Add Honeybadger.io observability support.

It's not yet clear how useful it is, but it's at least something.

src/health.go

@@ -6,6 +6,15 @@ import (
 )
 
 func ServeHealth(w http.ResponseWriter, r *http.Request) {
-	w.WriteHeader(http.StatusOK)
-	fmt.Fprintln(w, "ok")
+	switch r.URL.Path {
+	case "/":
+		w.WriteHeader(http.StatusOK)
+		fmt.Fprintln(w, "ok")
+
+	case "/panic":
+		panic("explicit panic request")
+
+	default:
+		http.Error(w, "not found", http.StatusNotFound)
+	}
 }

src/main.go

@@ -2,11 +2,13 @@ package main
 
 import (
 	"flag"
+	"fmt"
 	"log"
 	"log/slog"
 	"net"
 	"net/http"
 	"os"
+	"runtime/debug"
 	"strings"
 
 	"github.com/KimMachineGun/automemlimit/memlimit"
@@ -32,17 +34,37 @@ func listen(name string, listen string) net.Listener {
 	return listener
 }
 
+func panicHandler(handler http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		defer func() {
+			if err := recover(); err != nil {
+				log.Printf("panic: %s %s %s: %s\n%s",
+					r.Method, r.Host, r.URL.Path, err, string(debug.Stack()))
+				http.Error(w,
+					fmt.Sprintf("internal server error: %s", err),
+					http.StatusInternalServerError,
+				)
+			}
+		}()
+		handler.ServeHTTP(w, r)
+	})
+}
+
 func serve(listener net.Listener, serve func(http.ResponseWriter, *http.Request)) {
 	if listener != nil {
-		if err := http.Serve(listener, http.HandlerFunc(serve)); err != nil {
-			log.Fatalln(err)
-		}
+		var handler http.Handler
+		handler = http.HandlerFunc(serve)
+		handler = ObserveHTTPHandler(handler)
+		handler = panicHandler(handler)
+		log.Fatalln(http.Serve(listener, handler))
 	}
 }
 
 func main() {
 	var err error
 
+	InitObservability()
+
 	configPath := flag.String("config", "config.toml", "path to configuration file")
 	migrateV1Path := flag.String("migrate-v1", "", "path to v1 data directory to upload")
 	flag.Parse()

src/observe.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"net/http"
+	"os"
+	"runtime/debug"
+
+	"github.com/honeybadger-io/honeybadger-go"
+)
+
+func hasHoneybadger() bool {
+	return os.Getenv("HONEYBADGER_API_KEY") != ""
+}
+
+func InitObservability() {
+	if hasHoneybadger() {
+		honeybadger.Configure(honeybadger.Configuration{})
+		debug.SetPanicOnFault(true)
+	}
+}
+
+func ObserveHTTPHandler(handler http.Handler) http.Handler {
+	if hasHoneybadger() {
+		handler = honeybadger.Handler(handler)
+	}
+	return handler
+}