errors.go

package beyond

import (
	"flag"
	"fmt"
	"html/template"
	"net/http"
)

var (
	errorColor = flag.String("error-color", "#69b342", "css h1 color for errors")
	errorEmail = flag.String("error-email", "", "address for help (eg. support@mycompany.com)")
	errorPlain = flag.Bool("error-plain", false, "disable html on error pages")

	errorTemplate = template.Must(template.New("error").Parse(`<!DOCTYPE html>
<html lang="en">
	<head>
		<!-- Simple HttpErrorPages | MIT License | https://github.com/AndiDittrich/HttpErrorPages -->
		<meta charset="utf-8" /><meta http-equiv="X-UA-Compatible" content="IE=edge" /><meta name="viewport" content="width=device-width, initial-scale=1" />
		<title>{{.code}} - {{.title}}</title>
		<style type="text/css">/*! normalize.css v5.0.0 | MIT License | github.com/necolas/normalize.css */html{font-family:sans-serif;line-height:1.15;-ms-text-size-adjust:100%;-webkit-text-size-adjust:100%}body{margin:0}article,aside,footer,header,nav,section{display:block}h1{font-size:2em;margin:.67em 0}figcaption,figure,main{display:block}figure{margin:1em 40px}hr{box-sizing:content-box;height:0;overflow:visible}pre{font-family:monospace,monospace;font-size:1em}a{background-color:transparent;-webkit-text-decoration-skip:objects}a:active,a:hover{outline-width:0}abbr[title]{border-bottom:none;text-decoration:underline;text-decoration:underline dotted}b,strong{font-weight:inherit}b,strong{font-weight:bolder}code,kbd,samp{font-family:monospace,monospace;font-size:1em}dfn{font-style:italic}mark{background-color:#ff0;color:#000}small{font-size:80%}sub,sup{font-size:75%;line-height:0;position:relative;vertical-align:baseline}sub{bottom:-.25em}sup{top:-.5em}audio,video{display:inline-block}audio:not([controls]){display:none;height:0}img{border-style:none}svg:not(:root){overflow:hidden}button,input,optgroup,select,textarea{font-family:sans-serif;font-size:100%;line-height:1.15;margin:0}button,input{overflow:visible}button,select{text-transform:none}[type=reset],[type=submit],button,html [type=button]{-webkit-appearance:button}[type=button]::-moz-focus-inner,[type=reset]::-moz-focus-inner,[type=submit]::-moz-focus-inner,button::-moz-focus-inner{border-style:none;padding:0}[type=button]:-moz-focusring,[type=reset]:-moz-focusring,[type=submit]:-moz-focusring,button:-moz-focusring{outline:1px dotted ButtonText}fieldset{border:1px solid silver;margin:0 2px;padding:.35em .625em .75em}legend{box-sizing:border-box;color:inherit;display:table;max-width:100%;padding:0;allow-space:normal}progress{display:inline-block;vertical-align:baseline}textarea{overflow:auto}[type=checkbox],[type=radio]{box-sizing:border-box;padding:0}[type=number]::-webkit-inner-spin-button,[type=number]::-webkit-outer-spin-button{height:auto}[type=search]{-webkit-appearance:textfield;outline-offset:-2px}[type=search]::-webkit-search-cancel-button,[type=search]::-webkit-search-decoration{-webkit-appearance:none}::-webkit-file-upload-button{-webkit-appearance:button;font:inherit}details,menu{display:block}summary{display:list-item}canvas{display:inline-block}template{display:none}[hidden]{display:none}/*! Simple HttpErrorPages | MIT X11 License | https://github.com/AndiDittrich/HttpErrorPages */body,html{width:100%;height:100%;background-color:#21232a}body{color:{{.color}};text-align:center;text-shadow:0 2px 4px rgba(0,0,0,.5);padding:0;min-height:100%;-webkit-box-shadow:inset 0 0 100px rgba(0,0,0,.8);box-shadow:inset 0 0 100px rgba(0,0,0,.8);display:table;font-family:"Open Sans",Arial,sans-serif}h1{font-family:inherit;font-weight:500;line-height:1.1;color:inherit;font-size:36px}h1 small{font-size:68%;font-weight:400;line-height:1;color:#777}a{text-decoration:none;color:#fff;font-size:inherit;border-bottom:dotted 1px #707070}.lead{color:silver;font-size:21px;line-height:1.4}.cover{display:table-cell;vertical-align:middle;padding:0 20px}footer{position:fixed;width:100%;height:40px;left:0;bottom:0;color:#a0a0a0;font-size:14px}</style>
	</head>
	<body>
		<div class="cover"><h1>{{.title}} <small>Error {{.code}}</small></h1>{{if .description}}<p class="lead">{{.description}}</p>{{end}}</div>
		{{if .email}}<footer><p>Technical Contact: <a href="mailto:{{.email}}">{{.email}}</a></p></footer>{{end}}
	</body>
</html>`))
)

func errorExecute(w http.ResponseWriter, status int, description string) error {
	w.WriteHeader(status)
	if *errorPlain {
		_, err := fmt.Fprintln(w, description)
		return err
	}

	w.Header().Set("Content-Type", "text/html")
	setCacheControl(w)

	data := map[string]interface{}{
		"code":  fmt.Sprint(status),
		"title": http.StatusText(status),
		"color": *errorColor,
	}
	if description != "" {
		data["description"] = description
	}
	if *errorEmail != "" {
		data["email"] = *errorEmail
	}
	return errorTemplate.Execute(w, data)
}

func errorHandler(w http.ResponseWriter, status int, description string) {
	err := errorExecute(w, status, description)
	if err != nil {
		WithField("code", status).WithField("err", err.Error()).Error(description)
	}
}

// https://tools.ietf.org/html/rfc6749#section-4.1.2.1

func errorQuery(w http.ResponseWriter, r *http.Request) {
	errorDescription := r.URL.Query().Get("error_description")

	switch r.URL.Query().Get("error") {

	case "invalid_request":
		errorHandler(w, 400, errorDescription)

	case "access_denied", "unauthorized_client":
		errorHandler(w, 403, errorDescription)

	case "invalid_resource":
		errorHandler(w, 404, errorDescription)

	case "server_error":
		errorHandler(w, 500, errorDescription)

	case "unsupported_response_type":
		errorHandler(w, 501, errorDescription)

	case "temporarily_unavailable":
		errorHandler(w, 503, errorDescription)

	default:
		if errorDescription == "" {
			errorDescription = "Unknown Error"
		}
		errorHandler(w, 500, errorDescription)

	}
}