add OnUpgrade callback

Author: kokizzu

caddy.go

@@ -16,14 +16,14 @@
 //
 // To use this package:
 //
-//   1. Set the AppName and AppVersion variables.
-//   2. Call LoadCaddyfile() to get the Caddyfile.
-//      Pass in the name of the server type (like "http").
-//      Make sure the server type's package is imported
-//      (import _ "github.com/coredns/caddy/caddyhttp").
-//   3. Call caddy.Start() to start Caddy. You get back
-//      an Instance, on which you can call Restart() to
-//      restart it or Stop() to stop it.
+//  1. Set the AppName and AppVersion variables.
+//  2. Call LoadCaddyfile() to get the Caddyfile.
+//     Pass in the name of the server type (like "http").
+//     Make sure the server type's package is imported
+//     (import _ "github.com/coredns/caddy/caddyhttp").
+//  3. Call caddy.Start() to start Caddy. You get back
+//     an Instance, on which you can call Restart() to
+//     restart it or Stop() to stop it.
 //
 // You should call Wait() on your instance to wait for
 // all servers to quit before your process exits.
@@ -113,6 +113,7 @@ type Instance struct {
 	OnRestartFailed []func() error // if restart failed
 	OnShutdown      []func() error // stopping, even as part of a restart
 	OnFinalShutdown []func() error // stopping, not as part of a restart
+	OnUpgrade       []func() error // stopping, not as part of a shutdown
 
 	// storing values on an instance is preferable to
 	// global state because these will get garbage-

controller.go

@@ -104,6 +104,12 @@ func (c *Controller) OnFinalShutdown(fn func() error) {
 	c.instance.OnFinalShutdown = append(c.instance.OnFinalShutdown, fn)
 }
 
+// OnUpgrade adds fn to the list of callback functions to execute
+// when the plugin need to do something before upgrade (eg. release port)
+func (c *Controller) OnUpgrade(fn func() error) {
+	c.instance.OnUpgrade = append(c.instance.OnUpgrade, fn)
+}
+
 // Context gets the context associated with the instance associated with c.
 func (c *Controller) Context() Context {
 	return c.instance.context

upgrade.go

@@ -118,6 +118,13 @@ func Upgrade() error {
 				}
 			}
 		}
+
+		for i, onUpgradeFunc := range inst.OnUpgrade {
+			err := onUpgradeFunc()
+			if err != nil {
+				log.Printf("[WARN] OnUpgrade[%d] function returned error: %v", i, err)
+			}
+		}
 	}
 
 	// set up the command