crush/internal/shell/shell.go

// Package shell provides cross-platform shell execution capabilities.
//
// This package offers two main types:
// - Shell: A general-purpose shell executor for one-off or managed commands
// - PersistentShell: A singleton shell that maintains state across the application
//
// WINDOWS COMPATIBILITY:
// This implementation provides both POSIX shell emulation (mvdan.cc/sh/v3),
// even on Windows. Some caution has to be taken: commands should have forward
// slashes (/) as path separators to work, even on Windows.
package shell

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"os"
	"strings"
	"sync"

	"mvdan.cc/sh/moreinterp/coreutils"
	"mvdan.cc/sh/v3/expand"
	"mvdan.cc/sh/v3/interp"
	"mvdan.cc/sh/v3/syntax"
)

// ShellType represents the type of shell to use
type ShellType int

const (
	ShellTypePOSIX ShellType = iota
	ShellTypeCmd
	ShellTypePowerShell
)

// Logger interface for optional logging
type Logger interface {
	InfoPersist(msg string, keysAndValues ...any)
}

// noopLogger is a logger that does nothing
type noopLogger struct{}

func (noopLogger) InfoPersist(msg string, keysAndValues ...any) {}

// BlockFunc is a function that determines if a command should be blocked
type BlockFunc func(args []string) bool

// Shell provides cross-platform shell execution with optional state persistence
type Shell struct {
	env        []string
	cwd        string
	mu         sync.Mutex
	logger     Logger
	blockFuncs []BlockFunc
}

// Options for creating a new shell
type Options struct {
	WorkingDir string
	Env        []string
	Logger     Logger
	BlockFuncs []BlockFunc
}

// NewShell creates a new shell instance with the given options
func NewShell(opts *Options) *Shell {
	if opts == nil {
		opts = &Options{}
	}

	cwd := opts.WorkingDir
	if cwd == "" {
		cwd, _ = os.Getwd()
	}

	env := opts.Env
	if env == nil {
		env = os.Environ()
	}

	logger := opts.Logger
	if logger == nil {
		logger = noopLogger{}
	}

	return &Shell{
		cwd:        cwd,
		env:        env,
		logger:     logger,
		blockFuncs: opts.BlockFuncs,
	}
}

// Exec executes a command in the shell
func (s *Shell) Exec(ctx context.Context, command string) (string, string, error) {
	s.mu.Lock()
	defer s.mu.Unlock()

	return s.execPOSIX(ctx, command)
}

// GetWorkingDir returns the current working directory
func (s *Shell) GetWorkingDir() string {
	s.mu.Lock()
	defer s.mu.Unlock()
	return s.cwd
}

// SetWorkingDir sets the working directory
func (s *Shell) SetWorkingDir(dir string) error {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Verify the directory exists
	if _, err := os.Stat(dir); err != nil {
		return fmt.Errorf("directory does not exist: %w", err)
	}

	s.cwd = dir
	return nil
}

// GetEnv returns a copy of the environment variables
func (s *Shell) GetEnv() []string {
	s.mu.Lock()
	defer s.mu.Unlock()

	env := make([]string, len(s.env))
	copy(env, s.env)
	return env
}

// SetEnv sets an environment variable
func (s *Shell) SetEnv(key, value string) {
	s.mu.Lock()
	defer s.mu.Unlock()

	// Update or add the environment variable
	keyPrefix := key + "="
	for i, env := range s.env {
		if strings.HasPrefix(env, keyPrefix) {
			s.env[i] = keyPrefix + value
			return
		}
	}
	s.env = append(s.env, keyPrefix+value)
}

// SetBlockFuncs sets the command block functions for the shell
func (s *Shell) SetBlockFuncs(blockFuncs []BlockFunc) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.blockFuncs = blockFuncs
}

// CommandsBlocker creates a BlockFunc that blocks exact command matches
func CommandsBlocker(bannedCommands []string) BlockFunc {
	bannedSet := make(map[string]bool)
	for _, cmd := range bannedCommands {
		bannedSet[cmd] = true
	}

	return func(args []string) bool {
		if len(args) == 0 {
			return false
		}
		return bannedSet[args[0]]
	}
}

// ArgumentsBlocker creates a BlockFunc that blocks specific subcommands
func ArgumentsBlocker(blockedSubCommands [][]string) BlockFunc {
	return func(args []string) bool {
		for _, blocked := range blockedSubCommands {
			if len(args) >= len(blocked) {
				match := true
				for i, part := range blocked {
					if args[i] != part {
						match = false
						break
					}
				}
				if match {
					return true
				}
			}
		}
		return false
	}
}

func (s *Shell) blockHandler() func(next interp.ExecHandlerFunc) interp.ExecHandlerFunc {
	return func(next interp.ExecHandlerFunc) interp.ExecHandlerFunc {
		return func(ctx context.Context, args []string) error {
			if len(args) == 0 {
				return next(ctx, args)
			}

			for _, blockFunc := range s.blockFuncs {
				if blockFunc(args) {
					return fmt.Errorf("command is not allowed for security reasons: %s", strings.Join(args, " "))
				}
			}

			return next(ctx, args)
		}
	}
}

// execPOSIX executes commands using POSIX shell emulation (cross-platform)
func (s *Shell) execPOSIX(ctx context.Context, command string) (string, string, error) {
	line, err := syntax.NewParser().Parse(strings.NewReader(command), "")
	if err != nil {
		return "", "", fmt.Errorf("could not parse command: %w", err)
	}

	var stdout, stderr bytes.Buffer
	runner, err := interp.New(
		interp.StdIO(nil, &stdout, &stderr),
		interp.Interactive(false),
		interp.Env(expand.ListEnviron(s.env...)),
		interp.Dir(s.cwd),
		interp.ExecHandlers(s.blockHandler(), coreutils.ExecHandler),
	)
	if err != nil {
		return "", "", fmt.Errorf("could not run command: %w", err)
	}

	err = runner.Run(ctx, line)
	s.cwd = runner.Dir
	s.env = []string{}
	for name, vr := range runner.Vars {
		s.env = append(s.env, fmt.Sprintf("%s=%s", name, vr.Str))
	}
	s.logger.InfoPersist("POSIX command finished", "command", command, "err", err)
	return stdout.String(), stderr.String(), err
}

// IsInterrupt checks if an error is due to interruption
func IsInterrupt(err error) bool {
	return errors.Is(err, context.Canceled) ||
		errors.Is(err, context.DeadlineExceeded)
}

// ExitCode extracts the exit code from an error
func ExitCode(err error) int {
	if err == nil {
		return 0
	}
	var exitErr interp.ExitStatus
	if errors.As(err, &exitErr) {
		return int(exitErr)
	}
	return 1
}