Glean

A go plugin framework that can reload variables and functions from plugins automatically.

Installation

go get -u github.com/smallnest/glean

Feature

• load symbol and you don't worry about errors
• load/reload exported variables and funtions from plugins
• watch plugins' changes and reload pointer of variables and function in applications

Notice glean only can reload functions or variables that can be addresses.

Examples

see Examples

Let's look the httpserver example to learn how to use glean.

httpserver

httpserver is a very very simple http server.

A simple http server is just like this:

var FooHandler = func(w http.ResponseWriter, r *http.Request) {
	fmt.Fprint(w, "Hello, world")
}

http.Handle("/foo", fooHandler)

log.Fatal(http.ListenAndServe(":9988", nil))

Our goal is to replace fooHandler with latest code dynamically (hot fix).

var FooHandler = func(w http.ResponseWriter, r *http.Request) {
	fmt.Fprint(w, "Hello, gp")
}

No need to restart this server.

step1: build the two plugin

enter _example/httpserver/plugins/plugin1 and _example/httpserver/plugins/plugin2, and run the build.sh to generate the so file.

Currently plugin supports linux and MacOS.

step2: modify the server implementation

package main

import (
	"log"
	"net/http"

	"github.com/smallnest/glean"
)

func main() {
	g := glean.New("plugin.json")
	err := g.LoadConfig()
	if err != nil {
		panic(err)
	}

	var fooHandler func(w http.ResponseWriter, r *http.Request)

	err = g.ReloadAndWatch("FooHandlerID", &fooHandler)

	if err != nil {
		panic(err)
	}

	http.HandleFunc("/foo", WarpFuncPtr(&fooHandler))

	log.Fatal(http.ListenAndServe(":9988", nil))
}

func WarpFuncPtr(fn *func(w http.ResponseWriter, r *http.Request)) func(w http.ResponseWriter, r *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {
		(*fn)(w, r)
	}
}

Firstly create the Glean instance and load config from given file. And then use ReloadAndWatch to load fooHandler and begin to watch its changes. At last use WarpFuncPtr to wrap fooHandler as a HandleFunc.

Run go run main.go to start this server, use a browser to visit "http://locakhost:9988/foo" and you will see hello world

Change the config file plugin.json and replace "file": "plugins/plugin1/plugin1.so" with :

"file": "plugins/plugin2/plugin2.so",

Browser the prior location and you will see hello gp.