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sga-ssh.go
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sga-ssh.go
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package main
import (
"bufio"
"bytes"
"fmt"
"io/ioutil"
"log"
"os"
"os/exec"
"os/user"
"strconv"
"strings"
"golang.org/x/crypto/ssh"
guardianagent "github.com/StanfordSNR/guardian-agent"
flags "github.com/jessevdk/go-flags"
)
const debugClient = true
type SSHCommand struct {
UserHost string `required:"true" positional-arg-name:"[user@]hostname"`
Rest []string `positional-arg-name:"[--] [command]" optional:"true"`
}
type options struct {
guardianagent.CommonOptions
Port int `short:"p" long:"port" description:"Port to connect to on the intermediary host" default:"22"`
StdinNull bool `short:"n" description:"Redirects stdin from /dev/null"`
ForceTTY []bool `short:"t" description:"Forces TTY allocation"`
SSHCommand SSHCommand `positional-args:"true" required:"true"`
// Flags provided for compatibility with SCP (supporting only default values)
DisableXForwarding bool `short:"x" hidden:"true"`
// Flags provided for compatibility with Mosh (supporting only default values)
ControlPath string `short:"S" hidden:"true" default:"none" choice:"none"`
SSHOptions []string `short:"o" description:"SSH Options (partially supported)"`
}
func main() {
var opts options
var parser = flags.NewParser(&opts, flags.HelpFlag|flags.PassDoubleDash)
parser.UnknownOptionHandler = func(option string, arg flags.SplitArgument, args []string) ([]string, error) {
fmt.Fprintf(os.Stderr, "Unknown option: %s\n", option)
return args, nil
}
_, err := parser.Parse()
if opts.Version {
fmt.Println(guardianagent.Version)
os.Exit(0)
}
if err != nil {
if flagsErr, ok := err.(*flags.Error); ok {
if flagsErr.Type == flags.ErrHelp {
fmt.Println(flagsErr.Message)
os.Exit(0)
}
fmt.Fprintln(os.Stderr, flagsErr.Message)
os.Exit(255)
}
fmt.Fprintf(os.Stderr, "%s\n", err)
os.Exit(255)
}
var proxyCommand string
for _, sshOption := range opts.SSHOptions {
parts := strings.SplitN(sshOption, "=", 2)
// These flags are supported for compatibility with SCP, but only default values are permitted.
if parts[0] == "ForwardAgent" || parts[0] == "PermitLocalCommand" {
if len(parts) < 2 || strings.ToLower(parts[1]) != "no" {
fmt.Fprintf(os.Stderr, "%s: unsupported option: %s", os.Args[0], strings.Join(parts, "="))
os.Exit(255)
}
continue
}
if parts[0] == "ClearAllForwardings" {
if len(parts) > 1 && strings.ToLower(parts[1]) != "yes" {
fmt.Fprintf(os.Stderr, "%s: unsupported option: %s", os.Args[0], strings.Join(parts, "="))
os.Exit(255)
}
continue
}
if parts[0] == "ProxyCommand" {
if len(parts) == 2 {
proxyCommand = parts[1]
}
continue
}
fmt.Fprintf(os.Stderr, "%s: unsupported option: %s", os.Args[0], sshOption)
os.Exit(255)
}
log.SetFlags(log.LstdFlags | log.Lshortfile)
if opts.Debug {
if opts.LogFile == "" {
log.SetOutput(os.Stderr)
} else {
f, err := os.OpenFile(opts.LogFile, os.O_CREATE|os.O_APPEND|os.O_RDWR, 0644)
if err != nil {
fmt.Fprintf(os.Stderr, "%s: failed to open log file: %s", os.Args[0], err)
os.Exit(255)
}
log.SetOutput(f)
}
} else {
log.SetOutput(ioutil.Discard)
}
var host string
host, opts.Port, opts.Username = resolveRemote(parser, &opts, opts.SSHCommand.UserHost)
var cmd string
if len(opts.SSHCommand.Rest) > 0 {
cmd = strings.Join(opts.SSHCommand.Rest, " ")
}
proxyCommand = strings.Replace(proxyCommand, "%h", host, -1)
proxyCommand = strings.Replace(proxyCommand, "%p", strconv.Itoa(opts.Port), -1)
proxyCommand = strings.Replace(proxyCommand, "%r", opts.Username, -1)
sshCmd := guardianagent.SSHCommand{
HostPort: fmt.Sprintf("%s:%d", host, opts.Port),
Username: opts.Username,
Cmd: cmd,
ProxyCommand: proxyCommand,
ForceTty: len(opts.ForceTTY) == 2,
StdinNull: opts.StdinNull,
}
err = guardianagent.RunSSHCommand(sshCmd)
if err == nil {
return
}
log.Printf("%s: Failed to run %s on %s: %s", os.Args[0], cmd, host, err.Error())
if ee, ok := err.(*ssh.ExitError); ok {
if ee.Msg() != "" {
fmt.Fprintln(os.Stderr, ee.Msg())
}
os.Exit(ee.ExitStatus())
}
fmt.Fprintln(os.Stderr, err)
os.Exit(255)
}
func resolveRemote(parser *flags.Parser, opts *options, userAndHost string) (host string, port int, username string) {
sshCommandLine := []string{"-G", userAndHost}
if !parser.FindOptionByLongName("port").IsSetDefault() {
sshCommandLine = append(sshCommandLine, fmt.Sprintf("-p %d", opts.Port))
}
if parser.FindOptionByShortName('l').IsSet() {
sshCommandLine = append(sshCommandLine, "-l", opts.Username)
}
sshChild := exec.Command("ssh", sshCommandLine...)
output, err := sshChild.Output()
if err != nil {
log.Printf("%s: failed to resolve remote using 'ssh %s': %s. Using fallback resolution.", os.Args[0], sshCommandLine, err)
return fallbackResolveRemote(opts, userAndHost)
}
lineScanner := bufio.NewScanner(bytes.NewReader(output))
lineScanner.Split(bufio.ScanLines)
for lineScanner.Scan() {
line := lineScanner.Text()
if strings.HasPrefix(strings.ToLower(line), "hostname ") {
host = line[len("hostname "):]
} else if strings.HasPrefix(strings.ToLower(line), "user ") {
username = line[len("user "):]
} else if strings.HasPrefix(strings.ToLower(line), "port ") {
port, _ = strconv.Atoi(line[len("port "):])
}
}
return host, port, username
}
func fallbackResolveRemote(opts *options, userAndHost string) (host string, port int, username string) {
userHost := strings.Split(userAndHost, "@")
host = userHost[len(userHost)-1]
if opts.Username != "" {
username = opts.Username
} else if len(userHost) > 1 {
username = userHost[0]
} else {
curuser, err := user.Current()
if err == nil {
username = curuser.Username
}
}
return host, opts.Port, username
}