[client] Refactor/iface pkg (#2646)

Refactor the flat code structure

client/iface/freebsd/iface.go

@@ -0,0 +1,108 @@
+package freebsd
+
+import (
+	"bufio"
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+type iface struct {
+	Name    string
+	MTU     int
+	Group   string
+	IPAddrs []string
+}
+
+func parseError(output []byte) error {
+	// TODO: implement without allocations
+	lines := string(output)
+
+	if strings.Contains(lines, "does not exist") {
+		return ErrDoesNotExist
+	}
+
+	return nil
+}
+
+func parseIfconfigOutput(output []byte) (*iface, error) {
+	// TODO: implement without allocations
+	lines := string(output)
+
+	scanner := bufio.NewScanner(strings.NewReader(lines))
+
+	var name, mtu, group string
+	var ips []string
+
+	for scanner.Scan() {
+		line := scanner.Text()
+
+		// If line contains ": flags", it's a line with interface information
+		if strings.Contains(line, ": flags") {
+			parts := strings.Fields(line)
+			if len(parts) < 4 {
+				return nil, fmt.Errorf("failed to parse line: %s", line)
+			}
+			name = strings.TrimSuffix(parts[0], ":")
+			if strings.Contains(line, "mtu") {
+				mtuIndex := 0
+				for i, part := range parts {
+					if part == "mtu" {
+						mtuIndex = i
+						break
+					}
+				}
+				mtu = parts[mtuIndex+1]
+			}
+		}
+
+		// If line contains "groups:", it's a line with interface group
+		if strings.Contains(line, "groups:") {
+			parts := strings.Fields(line)
+			if len(parts) < 2 {
+				return nil, fmt.Errorf("failed to parse line: %s", line)
+			}
+			group = parts[1]
+		}
+
+		// If line contains "inet ", it's a line with IP address
+		if strings.Contains(line, "inet ") {
+			parts := strings.Fields(line)
+			if len(parts) < 2 {
+				return nil, fmt.Errorf("failed to parse line: %s", line)
+			}
+			ips = append(ips, parts[1])
+		}
+	}
+
+	if name == "" {
+		return nil, fmt.Errorf("interface name not found in ifconfig output")
+	}
+
+	mtuInt, err := strconv.Atoi(mtu)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse MTU: %w", err)
+	}
+
+	return &iface{
+		Name:    name,
+		MTU:     mtuInt,
+		Group:   group,
+		IPAddrs: ips,
+	}, nil
+}
+
+func parseIFName(output []byte) (string, error) {
+	// TODO: implement without allocations
+	lines := strings.Split(string(output), "\n")
+	if len(lines) == 0 || lines[0] == "" {
+		return "", fmt.Errorf("no output returned")
+	}
+
+	fields := strings.Fields(lines[0])
+	if len(fields) > 1 {
+		return "", fmt.Errorf("invalid output")
+	}
+
+	return fields[0], nil
+}