Feature: Web Panic Reporting via hooks

This PR is for issue of "email after registry webapp panic" #41, improving my
previous design (closed).
It use self setting up hooks, to catch panic in web application.
And, send email in hooks handle directly, to no use new http server and
handler.

Signed-off-by: xiekeyang <keyangxie@126.com>

docs/handlers/app.go

@@ -9,6 +9,7 @@ import (
 	"os"
 	"time"
 
+	log "github.com/Sirupsen/logrus"
 	"github.com/docker/distribution"
 	"github.com/docker/distribution/configuration"
 	ctxu "github.com/docker/distribution/context"
@@ -101,6 +102,7 @@ func NewApp(ctx context.Context, configuration configuration.Configuration) *App
 
 	app.configureEvents(&configuration)
 	app.configureRedis(&configuration)
+	app.configureLogHook(&configuration)
 
 	// configure storage caches
 	if cc, ok := configuration.Storage["cache"]; ok {
@@ -291,6 +293,31 @@ func (app *App) configureRedis(configuration *configuration.Configuration) {
 	}))
 }
 
+// configureLogHook prepares logging hook parameters.
+func (app *App) configureLogHook(configuration *configuration.Configuration) {
+	logger := ctxu.GetLogger(app).(*log.Entry).Logger
+	for _, configHook := range configuration.Log.Hooks {
+		if !configHook.Disabled {
+			switch configHook.Type {
+			case "mail":
+				hook := &logHook{}
+				hook.LevelsParam = configHook.Levels
+				hook.Mail = &mailer{
+					Addr:     configHook.MailOptions.SMTP.Addr,
+					Username: configHook.MailOptions.SMTP.Username,
+					Password: configHook.MailOptions.SMTP.Password,
+					Insecure: configHook.MailOptions.SMTP.Insecure,
+					From:     configHook.MailOptions.From,
+					To:       configHook.MailOptions.To,
+				}
+				logger.Hooks.Add(hook)
+			default:
+			}
+		}
+	}
+	app.Context = ctxu.WithLogger(app.Context, logger)
+}
+
 func (app *App) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	defer r.Body.Close() // ensure that request body is always closed.
 

docs/handlers/hooks.go

@@ -0,0 +1,53 @@
+package handlers
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"strings"
+	"text/template"
+
+	"github.com/Sirupsen/logrus"
+)
+
+// logHook is for hooking Panic in web application
+type logHook struct {
+	LevelsParam []string
+	Mail        *mailer
+}
+
+// Fire forwards an error to LogHook
+func (hook *logHook) Fire(entry *logrus.Entry) error {
+	addr := strings.Split(hook.Mail.Addr, ":")
+	if len(addr) != 2 {
+		return errors.New("Invalid Mail Address")
+	}
+	host := addr[0]
+	subject := fmt.Sprintf("[%s] %s: %s", entry.Level, host, entry.Message)
+
+	html := `
+	{{.Message}}
+
+	{{range $key, $value := .Data}}
+	{{$key}}: {{$value}}
+	{{end}}
+	`
+	b := bytes.NewBuffer(make([]byte, 0))
+	t := template.Must(template.New("mail body").Parse(html))
+	if err := t.Execute(b, entry); err != nil {
+		return err
+	}
+	body := fmt.Sprintf("%s", b)
+
+	return hook.Mail.sendMail(subject, body)
+}
+
+// Levels contains hook levels to be catched
+func (hook *logHook) Levels() []logrus.Level {
+	levels := []logrus.Level{}
+	for _, v := range hook.LevelsParam {
+		lv, _ := logrus.ParseLevel(v)
+		levels = append(levels, lv)
+	}
+	return levels
+}

docs/handlers/mail.go

@@ -0,0 +1,45 @@
+package handlers
+
+import (
+	"errors"
+	"net/smtp"
+	"strings"
+)
+
+// mailer provides fields of email configuration for sending.
+type mailer struct {
+	Addr, Username, Password, From string
+	Insecure                       bool
+	To                             []string
+}
+
+// sendMail allows users to send email, only if mail parameters is configured correctly.
+func (mail *mailer) sendMail(subject, message string) error {
+	addr := strings.Split(mail.Addr, ":")
+	if len(addr) != 2 {
+		return errors.New("Invalid Mail Address")
+	}
+	host := addr[0]
+	msg := []byte("To:" + strings.Join(mail.To, ";") +
+		"\r\nFrom: " + mail.From +
+		"\r\nSubject: " + subject +
+		"\r\nContent-Type: text/plain\r\n\r\n" +
+		message)
+	auth := smtp.PlainAuth(
+		"",
+		mail.Username,
+		mail.Password,
+		host,
+	)
+	err := smtp.SendMail(
+		mail.Addr,
+		auth,
+		mail.From,
+		mail.To,
+		[]byte(msg),
+	)
+	if err != nil {
+		return err
+	}
+	return nil
+}