pool: get instance status from WatchOnce request

Starting from Tarantool version >= 3.0.0 `WatchOnce` requset is
supported. So we can get instance status using this request instead
of calling `box.info`.

This way user can add instances to the pool without the `execute` role.

Closes #380

CHANGELOG.md

@@ -12,6 +12,9 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
 
 ### Changed
 
+- `execute` role is no longer required for adding instances to the pool for
+  Tarantool version >= 3.0.0 (#380)
+
 ### Fixed
 
 - `ConnectionPool.Remove()` does not notify a `ConnectionHandler` after

pool/config.lua

@@ -9,6 +9,9 @@ box.once("init", function()
     box.schema.user.create('test', { password = 'test' })
     box.schema.user.grant('test', 'read,write,execute', 'universe')
 
+    box.schema.user.create('testNoExecute', { password = 'test' })
+    box.schema.user.grant('testNoExecute', 'read,write', 'universe')
+
     local s = box.schema.space.create('testPool', {
         id = 520,
         if_not_exists = true,

pool/connection_pool.go

@@ -1017,7 +1017,20 @@ func (p *ConnectionPool) DoInstance(req tarantool.Request, name string) *taranto
 //
 
 func (p *ConnectionPool) getConnectionRole(conn *tarantool.Connection) (Role, error) {
-	data, err := conn.Do(tarantool.NewCallRequest("box.info")).Get()
+	var (
+		roFieldName string
+		data        []interface{}
+		err         error
+	)
+
+	if isFeatureInSlice(iproto.IPROTO_FEATURE_WATCH_ONCE, conn.ProtocolInfo().Features) {
+		roFieldName = "is_ro"
+		data, err = conn.Do(tarantool.NewWatchOnceRequest("box.status")).Get()
+	} else {
+		roFieldName = "ro"
+		data, err = conn.Do(tarantool.NewCallRequest("box.info")).Get()
+	}
+
 	if err != nil {
 		return UnknownRole, err
 	}
@@ -1033,7 +1046,7 @@ func (p *ConnectionPool) getConnectionRole(conn *tarantool.Connection) (Role, er
 		return UnknownRole, ErrIncorrectStatus
 	}
 
-	replicaRole, ok := data[0].(map[interface{}]interface{})["ro"]
+	replicaRole, ok := data[0].(map[interface{}]interface{})[roFieldName]
 	if !ok {
 		return UnknownRole, ErrIncorrectResponse
 	}

pool/connection_pool_test.go

@@ -1,6 +1,7 @@
 package pool_test
 
 import (
+	"bytes"
 	"context"
 	"fmt"
 	"log"
@@ -22,6 +23,7 @@ import (
 )
 
 var user = "test"
+var userNoExecute = "testNoExecute"
 var pass = "test"
 var spaceNo = uint32(520)
 var spaceName = "testPool"
@@ -68,6 +70,18 @@ func makeInstance(server string, opts tarantool.Opts) pool.Instance {
 	}
 }
 
+func makeNoExecuteInstance(server string, opts tarantool.Opts) pool.Instance {
+	return pool.Instance{
+		Name: server,
+		Dialer: tarantool.NetDialer{
+			Address:  server,
+			User:     userNoExecute,
+			Password: pass,
+		},
+		Opts: opts,
+	}
+}
+
 func makeInstances(servers []string, opts tarantool.Opts) []pool.Instance {
 	var instances []pool.Instance
 	for _, server := range servers {
@@ -130,6 +144,76 @@ func TestConnSuccessfully(t *testing.T) {
 	require.Nil(t, err)
 }
 
+func TestConn_NoExecuteRole_Supported(t *testing.T) {
+	test_helpers.SkipIfWatchOnceUnsupported(t)
+
+	healthyServ := servers[0]
+
+	ctx, cancel := test_helpers.GetPoolConnectContext()
+	defer cancel()
+	connPool, err := pool.Connect(ctx,
+		[]pool.Instance{makeNoExecuteInstance(healthyServ, connOpts)})
+	require.Nilf(t, err, "failed to connect")
+	require.NotNilf(t, connPool, "conn is nil after Connect")
+
+	defer connPool.Close()
+
+	args := test_helpers.CheckStatusesArgs{
+		ConnPool:           connPool,
+		Mode:               pool.ANY,
+		Servers:            []string{healthyServ},
+		ExpectedPoolStatus: true,
+		ExpectedStatuses: map[string]bool{
+			healthyServ: true,
+		},
+	}
+
+	err = test_helpers.CheckPoolStatuses(args)
+	require.Nil(t, err)
+}
+
+func TestConn_NoExecuteRole_Unsupported(t *testing.T) {
+	watchOnceUnsupported, err := test_helpers.IsTarantoolVersionLess(3, 0, 0)
+	require.NoError(t, err)
+	if !watchOnceUnsupported {
+		t.Skip("Skipping test for Tarantool with watch once support")
+	}
+
+	var buf bytes.Buffer
+	log.SetOutput(&buf)
+	defer func() {
+		log.SetOutput(os.Stderr)
+	}()
+
+	healthyServ := servers[0]
+
+	ctx, cancel := test_helpers.GetPoolConnectContext()
+	defer cancel()
+	connPool, err := pool.Connect(ctx,
+		[]pool.Instance{makeNoExecuteInstance(healthyServ, connOpts)})
+	require.Nilf(t, err, "failed to connect")
+	require.NotNilf(t, connPool, "conn is nil after Connect")
+
+	defer connPool.Close()
+
+	require.Contains(t, buf.String(),
+		fmt.Sprintf("connect to %s failed: Execute access to function "+
+			"'box.info' is denied for user '%s'", servers[0], userNoExecute))
+
+	args := test_helpers.CheckStatusesArgs{
+		ConnPool:           connPool,
+		Mode:               pool.ANY,
+		Servers:            []string{healthyServ},
+		ExpectedPoolStatus: false,
+		ExpectedStatuses: map[string]bool{
+			healthyServ: false,
+		},
+	}
+
+	err = test_helpers.CheckPoolStatuses(args)
+	require.Nil(t, err)
+}
+
 func TestConnect_empty(t *testing.T) {
 	cases := []struct {
 		Name      string