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>

configuration/configuration.go

@@ -29,6 +29,10 @@ type Configuration struct {
 		// Fields allows users to specify static string fields to include in
 		// the logger context.
 		Fields map[string]interface{} `yaml:"fields,omitempty"`
+
+		// Hooks allows users to configurate the log hooks, to enabling the
+		// sequent handling behavior, when defined levels of log message emit.
+		Hooks []LogHook `yaml:"hooks,omitempty"`
 	}
 
 	// Loglevel is the level at which registry operations are logged. This is
@@ -126,6 +130,47 @@ type Configuration struct {
 	} `yaml:"redis,omitempty"`
 }
 
+// LogHook is composed of hook Level and Type.
+// After hooks configuration, it can execute the next handling automatically,
+// when defined levels of log message emitted.
+// Example: hook can sending an email notification when error log happens in app.
+type LogHook struct {
+	// Disable lets user select to enable hook or not.
+	Disabled bool `yaml:"disabled,omitempty"`
+
+	// Type allows user to select which type of hook handler they want.
+	Type string `yaml:"type,omitempty"`
+
+	// Levels set which levels of log message will let hook executed.
+	Levels []string `yaml:"levels,omitempty"`
+
+	// MailOptions allows user to configurate email parameters.
+	MailOptions MailOptions `yaml:"options,omitempty"`
+}
+
+// MailOptions provides the configuration sections to user, for specific handler.
+type MailOptions struct {
+	SMTP struct {
+		// Addr defines smtp host address
+		Addr string `yaml:"addr,omitempty"`
+
+		// Username defines user name to smtp host
+		Username string `yaml:"username,omitempty"`
+
+		// Password defines password of login user
+		Password string `yaml:"password,omitempty"`
+
+		// Insecure defines if smtp login skips the secure cerification.
+		Insecure bool `yaml:"insecure,omitempty"`
+	} `yaml:"smtp,omitempty"`
+
+	// From defines mail sending address
+	From string `yaml:"from,omitempty"`
+
+	// To defines mail receiving address
+	To []string `yaml:"to,omitempty"`
+}
+
 // v0_1Configuration is a Version 0.1 Configuration struct
 // This is currently aliased to Configuration, as it is the current version
 type v0_1Configuration Configuration