rs2322tcp/internal/client/virtual_port_linux.go

//go:build linux

/*
 * ============================================================================
 * Projekt.....: rs2322tcp
 * Datei.......: internal/client/virtual_port_linux.go
 * Copyright (C) 2026 Dieter Lang
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 * Beschreibung:
 * Linux-spezifische Verwaltung der internen Symlinks für virtuelle
 * rs2322tcp-Seriellschnittstellen.
 *
 * Der öffentliche Gerätename /dev/ttyUSBxxx wird bei der Installation
 * vorbereitet. Der Client verwaltet ausschließlich den benutzerbezogenen
 * Link unter ~/.rs2322tcp/virtual/.
 * ============================================================================
 */
package client

import (
	"fmt"
	"os"
	"path/filepath"

	"git.lang-dieter.de/rs2322tcp/internal/config"
)

const (
	virtualDirectoryName = ".rs2322tcp/virtual"
)

// virtualPortDirectory returns the directory in the current user's home
// directory used for the internal virtual-port links.
func virtualPortDirectory() (string, error) {
	home, err := os.UserHomeDir()
	if err != nil {
		return "", fmt.Errorf("get user home directory: %w", err)
	}

	return filepath.Join(home, virtualDirectoryName), nil
}

// virtualPortLinkPath returns the path of the internal link for a virtual
// serial port.
func virtualPortLinkPath(portPath string) (string, error) {
	directory, err := virtualPortDirectory()
	if err != nil {
		return "", err
	}

	return filepath.Join(directory, filepath.Base(portPath)), nil
}

// ensureVirtualPortDirectory creates the internal virtual-port directory
// if it does not already exist.
func ensureVirtualPortDirectory() error {
	directory, err := virtualPortDirectory()
	if err != nil {
		return err
	}

	if err := os.MkdirAll(directory, 0755); err != nil {
		return fmt.Errorf(
			"create virtual port directory %q: %w",
			directory,
			err,
		)
	}

	return nil
}

// setVirtualPortLink creates or replaces the internal link for a virtual
// port.
//
// The link itself is located below ~/.rs2322tcp/virtual/ and points to the
// current PTY, for example /dev/pts/2.
func setVirtualPortLink(portPath string, target string) error {
	if portPath == "" {
		return fmt.Errorf("virtual port path is empty")
	}

	if target == "" {
		return fmt.Errorf("virtual port target is empty")
	}

	if err := ensureVirtualPortDirectory(); err != nil {
		return err
	}

	linkPath, err := virtualPortLinkPath(portPath)
	if err != nil {
		return err
	}

	// Remove an existing link. The installation-owned outer /dev/ttyUSBxxx
	// link is deliberately never touched here.
	if err := os.Remove(linkPath); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf(
			"remove existing virtual port link %q: %w",
			linkPath,
			err,
		)
	}

	if err := os.Symlink(target, linkPath); err != nil {
		return fmt.Errorf(
			"create virtual port link %q -> %q: %w",
			linkPath,
			target,
			err,
		)
	}

	return nil
}

// removeVirtualPortLink removes the internal link for a virtual port.
//
// The public /dev/ttyUSBxxx link is never modified.
func removeVirtualPortLink(portPath string) error {
	if portPath == "" {
		return fmt.Errorf("virtual port path is empty")
	}

	linkPath, err := virtualPortLinkPath(portPath)
	if err != nil {
		return err
	}

	if err := os.Remove(linkPath); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf(
			"remove existing virtual port link %q: %w",
			linkPath,
			err,
		)
	}

	return nil
}

// existingVirtualPortLinks returns all public virtual-port paths that
// currently exist as symbolic links.
//
// Only ports inside the configured virtual-port range are considered.
// The public /dev/ttyUSBxxx links are only inspected; they are never
// created, changed, or removed by this function.
//
// This check only requires read access and therefore does not require
// root privileges.
func existingVirtualPortLinks(
	cfg config.VirtualPortRangeConfig,
) ([]string, error) {
	return existingVirtualPortLinksInDirectory(
		cfg,
		"/dev",
	)
}

// existingVirtualPortLinksInDirectory returns all virtual-port paths in
// directory that currently exist as symbolic links.
//
// This helper is deliberately separated from existingVirtualPortLinks so
// the filesystem inspection can be tested without modifying /dev.
func existingVirtualPortLinksInDirectory(
	cfg config.VirtualPortRangeConfig,
	directory string,
) ([]string, error) {
	if directory == "" {
		return nil, fmt.Errorf("virtual port directory is empty")
	}

	manager := NewVirtualPortManager(cfg)
	if manager == nil {
		return nil, fmt.Errorf("virtual port manager is nil")
	}

	links := make([]string, 0)

	for number := cfg.First; number <= cfg.Last; number++ {
		portName := filepath.Base(
			manager.PortPath(number),
		)
		portPath := filepath.Join(directory, portName)

		info, err := os.Lstat(portPath)
		if err != nil {
			if os.IsNotExist(err) {
				continue
			}

			return nil, fmt.Errorf(
				"inspect virtual port %q: %w",
				portPath,
				err,
			)
		}

		if info.Mode()&os.ModeSymlink == 0 {
			continue
		}

		links = append(
			links,
			filepath.Join(directory, portName),
		)
	}

	return links, nil
}