Add structured logging and better error handling

internal/server/observe.go

@@ -0,0 +1,115 @@
+package server
+
+import (
+	"context"
+	"crypto/rand"
+	"encoding/hex"
+	"log/slog"
+	"net/http"
+	"runtime/debug"
+	"time"
+)
+
+type contextKey int
+
+const requestIDKey contextKey = iota
+
+type statusRecorder struct {
+	http.ResponseWriter
+	status int
+}
+
+func (recorder *statusRecorder) WriteHeader(status int) {
+	if recorder.status == 0 {
+		recorder.status = status
+	}
+	recorder.ResponseWriter.WriteHeader(status)
+}
+
+func (recorder *statusRecorder) Write(data []byte) (int, error) {
+	if recorder.status == 0 {
+		recorder.status = http.StatusOK
+	}
+	return recorder.ResponseWriter.Write(data)
+}
+
+func (recorder *statusRecorder) Unwrap() http.ResponseWriter {
+	return recorder.ResponseWriter
+}
+
+func (server *Server) observe(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(writer http.ResponseWriter, request *http.Request) {
+		started := time.Now()
+		requestID := newRequestID()
+		writer.Header().Set("X-Request-ID", requestID)
+		request = request.WithContext(context.WithValue(request.Context(), requestIDKey, requestID))
+		recorder := &statusRecorder{ResponseWriter: writer}
+
+		defer func() {
+			if recovered := recover(); recovered != nil {
+				if recovered == http.ErrAbortHandler {
+					panic(recovered)
+				}
+				slog.Error("request handler crashed",
+					"request_id", requestID,
+					"method", request.Method,
+					"path", request.URL.Path,
+					"panic", recovered,
+					"stack", string(debug.Stack()),
+				)
+				if recorder.status == 0 {
+					writeError(recorder, http.StatusInternalServerError, internalErrorMessage(requestID))
+				}
+			}
+			server.logRequest(request, recorder.status, time.Since(started))
+		}()
+
+		next.ServeHTTP(recorder, request)
+	})
+}
+
+func (server *Server) logRequest(request *http.Request, status int, duration time.Duration) {
+	if status == 0 {
+		status = http.StatusOK
+	}
+	slog.Log(request.Context(), requestLogLevel(request.Method, status), "request",
+		"request_id", requestIDFrom(request),
+		"method", request.Method,
+		"path", request.URL.Path,
+		"status", status,
+		"duration_ms", duration.Milliseconds(),
+		"client", server.clientAddress(request),
+	)
+}
+
+func requestLogLevel(method string, status int) slog.Level {
+	switch {
+	case status >= http.StatusInternalServerError:
+		return slog.LevelError
+	case status >= http.StatusBadRequest && status != http.StatusUnauthorized:
+		return slog.LevelWarn
+	case method != http.MethodGet && method != http.MethodHead:
+		return slog.LevelInfo
+	default:
+		return slog.LevelDebug
+	}
+}
+
+func requestIDFrom(request *http.Request) string {
+	if requestID, ok := request.Context().Value(requestIDKey).(string); ok {
+		return requestID
+	}
+	return ""
+}
+
+func newRequestID() string {
+	buffer := make([]byte, 6)
+	if _, err := rand.Read(buffer); err != nil {
+		return "unknown"
+	}
+	return hex.EncodeToString(buffer)
+}
+
+func internalErrorMessage(requestID string) string {
+	return "Something went wrong on the server (reference " + requestID + "). The server log has the details."
+}