Repository: amenzhinsky/go-memexec
Branch: main
Commit: d27e26edbf40
Files: 13
Total size: 24.8 KB

Directory structure:
gitextract_rtw5rwam/

├── .github/
│   └── workflows/
│       └── test.yml
├── LICENSE
├── README.md
├── cmd/
│   └── memexec-gen/
│       └── main.go
├── go.mod
├── go.sum
├── memexec.go
├── memexec_all.go
├── memexec_linux.go
├── memexec_linux_test.go
├── memexec_test.go
└── testdata/
    ├── .gitignore
    └── main.go

================================================
FILE CONTENTS
================================================

================================================
FILE: .github/workflows/test.yml
================================================
name: Test and Lint
on:
  push:
    branches:
      - main
  pull_request:
    branches:
      - main

jobs:
  test:
    name: Test
    strategy:
      matrix:
        platform:
          - ubuntu-latest
          - macos-latest
          - windows-latest
    runs-on: ${{ matrix.platform }}
    steps:
      - uses: actions/checkout@v3
      - uses: actions/setup-go@v3
        with:
          go-version: 1.19
      - name: Run Tests
        run: go test -v ./...

  lint:
    name: Lint
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: actions/setup-go@v3
        with:
          go-version: 1.19
      - name: Run golangci-lint
        uses: golangci/golangci-lint-action@v3
        with:
          version: v1.52.0
          args: --enable=gofumpt,goimports,whitespace,gocritic,exportloopref,unconvert,prealloc


================================================
FILE: LICENSE
================================================
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================================================
FILE: README.md
================================================
# go-memexec

Small library that executes binaries from the memory.

## Usage

## Static Binary

Running static binaries is quite simple, it's only needed to embed it into the app and pass its content to `memexec.New`:

```go
import (
	_ "embed"
	
	"github.com/amenzhinsky/go-memexec"
)

// go:embed path-to-binary
var mybinary []byte

exe, err := memexec.New(mybinary)
if err != nil {
	return err
}
defer exe.Close()

cmd := exe.Command(argv...)
cmd.Output() // cmd is a `*exec.Cmd` from the standard library
```

## Dynamic Binary (Linux only)

With dynamic linked binaries things get more complicated, it's needed to embed all dependencies along with the executable.

At the runtime deps are copied to a temp dir and executable receives the corresponding `LD_LIBRARY_PATH` that forces the dynamic linker to use the copied libraries.

The dynamic linker must be the same on both building and running machines since it's not included in the resulting binary (there's no interoperability between musl and GNU systems).

The following script helps generating packages, say `python3`:

```sh
go install github.com/amenzhinsky/go-memexec/cmd/memexec-gen@latest
PATH=$(go env GOPATH)/bin:$PATH memexec-gen /usr/bin/python3
```

It produces `python3` directory with binaries are to embed and `gen.go` file, that is a go package:

```go
import "mypackagename/python3"

exe, err := python3.New()
if err != nil {
	return err
}
defer exe.Close()

b, err := exe.Command("-c", "print('Hello World')").CombinedOutput()
if err != nil {
	return err
}
```


================================================
FILE: cmd/memexec-gen/main.go
================================================
//go:build linux

package main

import (
	"debug/elf"
	"flag"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"runtime"
	"strings"
)

var (
	destFlag    string
	packageFlag string
)

func main() {
	flag.Usage = func() {
		fmt.Fprint(os.Stderr, `Usage: memexec-gen PATH

Environment variables:
  LD_LIBRARY_PATH
  	list of directories where to search libraries, see 'man 7 ld.so'

Options:
`)
		flag.PrintDefaults()
	}
	flag.StringVar(&destFlag, "dest", "",
		"`path` where binaries and go file are written to, defaults to PATH basename",
	)
	flag.StringVar(&packageFlag, "package", "",
		"generated package `name`, defaults to PATH basename",
	)
	flag.Parse()
	if flag.NArg() != 1 {
		flag.Usage()
		os.Exit(2)
	}
	if err := run(flag.Arg(0)); err != nil {
		fmt.Fprintf(os.Stderr, "error: %s\n", err)
		os.Exit(127)
	}
}

func run(bin string) error {
	base := filepath.Base(bin)
	if destFlag == "" {
		destFlag = base
	}
	if packageFlag == "" {
		packageFlag = base
	}

	err := os.MkdirAll(destFlag, 0o755)
	if err != nil && !os.IsExist(err) {
		return err
	}
	output, err = os.OpenFile(
		filepath.Join(destFlag, "memexec.go"),
		os.O_CREATE|os.O_WRONLY|os.O_TRUNC,
		0o644,
	)
	if err != nil {
		return err
	}

	libs := map[string]string{}
	if err := ldd(libs, bin, func(name string) (string, error) {
		return name, nil
	}); err != nil {
		return err
	}
	for name, path := range libs {
		src, err := os.Open(path)
		if err != nil {
			return err
		}
		if name == bin {
			name = base
		}
		dst, err := os.OpenFile(
			filepath.Join(destFlag, name),
			os.O_CREATE|os.O_WRONLY|os.O_TRUNC,
			0o755,
		)
		if err != nil {
			return err
		}
		if _, err := io.Copy(dst, src); err != nil {
			return err
		}
		if err := dst.Close(); err != nil {
			return err
		}
		if err := src.Close(); err != nil {
			return err
		}
	}

	out("// Code generated by memexec-gen. DO NOT EDIT.")
	out("package ", packageFlag)
	out()
	out("import (")
	out(`	_ "embed"`)
	out(`	"os"`)
	out(`	"os/exec"`)
	out(`	"path/filepath"`)
	out()
	out(`	"github.com/amenzhinsky/go-memexec"`)
	out(")")
	out()

	for name := range libs {
		if name == bin {
			name = base
		}
		out("//go:embed ", name)
		out("var ", goName(name), " []byte")
		out()
	}

	out("func New(opts ...memexec.Option) (*memexec.Exec, error) {")
	out(`	temp, err := os.MkdirTemp("", "")`)
	out("	if err != nil {")
	out("		return nil, err")
	out("	}")
	for name := range libs {
		if name == bin {
			continue
		}
		out(`	if err := os.WriteFile(filepath.Join(temp, "`, name, `"), `, goName(name), ", 0o755); err != nil {")
		out("		return nil, err")
		out("	}")
	}
	out("	return memexec.New(", goName(base), ",  append([]memexec.Option{")
	out("		memexec.WithPrepare(func(exe *exec.Cmd) {")
	out(`			exe.Env = append(exe.Env, "LD_LIBRARY_PATH="+temp)`)
	out("		}),")
	out("		memexec.WithCleanup(func() error {")
	out("			return os.RemoveAll(temp)")
	out("		}),")
	out("	}, opts...)...)")
	out("}")

	return nil
}

var output io.Writer

func out(strs ...string) {
	for _, str := range strs {
		if _, err := fmt.Fprint(output, str); err != nil {
			panic(err)
		}
	}
	if _, err := fmt.Fprintln(output); err != nil {
		panic(err)
	}
}

func goName(name string) string {
	name = strings.ReplaceAll(name, ".", "_")
	name = strings.ReplaceAll(name, "-", "_")
	return "memexec_" + name
}

func ldd(
	deps map[string]string, name string, look func(name string) (string, error),
) error {
	path, err := look(name)
	if err != nil {
		return err
	}
	deps[name] = path
	e, err := elf.Open(path)
	if err != nil {
		return err
	}
	l, err := e.ImportedLibraries()
	if err != nil {
		return err
	}
	rpaths, err := e.DynString(elf.DT_RPATH)
	if err != nil {
		return err
	}
	runpaths, err := e.DynString(elf.DT_RUNPATH)
	if err != nil {
		return err
	}
	if err := e.Close(); err != nil {
		return err
	}
	for _, lib := range l {
		if _, ok := deps[lib]; ok {
			continue
		}
		if err := ldd(deps, lib, func(name string) (string, error) {
			return lookLibrary(name, rpaths, runpaths)
		}); err != nil {
			return err
		}
	}
	return nil
}

var ldPaths = []string{"/lib", "/usr/local/lib", "/usr/lib"}

func init() {
	// TODO: os.ReadFile(fmt.Sprintf("/etc/ld-musl-$(ARCH).path"))
	switch runtime.GOARCH {
	case "amd64":
		ldPaths = append(ldPaths,
			"/lib64",
			"/usr/lib64",
			"/usr/local/lib/x86_64-linux-gnu",
			"/lib/x86_64-linux-gnu",
			"/usr/lib/x86_64-linux-gnu",
		)
	case "arm64":
		ldPaths = append(ldPaths,
			"/usr/local/lib/aarch64-linux-gnu",
			"/lib/aarch64-linux-gnu",
			"/usr/lib/aarch64-linux-gnu",
		)
	}
	if s := os.Getenv("LD_LIBRARY_PATH"); s != "" {
		ldPaths = append(ldPaths, filepath.SplitList(s)...)
	}
}

func lookLibrary(name string, rpaths, runpaths []string) (string, error) {
	for _, dir := range append(rpaths, append(ldPaths, runpaths...)...) {
		path := filepath.Join(dir, name)
		stat, err := os.Stat(path)
		if err != nil {
			if os.IsNotExist(err) {
				continue
			}
			return "", err
		}
		if !stat.IsDir() {
			return path, nil
		}
	}
	return "", fmt.Errorf("dynamic library %s not found", name)
}


================================================
FILE: go.mod
================================================
module github.com/amenzhinsky/go-memexec

go 1.19

require golang.org/x/sys v0.0.0-20210903071746-97244b99971b


================================================
FILE: go.sum
================================================
golang.org/x/sys v0.0.0-20210903071746-97244b99971b h1:3Dq0eVHn0uaQJmPO+/aYPI/fRMqdrVDbu7MQcku54gg=
golang.org/x/sys v0.0.0-20210903071746-97244b99971b/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=


================================================
FILE: memexec.go
================================================
package memexec

import (
	"context"
	"os"
	"os/exec"
)

type Option func(e *Exec)

// Exec is an in-memory executable code unit.
type Exec struct {
	f     *os.File
	opts  []func(cmd *exec.Cmd)
	clean func() error
}

// WithPrepare configures cmd with default values such as Env, Dir, etc.
func WithPrepare(fn func(cmd *exec.Cmd)) Option {
	return func(e *Exec) {
		e.opts = append(e.opts, fn)
	}
}

// WithCleanup is executed right after Exec.Close.
func WithCleanup(fn func() error) Option {
	return func(e *Exec) {
		e.clean = fn
	}
}

// New creates new memory execution object that can be
// used for executing commands on a memory based binary.
func New(b []byte, opts ...Option) (*Exec, error) {
	f, err := open(b)
	if err != nil {
		return nil, err
	}
	e := &Exec{f: f}
	for _, opt := range opts {
		opt(e)
	}
	return e, nil
}

// Command is an equivalent of `exec.Command`,
// except that the path to the executable is being omitted.
func (m *Exec) Command(args ...string) *exec.Cmd {
	return m.CommandContext(context.Background(), args...)
}

// CommandContext is an equivalent of `exec.CommandContext`,
// except that the path to the executable is being omitted.
func (m *Exec) CommandContext(ctx context.Context, args ...string) *exec.Cmd {
	exe := exec.CommandContext(ctx, m.f.Name(), args...)
	for _, opt := range m.opts {
		opt(exe)
	}
	return exe
}

// Close closes Exec object.
//
// Any further command will fail, it's client's responsibility
// to control the flow by using synchronization algorithms.
func (m *Exec) Close() error {
	if err := clean(m.f); err != nil {
		if m.clean != nil {
			_ = m.clean()
		}
		return err
	}
	if m.clean == nil {
		return nil
	}
	return m.clean()
}


================================================
FILE: memexec_all.go
================================================
//go:build !linux
// +build !linux

package memexec

import (
	"os"
	"runtime"
)

func open(b []byte) (*os.File, error) {
	pattern := "go-memexec-"
	if runtime.GOOS == "windows" {
		pattern = "go-memexec-*.exe"
	}
	f, err := os.CreateTemp("", pattern)
	if err != nil {
		return nil, err
	}
	defer func() {
		if err != nil {
			_ = clean(f)
		}
	}()
	if err = os.Chmod(f.Name(), 0o500); err != nil {
		return nil, err
	}
	if _, err = f.Write(b); err != nil {
		return nil, err
	}
	if err = f.Close(); err != nil {
		return nil, err
	}
	return f, nil
}

func clean(f *os.File) error {
	return os.Remove(f.Name())
}


================================================
FILE: memexec_linux.go
================================================
//go:build linux
// +build linux

package memexec

import (
	"fmt"
	"os"

	"golang.org/x/sys/unix"
)

func open(b []byte) (*os.File, error) {
	fd, err := unix.MemfdCreate("", unix.MFD_CLOEXEC)
	if err != nil {
		return nil, err
	}
	f := os.NewFile(uintptr(fd), fmt.Sprintf("/proc/%d/fd/%d", os.Getpid(), fd))
	if _, err := f.Write(b); err != nil {
		_ = f.Close()
		return nil, err
	}
	return f, nil
}

func clean(f *os.File) error {
	return f.Close()
}


================================================
FILE: memexec_linux_test.go
================================================
//go:build linux

package memexec

import (
	"os/exec"
	"testing"
)

func TestGenLinux(t *testing.T) {
	e := exec.Command("go", "run", "../cmd/memexec-gen", "/usr/bin/python3")
	e.Dir = "testdata"
	_ = runCommand(t, e)

	e = exec.Command("go", "run", ".", "-c", "print(42)")
	e.Dir = "testdata"
	if have := runCommand(t, e); have != "42" {
		t.Fatalf("output mismatch:\n\thave: %s\n\twant: %s", have, "42")
	}
}


================================================
FILE: memexec_test.go
================================================
package memexec

import (
	"bytes"
	"context"
	"os"
	"os/exec"
	"runtime"
	"strings"
	"testing"
	"time"
)

func TestCommand(t *testing.T) {
	exe := newEchoExec(t)
	defer func() {
		if err := exe.Close(); err != nil {
			t.Fatalf("close error: %s", err)
		}
	}()

	c := exe.Command("test")
	if have := runCommand(t, c); !strings.HasPrefix(have, "test") {
		t.Errorf("command output = %q doesn't contain %q", have, "test")
	}
}

func TestCommand_Shell(t *testing.T) {
	if runtime.GOOS == "windows" {
		return
	}

	exe, err := New([]byte("#!/bin/sh\necho hello"))
	if err != nil {
		panic(err)
	}
	defer exe.Close()

	b, err := exe.Command().CombinedOutput()
	if err != nil {
		t.Fatalf("err = %v, output = %q", err, b)
	}
	if !bytes.Equal(b, []byte("hello\n")) {
		t.Fatalf("output = %q, want %q", string(b), []byte("hello\n"))
	}
}

func TestCommandContext(t *testing.T) {
	// the test is failing on windows, probably due to missing sleep command,
	// unfortunately I have no windows machines around to fix this
	if runtime.GOOS == "windows" {
		return
	}

	exe := newSleepExec(t)
	defer func() {
		if err := exe.Close(); err != nil {
			t.Fatalf("close error: %s", err)
		}
	}()

	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond*500)
	defer cancel()

	c := exe.CommandContext(ctx, "1")

	start := time.Now()
	if err := c.Start(); err != nil {
		t.Fatalf("start failed: %s", err)
	}
	if err := c.Wait(); err != nil && err.Error() != "signal: killed" {
		t.Fatalf("command execution failed: %s", err)
	}
	stop := time.Now()
	if delta := stop.Sub(start); delta > time.Millisecond*600 || delta < time.Millisecond*500 {
		t.Fatalf("unexpected command execution time: delta=%s", delta)
	}
}

func BenchmarkCommand(b *testing.B) {
	exe := newEchoExec(b)
	defer func() {
		if err := exe.Close(); err != nil {
			b.Fatalf("close error: %s", err)
		}
	}()

	for i := 0; i < b.N; i++ {
		cmd := exe.Command("test")
		if _, err := cmd.Output(); err != nil {
			b.Fatal(err)
		}
	}
}

func newExec(t testing.TB, name string) *Exec {
	path, err := exec.LookPath(name)
	if err != nil {
		t.Fatal(err)
	}
	b, err := os.ReadFile(path)
	if err != nil {
		t.Fatal(err)
	}

	exe, err := New(b)
	if err != nil {
		t.Fatal(err)
	}
	return exe
}

func newEchoExec(t testing.TB) *Exec {
	// lookup echo binary that is provided on all unix systems
	// and it's not a built-in opposed to `ls` and `type`
	return newExec(t, "echo")
}

func newSleepExec(t testing.TB) *Exec {
	return newExec(t, "sleep")
}

func runCommand(t *testing.T, cmd *exec.Cmd) string {
	t.Helper()
	b, err := cmd.CombinedOutput()
	if err != nil {
		if b != nil {
			t.Fatalf("failed to run: %q", string(b))
		}
		t.Fatal(err)
	}
	return string(b)
}


================================================
FILE: testdata/.gitignore
================================================
python3


================================================
FILE: testdata/main.go
================================================
package main

import (
	"fmt"
	"os"
	"strings"

	"github.com/amenzhinsky/go-memexec/testdata/python3"
)

func main() {
	exe, err := python3.New()
	if err != nil {
		panic(err)
	}
	c := exe.Command(os.Args[1:]...)
	c.Stdin = os.Stdin
	b, err := c.CombinedOutput()
	if err != nil {
		panic(err)
	}
	fmt.Print(strings.TrimSpace(string(b)))
}