hydra_oidc_poc/common/handlers/errors.go

package handlers

import (
	"context"
	"html/template"
	"net/http"
	"path"

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

	commonServices "git.cacert.org/oidc_login/common/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 *commonServices.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.Errorf("error rendering error template: %v", err)
			http.Error(
				w,
				http.StatusText(http.StatusInternalServerError),
				http.StatusInternalServerError,
			)
		}
	}
}

func GetErrorBucket(r *http.Request) *ErrorBucket {
	return r.Context().Value(errorBucketKey).(*ErrorBucket)
}

// call this from your application's handler
func (b *ErrorBucket) AddError(details *ErrorDetails) {
	b.errorDetails = details
}

type errorResponseWriter struct {
	http.ResponseWriter
	ctx        context.Context
	statusCode int
}

func (w *errorResponseWriter) WriteHeader(code int) {
	w.statusCode = code
	if code >= 400 {
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		errorBucket := w.ctx.Value(errorBucketKey).(*ErrorBucket)
		if errorBucket != nil && errorBucket.errorDetails == nil {
			errorBucket.AddError(&ErrorDetails{
				ErrorMessage: http.StatusText(code),
			})
		}
	}
	w.ResponseWriter.WriteHeader(code)
}

func (w *errorResponseWriter) Write(content []byte) (int, error) {
	if w.statusCode > 400 {
		errorBucket := w.ctx.Value(errorBucketKey).(*ErrorBucket)
		if errorBucket != nil {
			if errorBucket.errorDetails.ErrorDetails == nil {
				errorBucket.errorDetails.ErrorDetails = make([]string, 0)
			}
			errorBucket.errorDetails.ErrorDetails = append(
				errorBucket.errorDetails.ErrorDetails, string(content),
			)
			return len(content), nil
		}
	}
	return w.ResponseWriter.Write(content)
}

func ErrorHandling(
	handlerContext context.Context,
	logger *log.Logger,
	templateBaseDir string,
) (func(http.Handler) http.Handler, error) {
	errorTemplates, err := template.ParseFiles(
		path.Join(templateBaseDir, "base.gohtml"),
		path.Join(templateBaseDir, "errors.gohtml"),
	)
	if err != nil {
		return nil, 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:         commonServices.GetI18nBundle(handlerContext),
				messageCatalog: commonServices.GetMessageCatalog(handlerContext),
			}
			ctx := context.WithValue(r.Context(), errorBucketKey, errorBucket)
			interCeptingResponseWriter := &errorResponseWriter{
				w,
				ctx,
				http.StatusOK,
			}
			next.ServeHTTP(
				interCeptingResponseWriter,
				r.WithContext(ctx),
			)
			errorBucket.serveHTTP(w, r)
		})
	}, nil
}