Convert errors to serializable errors

Plain errors cannot be serialized over gRPC without some gob work so
this change makes use of the internal BasicError type from go-plugin to
send the information back to server.

Upstream bug:

golang/go#23340

app/main.go

@@ -8,7 +8,7 @@ import (
 	"os/exec"
 	"path/filepath"
 
-	"github.com/hashicorp/go-plugin"
+	go_plugin "github.com/hashicorp/go-plugin"
 
 	app_plugin "github.com/sgnn7/golang-grpc-plugin-test/app/plugin"
 	tcp_connector "github.com/sgnn7/golang-grpc-plugin-test/app/plugin/connector/tcp"
@@ -27,7 +27,7 @@ func (manager *PluginManager) StartPlugin(pluginName string) error {
 
 	log.Printf("Starting plugin: %s", pluginFile)
 
-	client := plugin.NewClient(&plugin.ClientConfig{
+	client := go_plugin.NewClient(&go_plugin.ClientConfig{
 		Cmd:        exec.Command(pluginFile),
 		Managed:    true,
 		SyncStdout: os.Stdout,
@@ -57,7 +57,7 @@ func (manager *PluginManager) StartPlugin(pluginName string) error {
 		for {
 			log.Println()
 			log.Printf("RCP call to plugin response: %v",
-				tcpConnectorObj.Connect("tcp://localhost:8080"))
+				tcpConnectorObj.Connect("localhost:8080"))
 			time.Sleep(1000 * time.Millisecond)
 		}
 	}()

app/plugin/connector/tcp/goplugin-client.go

@@ -22,10 +22,10 @@ func (tcpConnectorPlugin *TCPConnector) Client(pluginBroker *plugin.MuxBroker,
 	}, nil
 }
 
-func (tcpConnectorClient *tcpConnectorClient) Connect(address string) error {
+func (tcpConnectorClient *tcpConnectorClient) Connect(address string) plugin.BasicError {
 	log.Printf("In: Client Connect: %s", address)
 
-	var resp_err error
+	var resp_err plugin.BasicError
 
 	err := tcpConnectorClient.Client.Call("Plugin.Connect", &address, &resp_err)
 	if err != nil {

app/plugin/connector/tcp/goplugin-server.go

@@ -23,7 +23,7 @@ func (tcpConnectorPlugin *TCPConnector) Server(pluginBroker *plugin.MuxBroker) (
 	}, nil
 }
 
-func (tcpConnectorPlugin *tcpConnectorServer) Connect(address string, result *error) error {
+func (tcpConnectorPlugin *tcpConnectorServer) Connect(address string, result *plugin.BasicError) error {
 	log.Printf("In: Server Connect: %s", address)
 	*result = tcpConnectorPlugin.ITCPConnector.Connect(address)
 	log.Printf("In: Server Reply Response: %v", *result)

app/plugin/connector/tcp/tcp.go

@@ -1,9 +1,13 @@
 package tcp
 
+import (
+	"github.com/hashicorp/go-plugin"
+)
+
 const InterfaceName = "TCPConnector"
 
 type ITCPConnector interface {
-	Connect(address string) error
+	Connect(address string) plugin.BasicError
 }
 
 type TCPConnectorFunc func() ITCPConnector

plugin/main.go

@@ -2,9 +2,11 @@ package main
 
 import (
 	"log"
+	"net"
 	"time"
 
-	"github.com/sgnn7/golang-grpc-plugin-test/app/plugin"
+	go_plugin "github.com/hashicorp/go-plugin"
+	app_plugin "github.com/sgnn7/golang-grpc-plugin-test/app/plugin"
 	tcp_connector "github.com/sgnn7/golang-grpc-plugin-test/app/plugin/connector/tcp"
 )
 
@@ -18,18 +20,38 @@ func TCPConnector() tcp_connector.ITCPConnector {
 	return &tcpConnectorImpl{}
 }
 
-func (p *tcpConnectorImpl) Connect(address string) error {
+func (p *tcpConnectorImpl) Connect(address string) go_plugin.BasicError {
 	log.Printf("Plugin Connect: %s", address)
-	return nil
+
+	log.Println("Starting plugin client...")
+	connection, err := net.Dial("tcp", address)
+	if err != nil {
+		log.Printf("Plugin Connect Dial Error: %v", err)
+		return *go_plugin.NewBasicError(err)
+	}
+
+	if err = connection.Close(); err != nil {
+		log.Printf("Plugin Connect Close Error: %v", err)
+		return *go_plugin.NewBasicError(err)
+	}
+
+	if _, err = connection.Write([]byte("foobar")); err != nil {
+		log.Printf("Plugin Connect Write Error: %v", err)
+		return *go_plugin.NewBasicError(err)
+	}
+
+	log.Printf("Plugin Connect OK!")
+
+	return *go_plugin.NewBasicError(nil)
 }
 
 func main() {
-	pluginOpts := &plugin.PluginOpts{
+	pluginOpts := &app_plugin.PluginOpts{
 		TCPConnector: TCPConnector,
 		RunAsPlugin:  true,
 	}
 
-	plugin.StartPlugin(pluginOpts, make(chan bool))
+	app_plugin.StartPlugin(pluginOpts, make(chan bool))
 
 	//	tcpConnectorPlugin := TCPConnector()
 	for {