add basic metrics (#966)

* add metrics

* change how counting works

* also replace dots

* check that metrics exist

* rename NullMetrics to nullMetrics

* update go.sum

* register collectors only once

* add tests

* add tests for metrics and fix bugs

* keep old metrics around for test

* properly reset during shutdown

* use the same method as frankenphp

* Revert "keep old metrics around for test"

This reverts commit 1f0df6f6bdaebf32aec346f068d6f42a0b5f4007.

* change to require.NoError

* compile regex only once

* remove name sanitizer

* use require

* parameterize host port because security software sucks

* remove need for renaming workers

* increase number of threads and add tests

* fix where frankenphp configuration was bleeding into later tests

* adds basic docs for metrics

* Add caddy metrics link

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

* Fix typos

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

* address feedback

* change comment to be much more "dangerous"

---------

Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

metrics_test.go

@@ -0,0 +1,82 @@
+package frankenphp
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stretchr/testify/require"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetWorkerNameForMetrics(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"worker-1", "worker_1"},
+		{"worker@name", "worker_name"},
+		{"worker name", "worker_name"},
+		{"worker/name", "worker_name"},
+		{"worker.name", "worker_name"},
+		{"////worker////name...//worker", "worker_name_worker"},
+	}
+
+	for _, test := range tests {
+		result := getWorkerNameForMetrics(test.input)
+		assert.Equal(t, test.expected, result)
+	}
+}
+
+func createPrometheusMetrics() *PrometheusMetrics {
+	return &PrometheusMetrics{
+		registry:           prometheus.NewRegistry(),
+		totalThreads:       prometheus.NewCounter(prometheus.CounterOpts{Name: "total_threads"}),
+		busyThreads:        prometheus.NewGauge(prometheus.GaugeOpts{Name: "busy_threads"}),
+		totalWorkers:       make(map[string]prometheus.Gauge),
+		busyWorkers:        make(map[string]prometheus.Gauge),
+		workerRequestTime:  make(map[string]prometheus.Counter),
+		workerRequestCount: make(map[string]prometheus.Counter),
+		mu:                 sync.Mutex{},
+	}
+}
+
+func TestPrometheusMetrics_TotalWorkers(t *testing.T) {
+	m := createPrometheusMetrics()
+
+	tests := []struct {
+		name   string
+		worker string
+		num    int
+	}{
+		{"SetWorkers", "test_worker", 5},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m.TotalWorkers(tt.worker, tt.num)
+			actualName, _ := m.getIdentity(tt.worker)
+			_, ok := m.totalWorkers[actualName]
+			require.True(t, ok)
+		})
+	}
+}
+
+func TestPrometheusMetrics_StopWorkerRequest(t *testing.T) {
+	m := createPrometheusMetrics()
+	m.StopWorkerRequest("test_worker", 2*time.Second)
+
+	name := "test_worker"
+	_, ok := m.workerRequestTime[name]
+	require.False(t, ok)
+}
+
+func TestPrometheusMetrics_StartWorkerRequest(t *testing.T) {
+	m := createPrometheusMetrics()
+	m.StartWorkerRequest("test_worker")
+
+	name := "test_worker"
+	_, ok := m.workerRequestCount[name]
+	require.False(t, ok)
+}