cmd/geth: make attach tests more reliable

This makes the test wait for the endpoint to come up by polling
it instead of waiting for two seconds.

cmd/geth/consolecmd_test.go

@@ -87,7 +87,7 @@ func TestIPCAttachWelcome(t *testing.T) {
 		"--port", "0", "--maxpeers", "0", "--nodiscover", "--nat", "none",
 		"--etherbase", coinbase, "--shh", "--ipcpath", ipc)
 
-	time.Sleep(2 * time.Second) // Simple way to wait for the RPC endpoint to open
+	waitForEndpoint(t, ipc, 3*time.Second)
 	testAttachWelcome(t, geth, "ipc:"+ipc, ipcAPIs)
 
 	geth.Interrupt()
@@ -101,8 +101,9 @@ func TestHTTPAttachWelcome(t *testing.T) {
 		"--port", "0", "--maxpeers", "0", "--nodiscover", "--nat", "none",
 		"--etherbase", coinbase, "--rpc", "--rpcport", port)
 
-	time.Sleep(2 * time.Second) // Simple way to wait for the RPC endpoint to open
+	endpoint := "http://127.0.0.1:" + port
-	testAttachWelcome(t, geth, "http://localhost:"+port, httpAPIs)
+	waitForEndpoint(t, endpoint, 3*time.Second)
+	testAttachWelcome(t, geth, endpoint, httpAPIs)
 
 	geth.Interrupt()
 	geth.ExpectExit()
@@ -116,8 +117,9 @@ func TestWSAttachWelcome(t *testing.T) {
 		"--port", "0", "--maxpeers", "0", "--nodiscover", "--nat", "none",
 		"--etherbase", coinbase, "--ws", "--wsport", port)
 
-	time.Sleep(2 * time.Second) // Simple way to wait for the RPC endpoint to open
+	endpoint := "ws://127.0.0.1:" + port
-	testAttachWelcome(t, geth, "ws://localhost:"+port, httpAPIs)
+	waitForEndpoint(t, endpoint, 3*time.Second)
+	testAttachWelcome(t, geth, endpoint, httpAPIs)
 
 	geth.Interrupt()
 	geth.ExpectExit()

cmd/geth/run_test.go

@@ -17,13 +17,16 @@
 package main
 
 import (
+	"context"
 	"fmt"
 	"io/ioutil"
 	"os"
 	"testing"
+	"time"
 
 	"github.com/docker/docker/pkg/reexec"
 	"github.com/ethereum/go-ethereum/internal/cmdtest"
+	"github.com/ethereum/go-ethereum/rpc"
 )
 
 func tmpdir(t *testing.T) string {
@@ -96,3 +99,28 @@ func runGeth(t *testing.T, args ...string) *testgeth {
 
 	return tt
 }
+
+// waitForEndpoint attempts to connect to an RPC endpoint until it succeeds.
+func waitForEndpoint(t *testing.T, endpoint string, timeout time.Duration) {
+	probe := func() bool {
+		ctx, cancel := context.WithTimeout(context.Background(), timeout)
+		defer cancel()
+		c, err := rpc.DialContext(ctx, endpoint)
+		if c != nil {
+			_, err = c.SupportedModules()
+			c.Close()
+		}
+		return err == nil
+	}
+
+	start := time.Now()
+	for {
+		if probe() {
+			return
+		}
+		if time.Since(start) > timeout {
+			t.Fatal("endpoint", endpoint, "did not open within", timeout)
+		}
+		time.Sleep(200 * time.Millisecond)
+	}
+}