teleport/lib/srv/exec.go

/*
Copyright 2015 Gravitational, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
package srv

import (
	"bytes"
	"fmt"
	"io"
	"os"
	"os/exec"
	"syscall"

	"github.com/gravitational/teleport/lib/events"
	"github.com/gravitational/trace"
	"golang.org/x/crypto/ssh"
)

type execResult struct {
	command string
	code    int
}

type execReq struct {
	Command string
}

type execFn struct {
	cmdName string
	cmd     *exec.Cmd
	ctx     *ctx

	// TODO(klizhentas) implement capturing as a thread safe factored out feature
	// what is important is that writes and reads to buffer should be protected
	// out contains captured command output
	out *bytes.Buffer
}

func parseExecRequest(req *ssh.Request, ctx *ctx) (*execFn, error) {
	var e execReq
	if err := ssh.Unmarshal(req.Payload, &e); err != nil {
		return nil, fmt.Errorf("failed to parse exec request, error: %v", err)
	}
	return &execFn{
		ctx:     ctx,
		cmdName: e.Command,
		out:     &bytes.Buffer{},
	}, nil
}

func (e *execFn) String() string {
	return fmt.Sprintf("Exec(cmd=%v)", e.cmdName)
}

// execute is a blocking execution of a command
func (e *execFn) start(sconn *ssh.ServerConn, shell string, ch ssh.Channel) (*execResult, error) {
	e.cmd = exec.Command(shell, []string{"-c", e.cmdName}...)
	//e.cmd = exec.Command(e.cmdName)
	// we capture output to the buffer
	e.cmd.Stdout = io.MultiWriter(e.out, ch)
	e.cmd.Stderr = io.MultiWriter(e.out, ch)
	// TODO(klizhentas) figure out the way to see if stdin is ever needed.
	// e.cmd.Stdin = ch leads to the following problem:
	// e.cmd.Wait() never returns  because stdin never gets closed or never reached
	// see cmd.Stdin comments
	e.cmd.Stdin = nil

	e.cmd.Env = []string{
		"TERM=xterm",
		"HOME=" + os.Getenv("HOME"),
		"USER=" + sconn.User(),
	}

	err := setCmdUser(e.cmd, sconn.User())
	if err != nil {
		return nil, trace.Wrap(err)
	}

	if err := e.cmd.Start(); err != nil {
		e.ctx.Warningf("%v start failure err: %v", e, err)
		return e.collectStatus(e.cmd, err)
	}
	e.ctx.Infof("%v started", e)
	return nil, nil
}

func (e *execFn) collectStatus(cmd *exec.Cmd, err error) (*execResult, error) {
	status, err := collectStatus(e.cmd, err)
	if err != nil {
		e.ctx.emit(events.NewExec(e.cmdName, e.out, -1, err))
	} else {
		e.ctx.emit(events.NewExec(e.cmdName, e.out, status.code, err))
	}
	return status, err
}

func (e *execFn) wait() (*execResult, error) {
	if e.cmd.Process == nil {
		e.ctx.Errorf("no process")
	}
	return e.collectStatus(e.cmd, e.cmd.Wait())
}

func collectStatus(cmd *exec.Cmd, err error) (*execResult, error) {
	if err != nil {
		if exitErr, ok := err.(*exec.ExitError); ok {
			status := exitErr.Sys().(syscall.WaitStatus)
			return &execResult{code: status.ExitStatus(), command: cmd.Path}, nil
		}
		return nil, err
	}
	status, ok := cmd.ProcessState.Sys().(syscall.WaitStatus)
	if !ok {
		return nil, fmt.Errorf("unspoorted exit status: %T(%v)", cmd.ProcessState.Sys(), cmd.ProcessState.Sys())
	}
	return &execResult{code: status.ExitStatus(), command: cmd.Path}, nil
}