一個golang項目筆記 （二） 動態載入庫

這個項目需要用到動態連結程式庫技術， 主程式動態載入一些功能模組，這樣在擴充功能時，無須修改主程式，只需要新增功能模組動態調用就可以了。 研究了一下golang官方支援的plugin功能，發現有幾點不足。 

     1.官方plugin功能本質上是用cgo實現的，編譯一個so檔案，然後再調用

     2. 只支援linux， 不支援windows

     3.  plugin模組panic時， 主程式也會panic, 無法做到隔離。

   基於上述原因，我開始另外尋找合適的第三方支援。後來發現這樣一個開源庫，https://github.com/hashicorp/go-plugin , 感覺符合我的需求。它基於net/rpc ，grpc實現，主程式和plugin程式是兩個qtj獨立進程，可以通過主程式調用plugin進程啟動，也可以附加進程的方式。通過本網通訊，達到類似動態連結程式庫調用的效果。 

官方樣本如下：

plugin:  

package mainimport ("os""github.com/hashicorp/go-hclog""github.com/hashicorp/go-plugin""github.com/hashicorp/go-plugin/examples/basic/commons")// Here is a real implementation of Greetertype GreeterHello struct {logger hclog.Logger}func (g *GreeterHello) Greet() string {g.logger.Debug("message from GreeterHello.Greet")return "Hello!"}// handshakeConfigs are used to just do a basic handshake between// a plugin and host. If the handshake fails, a user friendly error is shown.// This prevents users from executing bad plugins or executing a plugin// directory. It is a UX feature, not a security feature.var handshakeConfig = plugin.HandshakeConfig{ProtocolVersion:  1,MagicCookieKey:   "BASIC_PLUGIN",MagicCookieValue: "hello",}func main() {logger := hclog.New(&hclog.LoggerOptions{Level:      hclog.Trace,Output:     os.Stderr,JSONFormat: true,})greeter := &GreeterHello{logger: logger,}// pluginMap is the map of plugins we can dispense.var pluginMap = map[string]plugin.Plugin{"greeter": &example.GreeterPlugin{Impl: greeter},}logger.Debug("message from plugin", "foo", "bar")plugin.Serve(&plugin.ServeConfig{HandshakeConfig: handshakeConfig,Plugins:         pluginMap,})}

　　主程式 （調用方）：

package mainimport ("fmt""log""os""os/exec"hclog "github.com/hashicorp/go-hclog""github.com/hashicorp/go-plugin""github.com/hashicorp/go-plugin/examples/basic/commons")func main() {// Create an hclog.Loggerlogger := hclog.New(&hclog.LoggerOptions{Name:   "plugin",Output: os.Stdout,Level:  hclog.Debug,})// We're a host! Start by launching the plugin process.client := plugin.NewClient(&plugin.ClientConfig{HandshakeConfig: handshakeConfig,Plugins:         pluginMap,Cmd:             exec.Command("./plugin/greeter"),Logger:          logger,})defer client.Kill()// Connect via RPCrpcClient, err := client.Client()if err != nil {log.Fatal(err)}// Request the pluginraw, err := rpcClient.Dispense("greeter")if err != nil {log.Fatal(err)}// We should have a Greeter now! This feels like a normal interface// implementation but is in fact over an RPC connection.greeter := raw.(example.Greeter)fmt.Println(greeter.Greet())}// handshakeConfigs are used to just do a basic handshake between// a plugin and host. If the handshake fails, a user friendly error is shown.// This prevents users from executing bad plugins or executing a plugin// directory. It is a UX feature, not a security feature.var handshakeConfig = plugin.HandshakeConfig{ProtocolVersion:  1,MagicCookieKey:   "BASIC_PLUGIN",MagicCookieValue: "hello",}// pluginMap is the map of plugins we can dispense.var pluginMap = map[string]plugin.Plugin{"greeter": &example.GreeterPlugin{},}