ssh_mock.go

/*
Copyright 2016 The Kubernetes Authors All rights reserved.

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 tests

import (
	"bytes"
	"crypto/rand"
	"crypto/rsa"
	"io"
	"net"
	"strconv"

	"github.com/golang/glog"
	"github.com/pkg/errors"
	"golang.org/x/crypto/ssh"
)

// SSHServer provides a mock SSH Server for testing. Commands are stored, not executed.
type SSHServer struct {
	Config *ssh.ServerConfig
	// Commands stores the raw commands executed against the server.
	Commands             map[string]int
	Connected            bool
	Transfers            *bytes.Buffer
	HadASessionRequested bool
	// CommandsToOutput can be used to mock what the SSHServer returns for a given command
	CommandToOutput map[string]string
}

// NewSSHServer returns a NewSSHServer instance, ready for use.
func NewSSHServer() (*SSHServer, error) {
	s := &SSHServer{}
	s.Transfers = &bytes.Buffer{}
	s.Config = &ssh.ServerConfig{
		NoClientAuth: true,
	}
	s.Commands = make(map[string]int)

	private, err := rsa.GenerateKey(rand.Reader, 2014)
	if err != nil {
		return nil, errors.Wrap(err, "Error generating RSA key")
	}
	signer, err := ssh.NewSignerFromKey(private)
	if err != nil {
		return nil, errors.Wrap(err, "Error creating signer from key")
	}
	s.Config.AddHostKey(signer)
	return s, nil
}

type execRequest struct {
	Command string
}

// Start starts the mock SSH Server, and returns the port it's listening on.
func (s *SSHServer) Start() (int, error) {
	listener, err := net.Listen("tcp", "127.0.0.1:0")
	if err != nil {
		return 0, errors.Wrap(err, "Error creating tcp listener for ssh server")
	}

	// Main loop, listen for connections and store the commands.
	go func() {
		for {
			nConn, err := listener.Accept()
			go func() {
				if err != nil {
					return
				}

				_, chans, reqs, err := ssh.NewServerConn(nConn, s.Config)
				if err != nil {
					return
				}
				// The incoming Request channel must be serviced.
				go ssh.DiscardRequests(reqs)

				// Service the incoming Channel channel.
				for newChannel := range chans {
					if newChannel.ChannelType() == "session" {
						s.HadASessionRequested = true
					}
					channel, requests, err := newChannel.Accept()
					s.Connected = true
					if err != nil {
						return
					}

					req := <-requests
					req.Reply(true, nil)

					//Note: string(req.Payload) adds additional characters to start of input, execRequest used to solve this issue
					var cmd execRequest
					if err := ssh.Unmarshal(req.Payload, &cmd); err != nil {
						glog.Errorln("Unmarshall encountered error: %s", err)
						return
					}
					s.Commands[cmd.Command] = 1

					// Write specified command output as mocked ssh output
					if val, ok := s.CommandToOutput[cmd.Command]; ok {
						channel.Write([]byte(val))
					}
					channel.SendRequest("exit-status", false, []byte{0, 0, 0, 0})

					// Store anything that comes in over stdin.
					io.Copy(s.Transfers, channel)
					channel.Close()
				}
			}()
		}
	}()

	// Parse and return the port.
	_, p, err := net.SplitHostPort(listener.Addr().String())
	if err != nil {
		return 0, errors.Wrap(err, "Error splitting host port")
	}
	port, err := strconv.Atoi(p)
	if err != nil {
		return 0, errors.Wrap(err, "Error converting port string to integer")
	}
	return port, nil
}