docker/archive.go

package docker

import (
	"errors"
	"io"
	"io/ioutil"
	"os"
	"os/exec"
)

type Archive io.Reader

type Compression uint32

const (
	Uncompressed Compression = iota
	Bzip2
	Gzip
	Xz
)

func (compression *Compression) Flag() string {
	switch *compression {
	case Bzip2:
		return "j"
	case Gzip:
		return "z"
	case Xz:
		return "J"
	}
	return ""
}

func Tar(path string, compression Compression) (io.Reader, error) {
	cmd := exec.Command("bsdtar", "-f", "-", "-C", path, "-c"+compression.Flag(), ".")
	return CmdStream(cmd)
}

func Untar(archive io.Reader, path string) error {
	cmd := exec.Command("bsdtar", "-f", "-", "-C", path, "-x")
	cmd.Stdin = archive
	output, err := cmd.CombinedOutput()
	if err != nil {
		return errors.New(err.Error() + ": " + string(output))
	}
	return nil
}

// CmdStream executes a command, and returns its stdout as a stream.
// If the command fails to run or doesn't complete successfully, an error
// will be returned, including anything written on stderr.
func CmdStream(cmd *exec.Cmd) (io.Reader, error) {
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, err
	}
	stderr, err := cmd.StderrPipe()
	if err != nil {
		return nil, err
	}
	pipeR, pipeW := io.Pipe()
	errChan := make(chan []byte)
	// Collect stderr, we will use it in case of an error
	go func() {
		errText, e := ioutil.ReadAll(stderr)
		if e != nil {
			errText = []byte("(...couldn't fetch stderr: " + e.Error() + ")")
		}
		errChan <- errText
	}()
	// Copy stdout to the returned pipe
	go func() {
		_, err := io.Copy(pipeW, stdout)
		if err != nil {
			pipeW.CloseWithError(err)
		}
		errText := <-errChan
		if err := cmd.Wait(); err != nil {
			pipeW.CloseWithError(errors.New(err.Error() + ": " + string(errText)))
		} else {
			pipeW.Close()
		}
	}()
	// Run the command and return the pipe
	if err := cmd.Start(); err != nil {
		return nil, err
	}
	return pipeR, nil
}

// NewTempArchive reads the content of src into a temporary file, and returns the contents
// of that file as an archive. The archive can only be read once - as soon as reading completes,
// the file will be deleted.
func NewTempArchive(src Archive, dir string) (*TempArchive, error) {
	f, err := ioutil.TempFile(dir, "")
	if err != nil {
		return nil, err
	}
	if _, err := io.Copy(f, src); err != nil {
		return nil, err
	}
	if _, err := f.Seek(0, 0); err != nil {
		return nil, err
	}
	st, err := f.Stat()
	if err != nil {
		return nil, err
	}
	size := st.Size()
	return &TempArchive{f, size}, nil
}

type TempArchive struct {
	*os.File
	Size int64 // Pre-computed from Stat().Size() as a convenience
}

func (archive *TempArchive) Read(data []byte) (int, error) {
	n, err := archive.File.Read(data)
	if err != nil {
		os.Remove(archive.File.Name())
	}
	return n, err
}