From ab579128b94a10dc3603a579d8b8ffba78153e62 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ask=20Bj=C3=B8rn=20Hansen?= <ask@develooper.com>
Date: Sun, 2 Jul 2023 23:49:05 -0700
Subject: [PATCH] health: basic health checker from the monitor

---
 health/health_server.go | 47 +++++++++++++++++++++++++++++++++++++++++
 health/health_test.go   | 27 +++++++++++++++++++++++
 2 files changed, 74 insertions(+)
 create mode 100644 health/health_server.go
 create mode 100644 health/health_test.go

diff --git a/health/health_server.go b/health/health_server.go
new file mode 100644
index 0000000..4cb064f
--- /dev/null
+++ b/health/health_server.go
@@ -0,0 +1,47 @@
+package health
+
+import (
+	"context"
+	"net/http"
+	"strconv"
+	"time"
+
+	"golang.org/x/exp/slog"
+)
+
+// HealthCheckListener runs simple http server on the specified port for
+// health check probes
+func HealthCheckListener(ctx context.Context, port int, log *slog.Logger) {
+	log.Info("Starting health listener", "port", port)
+
+	serveMux := http.NewServeMux()
+
+	serveMux.HandleFunc("/__health", basicHealth)
+
+	srv := &http.Server{
+		Addr:         ":" + strconv.Itoa(port),
+		ReadTimeout:  10 * time.Second,
+		WriteTimeout: 20 * time.Second,
+		IdleTimeout:  120 * time.Second,
+		Handler:      serveMux,
+	}
+
+	go func() {
+		err := srv.ListenAndServe()
+		if err != http.ErrServerClosed {
+			log.Warn("health check server done listening", "err", err)
+		}
+	}()
+
+	<-ctx.Done()
+
+	if err := srv.Shutdown(ctx); err != nil {
+		log.Error("health check server shutdown failed", "err", err)
+	}
+
+}
+
+func basicHealth(w http.ResponseWriter, r *http.Request) {
+	w.WriteHeader(200)
+	w.Write([]byte("ok"))
+}
diff --git a/health/health_test.go b/health/health_test.go
new file mode 100644
index 0000000..dfee501
--- /dev/null
+++ b/health/health_test.go
@@ -0,0 +1,27 @@
+package health
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestHealthHandler(t *testing.T) {
+
+	req := httptest.NewRequest(http.MethodGet, "/__health", nil)
+	w := httptest.NewRecorder()
+
+	basicHealth(w, req)
+
+	res := w.Result()
+	defer res.Body.Close()
+	data, err := io.ReadAll(res.Body)
+	if err != nil {
+		t.Errorf("expected error to be nil got %v", err)
+	}
+	if string(data) != "ok" {
+		t.Fail()
+		t.Errorf("expected ok got %q", string(data))
+	}
+}