connect: add eval functionality to the module

The patch adds `eval` functionality to the connect module.
Now, if code has been passed in by a command, it will be
executed on the instance and the result (in YAML format) will
be returned to `stdout`.

Part of #15

cli/cmd/connect.go

@@ -1,6 +1,7 @@
 package cmd
 
 import (
+	"fmt"
 	"syscall"
 
 	"github.com/apex/log"
@@ -37,15 +38,30 @@ func NewConnectCmd() *cobra.Command {
 
 // internalConnectModule is a default connect module.
 func internalConnectModule(cmdCtx *cmdcontext.CmdCtx, args []string) error {
-	// Fill CmdCtx.
+	argsLen := len(args)
+	if argsLen < 1 {
+		return fmt.Errorf("Incorrect combination of command parameters")
+	}
+
 	cmdCtx.Connect.Username = connectUser
 	cmdCtx.Connect.Password = connectPassword
 
-	if terminal.IsTerminal(syscall.Stdin) {
-		log.Info("Connecting to the instance...")
-	}
-	if err := connect.Connect(cmdCtx, args); err != nil {
-		return err
+	if argsLen == 1 {
+		if terminal.IsTerminal(syscall.Stdin) {
+			log.Info("Connecting to the instance...")
+		}
+		if err := connect.Connect(cmdCtx, args); err != nil {
+			return err
+		}
+	} else if argsLen == 2 {
+		res, err := connect.Eval(cmdCtx, args)
+		if err != nil {
+			return err
+		}
+		// "Println" is used instead of "log..." to print the result without any decoration.
+		fmt.Println(string(res))
+	} else {
+		return fmt.Errorf("Incorrect combination of command parameters")
 	}
 
 	return nil

cli/connect/connect.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/tarantool/tt/cli/cmdcontext"
 	"github.com/tarantool/tt/cli/connector"
+	"gopkg.in/yaml.v2"
 )
 
 const (
@@ -32,6 +33,38 @@ func Connect(cmdCtx *cmdcontext.CmdCtx, args []string) error {
 	return nil
 }
 
+// Eval executes the command on the remote instance (according to args).
+func Eval(cmdCtx *cmdcontext.CmdCtx, args []string) ([]byte, error) {
+	// Parse the arguments.
+	connString := args[0]
+	connOpts := getConnOpts(connString, cmdCtx)
+	command := args[1]
+
+	// Connecting to the instance.
+	conn, err := connector.Connect(connOpts.Address, connOpts.Username, connOpts.Password)
+	if err != nil {
+		return nil, fmt.Errorf("Unable to establish connection: %s", err)
+	}
+
+	// Execution of the command.
+	req := connector.EvalReq(evalFuncBody, command)
+	res, err := conn.Exec(req)
+	if err != nil {
+		return nil, err
+	}
+
+	// Check that the result is encoded in YAML and convert it to bytes,
+	// since the ""gopkg.in/yaml.v2" library handles YAML as an array
+	// of bytes.
+	resYAML := []byte((res[0]).(string))
+	var checkMock interface{}
+	if err = yaml.Unmarshal(resYAML, &checkMock); err != nil {
+		return nil, err
+	}
+
+	return resYAML, nil
+}
+
 // runConsole run a new console.
 func runConsole(connOpts *connector.ConnOpts, title string) error {
 	console, err := NewConsole(connOpts, title)

cli/connector/connector.go

@@ -85,6 +85,13 @@ func (conn *Conn) Exec(req *Request) ([]interface{}, error) {
 	return req.execFunc(conn)
 }
 
+// Eval executes a command.
+func (conn *Conn) Eval(command string) ([]interface{}, error) {
+	evalFuncBody := "return require('console').eval(...)\n"
+	req := EvalReq(evalFuncBody, command)
+	return conn.Exec(req)
+}
+
 // ExecTyped executes an operation and returns the typed result.
 func (conn *Conn) ExecTyped(req *Request, resData interface{}) error {
 	return req.execTypedFunc(conn, resData)