddev: float64(stddev)}
+}
+
+func (n *normalDistribution) latency() time.Duration {
+	ms := n.mean + rand.NormFloat64()*n.stddev
+	if ms < 0 {
+		return 0
+	}
+
+	return time.Duration(ms) * time.Millisecond
+}
diff --git a/internal/http/server.go b/internal/http/server.go
index e73d348..d144157 100644
--- a/internal/http/server.go
+++ b/internal/http/server.go
@@ -5,6 +5,7 @@ import (
 	"log/slog"
 	"net/http"
 	"sync/atomic"
+	"time"
 
 	"go.uber.org/fx"
 
@@ -18,21 +19,36 @@ var Module = fx.Options(
 
 func ProvideServer(s *settings.Values, l *slog.Logger) *Server {
 	return &Server{
-		counter:   &atomic.Uint64{},
-		frequency: s.CrashFrequency,
-		logger:    l,
+		counter:    &atomic.Uint64{},
+		frequency:  s.CrashFrequency,
+		logger:     l,
+		latencyGen: newNormalDistribution(s.LatencyMean, s.LatencyStddev),
 	}
 }
 
 type Server struct {
-	counter   *atomic.Uint64
-	frequency uint64
-	logger    *slog.Logger
+	counter    *atomic.Uint64
+	frequency  uint64
+	logger     *slog.Logger
+	latencyGen *normalDistribution
 }
 
 func (s *Server) HandleHTTP(w http.ResponseWriter, r *http.Request) {
-	s.logger.Info("inbound", "method", r.Method, "url", r.URL.Path, "host", r.Host, "proto", r.Proto, "agent", r.UserAgent(), "peer", r.RemoteAddr, "counter", s.counter.Load())
 	newCount := s.counter.Add(1)
+	latency := s.latencyGen.latency()
+
+	s.logger.Info("inbound",
+		"method", r.Method,
+		"url", r.URL.Path,
+		"host", r.Host,
+		"proto", r.Proto,
+		"agent", r.UserAgent(),
+		"peer", r.RemoteAddr,
+		"counter", newCount,
+		"latency", latency,
+	)
+
+	time.Sleep(s.latencyGen.latency())
 
 	if s.frequency != 0 && newCount%s.frequency == 0 {
 		s.logger.Warn("crash", "counter", newCount)
diff --git a/internal/settings/settings.go b/internal/settings/settings.go
index d67534c..0887db4 100644
--- a/internal/settings/settings.go
+++ b/internal/settings/settings.go
@@ -11,6 +11,8 @@ var Module = fx.Provide(ProvideSettings)
 
 type Values struct {
 	CrashFrequency uint64 `env:"HTTP_CRASH_FREQUENCY" envDefault:"10"` // Set to zero to disable
+	LatencyMean    uint64 `env:"HTTP_LATENCY_MEAN" envDefault:"50"`
+	LatencyStddev  uint64 `env:"HTTP_LATENCY_STDDEV" envDefault:"25"`
 }
 
 func ProvideSettings() (*Values, error) {