Add Version method to NFT interface and implementation

Include `RunWithOutput` support in the command package and introduce version parsing logic, enabling retrieval of the nftables version and options.

nft.go

@@ -2,7 +2,10 @@ package nft
 
 import (
 	"errors"
+	"regexp"
+	"strings"
 
+	"git.kor-elf.net/kor-elf-shield/go-nftables-client/internal/chain"
 	"git.kor-elf.net/kor-elf-shield/go-nftables-client/internal/command"
 	"git.kor-elf.net/kor-elf-shield/go-nftables-client/internal/table"
 )
@@ -15,6 +18,12 @@ type NFT interface {
 	//    nft flush ruleset
 	Clear() error
 
+	// Version returns the version of nftables.
+	//
+	// This command is equivalent to:
+	//    nft -V
+	Version() (Version, error)
+
 	// Table returns an API for working with tables.
 	Table() table.API
 }
@@ -22,6 +31,7 @@ type NFT interface {
 type nft struct {
 	command command.NFT
 	table   table.API
+	chain   chain.API
 }
 
 // New Returns a client for working with nftables.
@@ -48,6 +58,7 @@ func NewWithPath(path string) (NFT, error) {
 	return &nft{
 		command: nftCommand,
 		table:   table.New(nftCommand),
+		chain:   chain.New(nftCommand),
 	}, nil
 }
 
@@ -56,6 +67,44 @@ func (n *nft) Clear() error {
 	return n.command.Run(args...)
 }
 
+func (n *nft) Version() (Version, error) {
+	args := []string{"-V"}
+	out, err := n.command.RunWithOutput(args...)
+	if err != nil {
+		return nil, err
+	}
+
+	vers := ""
+	opts := make(map[string]string)
+
+	lines := regexp.MustCompile("\r?\n").Split(strings.TrimSpace(string(out)), -1)
+	for index, line := range lines {
+		line = strings.TrimSpace(line)
+
+		if index == 0 {
+			vers = line
+			continue
+		}
+
+		values := strings.Split(line, ":")
+		if len(values) != 2 {
+			continue
+		}
+		name := strings.TrimSpace(values[0])
+		value := strings.TrimSpace(values[1])
+		opts[name] = value
+	}
+
+	return &version{
+		version: vers,
+		opts:    opts,
+	}, nil
+}
+
 func (n *nft) Table() table.API {
 	return n.table
 }
+
+func (n *nft) Chain() chain.API {
+	return n.chain
+}