refeactor: remove command name check at each command level

There is no need to check the command name at this level because
we are garanteed to call from on the right command type in the code.

command/command.go

@@ -37,6 +37,13 @@ func NewCommand(cmdName string) Command {
 	}
 }
 
+// use that to fail fast when the command is not valid.
+var registeredCommands = map[string]struct{}{
+	"ping": {},
+	"set":  {},
+	"get":  {},
+}
+
 // GetCmdName gets a command name from a Frame Array.
 func GetCmdName(f *frame.Array) (string, error) {
 	if f.Size() < 1 {
@@ -47,5 +54,9 @@ func GetCmdName(f *frame.Array) (string, error) {
 	if !ok {
 		return "", gerror.ErrNotGcacheCmd
 	}
-	return strings.ToLower(cmdName.Value()), nil
+	cmdNameValue := strings.ToLower(cmdName.Value())
+	if _, ok = registeredCommands[cmdNameValue]; !ok {
+		return "", gerror.ErrInvalidCmdName
+	}
+	return cmdNameValue, nil
 }

command/get.go

@@ -37,11 +37,7 @@ func (c *Get) Apply(cache *db.Cache, dest *bufio.Writer) {
 }
 
 func (c *Get) FromFrame(f *frame.Array) error {
-	cmdName, err := GetCmdName(f)
-	if err != nil {
-		return err
-	}
-	if cmdName != "get" || f.Size() != 2 {
+	if f.Size() != 2 {
 		return gerror.ErrInvalidCmdArgs
 	}
 	c.key = f.Get(1).(*frame.BulkString).Value()

command/ping.go

@@ -38,12 +38,8 @@ func (c *Ping) Apply(_ *db.Cache, dest *bufio.Writer) {
 }
 
 func (c *Ping) FromFrame(f *frame.Array) error {
-	cmdName, err := GetCmdName(f)
-	if err != nil {
-		return err
-	}
 	switch {
-	case cmdName != "ping" || f.Size() > 2:
+	case f.Size() > 2:
 		return gerror.ErrInvalidPingCommand
 	case f.Size() == 1:
 		c.message = "PONG"

command/ping_test.go

@@ -5,6 +5,7 @@ import (
 	"bytes"
 	"github.com/stretchr/testify/assert"
 	"github.com/ynachi/gcache/frame"
+	"github.com/ynachi/gcache/gerror"
 	"log/slog"
 	"strings"
 	"testing"
@@ -53,9 +54,6 @@ func TestPing_FromFrame(t *testing.T) {
 	_ = pingWithMsg.Append(frame.NewBulkString("PING"))
 	_ = pingWithMsg.Append(frame.NewBulkString("Hello World"))
 
-	wrongCmd := frame.NewArray(1)
-	_ = wrongCmd.Append(frame.NewBulkString("PINg"))
-
 	pingTooManyArgs := frame.NewArray(3)
 	_ = pingTooManyArgs.Append(frame.NewBulkString("PING"))
 	_ = pingTooManyArgs.Append(frame.NewBulkString("Hello World"))
@@ -69,8 +67,7 @@ func TestPing_FromFrame(t *testing.T) {
 	}{
 		{name: "ValidSimplePing", frame: simplePING, want: "PONG", wantError: nil},
 		{name: "ValidPingWithMessage", frame: pingWithMsg, want: "Hello World", wantError: nil},
-		{name: "InvalidWrongCmdWord", frame: wrongCmd, want: "", wantError: ErrInvalidCmdName},
-		{name: "InvalidTooManyArgs", frame: pingTooManyArgs, want: "", wantError: ErrInvalidPingCommand},
+		{name: "InvalidTooManyArgs", frame: pingTooManyArgs, want: "", wantError: gerror.ErrInvalidPingCommand},
 	}
 
 	for _, tt := range tests {

command/set.go

@@ -31,11 +31,7 @@ func (c *Set) Apply(cache *db.Cache, dest *bufio.Writer) {
 
 // @TODO Minimal implementation for now, to fix
 func (c *Set) FromFrame(f *frame.Array) error {
-	cmdName, err := GetCmdName(f)
-	if err != nil {
-		return err
-	}
-	if cmdName != "set" || f.Size() != 3 {
+	if f.Size() != 3 {
 		return gerror.ErrInvalidCmdArgs
 	}
 	c.key = f.Get(1).(*frame.BulkString).Value()