oidc-demo-app/handlers/errors.go

/*
Copyright 2020-2023 CAcert Inc.
SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package handlers

import (
	"context"
	"fmt"
	"html/template"
	"io/fs"
	"net/http"

	"github.com/nicksnyder/go-i18n/v2/i18n"
	log "github.com/sirupsen/logrus"

	"code.cacert.org/cacert/oidc-demo-app/services"
)

type errorKey int

const (
	errorBucketKey errorKey = iota
)

type ErrorDetails struct {
	ErrorMessage string
	ErrorDetails []string
	ErrorCode    string
	Error        error
}

type ErrorBucket struct {
	errorDetails   *ErrorDetails
	templates      *template.Template
	logger         *log.Logger
	bundle         *i18n.Bundle
	messageCatalog *services.MessageCatalog
}

func (b *ErrorBucket) serveHTTP(w http.ResponseWriter, r *http.Request) {
	if b.errorDetails != nil {
		accept := r.Header.Get("Accept-Language")
		localizer := i18n.NewLocalizer(b.bundle, accept)

		err := b.templates.Lookup("base").Execute(w, map[string]interface{}{
			"Title": b.messageCatalog.LookupMessage(
				"ErrorTitle",
				nil,
				localizer,
			),
			"details": b.errorDetails,
		})
		if err != nil {
			log.WithError(err).Error("error rendering error template")
			http.Error(
				w,
				http.StatusText(http.StatusInternalServerError),
				http.StatusInternalServerError,
			)
		}
	}
}

func GetErrorBucket(r *http.Request) *ErrorBucket {
	if v, ok := r.Context().Value(errorBucketKey).(*ErrorBucket); ok {
		return v
	}

	return nil
}

// AddError can be called from an application handler to add an error
func (b *ErrorBucket) AddError(details *ErrorDetails) {
	b.errorDetails = details
}

type errorResponseWriter struct {
	http.ResponseWriter
	errorBucket *ErrorBucket
	statusCode  int
}

func (w *errorResponseWriter) WriteHeader(code int) {
	w.statusCode = code

	if code >= http.StatusBadRequest {
		w.Header().Set("Content-Type", "text/html; charset=utf-8")

		if w.errorBucket != nil && w.errorBucket.errorDetails == nil {
			w.errorBucket.AddError(&ErrorDetails{
				ErrorMessage: http.StatusText(code),
			})
		}
	}

	w.ResponseWriter.WriteHeader(code)
}

func (w *errorResponseWriter) Write(content []byte) (int, error) {
	if w.statusCode > http.StatusBadRequest {
		if w.errorBucket != nil {
			if w.errorBucket.errorDetails.ErrorDetails == nil {
				w.errorBucket.errorDetails.ErrorDetails = make([]string, 0)
			}

			w.errorBucket.errorDetails.ErrorDetails = append(
				w.errorBucket.errorDetails.ErrorDetails, string(content),
			)

			return len(content), nil
		}
	}

	l, err := w.ResponseWriter.Write(content)
	if err != nil {
		return l, fmt.Errorf("could not write to response: %w", err)
	}

	return l, nil
}

func ErrorHandling(
	logger *log.Logger,
	templateFS fs.FS,
	bundle *i18n.Bundle,
	messageCatalog *services.MessageCatalog,
) (func(http.Handler) http.Handler, error) {
	errorTemplates, err := template.ParseFS(
		templateFS,
		"templates/base.gohtml",
		"templates/errors.gohtml",
	)
	if err != nil {
		return nil, fmt.Errorf("could not parse templates: %w", err)
	}

	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
			errorBucket := &ErrorBucket{
				templates:      errorTemplates,
				logger:         logger,
				bundle:         bundle,
				messageCatalog: messageCatalog,
			}
			next.ServeHTTP(
				&errorResponseWriter{w, errorBucket, http.StatusOK},
				r.WithContext(context.WithValue(r.Context(), errorBucketKey, errorBucket)),
			)
			errorBucket.serveHTTP(w, r)
		})
	}, nil
}