separate out error handler

handler/error_handler.go

@@ -0,0 +1,66 @@
+package handler
+
+import (
+	"bytes"
+	"log"
+	"maps"
+	"net/http"
+	"net/http/httptest"
+	"slices"
+
+	"codeberg.org/vnpower/pixivfe/v2/routes"
+)
+
+type UserContext struct {
+	Err        error
+	StatusCode int
+}
+
+type userContextKey struct{}
+
+var UserContextKey = userContextKey{}
+
+func GetUserContext(r *http.Request) *UserContext {
+	return r.Context().Value(UserContextKey).(*UserContext)
+}
+
+func CatchError(handler func(w http.ResponseWriter, r *http.Request) error) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		header_backup := http.Header{}
+		for k, v := range w.Header() {
+			header_backup[k] = slices.Clone(v)
+		}
+		recorder := httptest.ResponseRecorder{
+			HeaderMap: w.Header(),
+			Body:      new(bytes.Buffer),
+			Code:      200,
+		}
+		err := handler(&recorder, r)
+		if err != nil {
+			clear(header_backup)
+			maps.Copy(w.Header(), header_backup)
+			GetUserContext(r).Err = err
+		} else {
+			_, _ = recorder.Body.WriteTo(w)
+			w.WriteHeader(recorder.Code)
+		}
+	}
+}
+
+func ErrorHandler(w http.ResponseWriter, r *http.Request) { // error handler
+	err := GetUserContext(r).Err
+
+	if err != nil {
+		log.Printf("Internal Server Error: %s", err)
+		code := GetUserContext(r).StatusCode
+		if code == 0 {
+			code = http.StatusInternalServerError
+		}
+		w.WriteHeader(code)
+		// Send custom error page
+		err = routes.ErrorPage(w, r, err)
+		if err != nil {
+			log.Printf("Error rendering error route: %s", err)
+		}
+	}
+}