add test boilerplate for sharding client

Former-commit-id: 7cbd81db9421e1517ad92829a2dbbdfcf5f38699 [formerly 76607161435699e18a970c82f9838d20e94f04d7]
Former-commit-id: f6db97246aa70eda35e59a2a05fa55316289bd76

cmd/geth/shardingcmd.go

@@ -1,7 +1,6 @@
 package main
 
 import (
-	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/sharding"
 
 	"github.com/ethereum/go-ethereum/cmd/utils"
@@ -20,7 +19,6 @@ var (
 )
 
 func shardingClient(ctx *cli.Context) error {
-	log.Info("hello world!")
 	c := sharding.MakeShardingClient(ctx)
 	if err := c.Start(); err != nil {
 		return err

sharding/client.go

@@ -1,29 +1,58 @@
 package sharding
 
 import (
+	"github.com/ethereum/go-ethereum/cmd/utils"
 	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/node"
+	"github.com/ethereum/go-ethereum/rpc"
 	cli "gopkg.in/urfave/cli.v1"
 )
 
+const (
+	// TODO: Can this be referenced from main.clientIdentifier?
+	clientIdentifier = "geth" // Client identifier to advertise over the network
+)
+
 type Client struct {
+	endpoint string
+	client   *rpc.Client
 }
 
 func MakeShardingClient(ctx *cli.Context) *Client {
-	// TODO: Setup client
-	return &Client{}
+	endpoint := ""
+	if ctx.GlobalIsSet(utils.DataDirFlag.Name) {
+		endpoint = ctx.GlobalString(utils.DataDirFlag.Name)
+	}
+
+	return &Client{
+		endpoint: endpoint,
+	}
 }
 
 func (c *Client) Start() error {
 	log.Info("Starting sharding client")
-	// TODO: Dial to RPC
-	// TODO: Verify VMC
+	rpcClient, err := dialRPC(c.endpoint)
+	if err != nil {
+		return err
+	}
+	c.client = rpcClient
+	defer c.client.Close()
 	if err := c.verifyVMC(); err != nil {
 		return err
 	}
 
+	// TODO: Wait to be selected?
+
 	return nil
 }
 
 func (c *Client) Wait() {
 	// TODO: Blocking lock
 }
+
+func dialRPC(endpoint string) (*rpc.Client, error) {
+	if endpoint == "" {
+		endpoint = node.DefaultIPCEndpoint(clientIdentifier)
+	}
+	return rpc.Dial(endpoint)
+}

sharding/client_test.go

@@ -0,0 +1,54 @@
+package sharding
+
+import (
+	"flag"
+	"fmt"
+	"math/rand"
+	"os"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/cmd/utils"
+	"github.com/ethereum/go-ethereum/rpc"
+	cli "gopkg.in/urfave/cli.v1"
+)
+
+func randomEndpoint() string {
+	return fmt.Sprintf("/tmp/go-ethereum-test-ipc-%d-%d", os.Getpid(), rand.Int63())
+}
+
+func newTestServer(endpoint string) (*rpc.Server, error) {
+	server := rpc.NewServer()
+
+	l, err := rpc.CreateIPCListener(endpoint)
+	if err != nil {
+		return nil, err
+	}
+	go server.ServeListener(l)
+
+	return server, nil
+}
+
+func createContext() *cli.Context {
+	set := flag.NewFlagSet("test", 0)
+	set.String(utils.DataDirFlag.Name, "", "")
+	return cli.NewContext(nil, set, nil)
+}
+
+func TestStart(t *testing.T) {
+	endpoint := randomEndpoint()
+	server, err := newTestServer(endpoint)
+	if err != nil {
+		t.Fatalf("Failed to create a test server: %v", err)
+	}
+	defer server.Stop()
+
+	ctx := createContext()
+	if err := ctx.GlobalSet(utils.DataDirFlag.Name, endpoint); err != nil {
+		t.Fatalf("Failed to set global variable for flag %s. Error: %v", utils.DataDirFlag.Name, err)
+	}
+
+	c := MakeShardingClient(ctx)
+	if err := c.Start(); err != nil {
+		t.Errorf("Failed to start server: %v", err)
+	}
+}