swarm/api/http: add error pages (#14967)

swarm/api/http/error.go

@@ -0,0 +1,116 @@
+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+/*
+Show nicely (but simple) formatted HTML error pages (or respond with JSON
+if the appropriate `Accept` header is set)) for the http package.
+*/
+package http
+
+import (
+	"encoding/json"
+	"fmt"
+	"html/template"
+	"net/http"
+	"time"
+
+	"github.com/ethereum/go-ethereum/log"
+)
+
+//templateMap holds a mapping of an HTTP error code to a template
+var templateMap map[int]*template.Template
+
+//parameters needed for formatting the correct HTML page
+type ErrorParams struct {
+	Msg       string
+	Code      int
+	Timestamp string
+	template  *template.Template
+	Details   template.HTML
+}
+
+//we init the error handling right on boot time, so lookup and http response is fast
+func init() {
+	initErrHandling()
+}
+
+func initErrHandling() {
+	//pages are saved as strings - get these strings
+	genErrPage := GetGenericErrorPage()
+	notFoundPage := GetNotFoundErrorPage()
+	//map the codes to the available pages
+	tnames := map[int]string{
+		0:   genErrPage, //default
+		400: genErrPage,
+		404: notFoundPage,
+		500: genErrPage,
+	}
+	templateMap = make(map[int]*template.Template)
+	for code, tname := range tnames {
+		//assign formatted HTML to the code
+		templateMap[code] = template.Must(template.New(fmt.Sprintf("%d", code)).Parse(tname))
+	}
+}
+
+//ShowError is used to show an HTML error page to a client.
+//If there is an `Accept` header of `application/json`, JSON will be returned instead
+//The function just takes a string message which will be displayed in the error page.
+//The code is used to evaluate which template will be displayed
+//(and return the correct HTTP status code)
+func ShowError(w http.ResponseWriter, r *http.Request, msg string, code int) {
+	if code == http.StatusInternalServerError {
+		log.Error(msg)
+	}
+	respond(w, r, &ErrorParams{
+		Code:      code,
+		Msg:       msg,
+		Timestamp: time.Now().Format(time.RFC1123),
+		template:  getTemplate(code),
+	})
+}
+
+//evaluate if client accepts html or json response
+func respond(w http.ResponseWriter, r *http.Request, params *ErrorParams) {
+	w.WriteHeader(params.Code)
+	if r.Header.Get("Accept") == "application/json" {
+		respondJson(w, params)
+	} else {
+		respondHtml(w, params)
+	}
+}
+
+//return a HTML page
+func respondHtml(w http.ResponseWriter, params *ErrorParams) {
+	err := params.template.Execute(w, params)
+	if err != nil {
+		log.Error(err.Error())
+	}
+}
+
+//return JSON
+func respondJson(w http.ResponseWriter, params *ErrorParams) {
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(params)
+}
+
+//get the HTML template for a given code
+func getTemplate(code int) *template.Template {
+	if val, tmpl := templateMap[code]; tmpl {
+		return val
+	} else {
+		return templateMap[0]
+	}
+}