path: root/swarm/api/http/error.go

// 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"
    "strings"
    "time"

    "github.com/ethereum/go-ethereum/log"
    "github.com/ethereum/go-ethereum/swarm/api"
)

//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()
    multipleChoicesPage := GetMultipleChoicesErrorPage()
    //map the codes to the available pages
    tnames := map[int]string{
        0: genErrPage, //default
        http.StatusBadRequest:          genErrPage,
        http.StatusNotFound:            notFoundPage,
        http.StatusMultipleChoices:     multipleChoicesPage,
        http.StatusInternalServerError: 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))
    }
}

//ShowMultipeChoices is used when a user requests a resource in a manifest which results
//in ambiguous results. It returns a HTML page with clickable links of each of the entry
//in the manifest which fits the request URI ambiguity.
//For example, if the user requests bzz:/<hash>/read and that manifest contains entries
//"readme.md" and "readinglist.txt", a HTML page is returned with this two links.
//This only applies if the manifest has no default entry
func ShowMultipleChoices(w http.ResponseWriter, r *http.Request, list api.ManifestList) {
    msg := ""
    if list.Entries == nil {
        ShowError(w, r, "Internal Server Error", http.StatusInternalServerError)
        return
    }
    //make links relative
    //requestURI comes with the prefix of the ambiguous path, e.g. "read" for "readme.md" and "readinglist.txt"
    //to get clickable links, need to remove the ambiguous path, i.e. "read"
    idx := strings.LastIndex(r.RequestURI, "/")
    if idx == -1 {
        ShowError(w, r, "Internal Server Error", http.StatusInternalServerError)
        return
    }
    //remove ambiguous part
    base := r.RequestURI[:idx+1]
    for _, e := range list.Entries {
        //create clickable link for each entry
        msg += "<a href='" + base + e.Path + "'>" + e.Path + "</a><br/>"
    }
    respond(w, r, &ErrorParams{
        Code:      http.StatusMultipleChoices,
        Details:   template.HTML(msg),
        Timestamp: time.Now().Format(time.RFC1123),
        template:  getTemplate(http.StatusMultipleChoices),
    })
}

//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]
    }
}