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@tobgu
Last active October 5, 2023 12:14
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Remote ssh exec using Go
package main
import (
"bufio"
"fmt"
"golang.org/x/crypto/ssh"
"io"
"log"
"os"
"strconv"
"strings"
"syscall"
"time"
)
/**
Compile: go build remotessh.go
Call as client: ./remotessh
Call as target: ./remotessh <exit code>
*/
const privateKey = `
-----BEGIN OPENSSH PRIVATE KEY-----
<< private key >>
-----END OPENSSH PRIVATE KEY-----
`
// Dummy logger for stdout and stderr
type MyReader struct {
prefix string
}
func (r MyReader) Write(src []byte) (int, error) {
fmt.Println(r.prefix, string(src))
return len(src), nil
}
type MyWriter struct {
data string
offset int
}
func (w *MyWriter) Read(dst []byte) (int, error) {
if w.offset >= len(w.data) {
return 0, io.EOF
}
length := copy(dst, w.data[w.offset:])
w.offset += length
return length, nil
}
func main() {
if len(os.Args) > 1 {
// Act as basic programmable command
fmt.Fprintf(os.Stdout, "Some output to stdout\n")
fmt.Fprintf(os.Stderr, "Some other output to stderr\n")
// Read from stdin until end marker is reached
scanner := bufio.NewScanner(os.Stdin)
buf := ""
for scanner.Scan() {
buf += scanner.Text()
if strings.Contains(buf, "<<end>>") {
break
}
}
if err := scanner.Err(); err != nil {
fmt.Fprintf(os.Stderr,"Error reading from stdin: %v", err)
} else {
fmt.Fprintf(os.Stdout, "Received on stdin: %s", buf)
}
code, _ := strconv.Atoi(os.Args[1])
syscall.Exit(code)
}
key, err := ssh.ParsePrivateKey([]byte(privateKey))
if err != nil {
log.Fatalf("Parse key: %v", err)
}
config := &ssh.ClientConfig{
User: "tobias",
Auth: []ssh.AuthMethod{
ssh.PublicKeys(key),
},
HostKeyCallback: ssh.InsecureIgnoreHostKey(),
}
client, err := ssh.Dial("tcp", "localhost:22", config)
if err != nil {
log.Fatal("Failed to dial: ", err)
}
// Each ClientConn can support multiple interactive sessions,
// represented by a Session.
session, err := client.NewSession()
if err != nil {
log.Fatal("Failed to create session: ", err)
}
defer session.Close()
// Output and input
session.Stdout = MyReader{prefix: "stdout:"}
session.Stderr = MyReader{prefix: "stderr:"}
session.Stdin = &MyWriter{data: "Some input, some more input, the <<end>>"}
t0 := time.Now()
err = session.Start("<path to remotessh>/remotessh 1")
if err != nil {
log.Fatalf("Error starting command: %v", err)
}
err = session.Wait()
if err != nil {
if e, ok := err.(*ssh.ExitError); ok {
fmt.Printf("ExitError, status: %d, signal: %s, message: %s\n", e.ExitStatus(), e.Signal(), e.Msg())
} else {
fmt.Printf("Unknown error, %v", e)
}
}
fmt.Println("Time taken", time.Since(t0).Seconds(), "s")
}
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