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.