Golang SFTP Client: Download File, Upload File Example

Golang SFTP client examples


Golang SFTP ClientBuilding a Golang SFTP client is common when automating network systems. The github.com/pkg/sftp package is a fine tuned package that can get the job done. It works with SSH version 2 and is compatible with OpenSSH and other SSH spec servers.

Client setup may differ depending on your authentication requirements. In each example you’ll notice the HostKeyCallback to setup a FixedHostKey references the target host public key; this is used to prevent spoofing. If your host public key isn’t already archived in the your home directory OpenSSH known_hosts file, you can run ssh-keyscan to pull it off the target host.

Overview

Copy File Local to Remote

Here’s a simple example that copies a local file to a remote SFTP location.

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package main
 
import (
"github.com/pkg/sftp"
"golang.org/x/crypto/ssh"
"io"
"log"
"os"
"strings"
"bufio"
"fmt"
"path/filepath"
)
 
func main() {
 
user   := ""
pass   := ""
remote := ""
port   := ":22"
 
// get host public key
hostKey := getHostKey(remote)
 
config := &ssh.ClientConfig{
User: user,
Auth: []ssh.AuthMethod{
ssh.Password(pass),
},
// HostKeyCallback: ssh.InsecureIgnoreHostKey(),
HostKeyCallback: ssh.FixedHostKey(hostKey),
}
 
// connect
conn, err := ssh.Dial("tcp", remote+port, config)
if err != nil {
   log.Fatal(err)
}
defer conn.Close()
 
// create new SFTP client
client, err := sftp.NewClient(conn)
if err != nil {
   log.Fatal(err)
}
defer client.Close()
 
// create destination file
dstFile, err := client.Create("./file.txt")
if err != nil {
   log.Fatal(err)
}
defer dstFile.Close()
 
// create source file
srcFile, err := os.Open("./file.txt")
if err != nil {
   log.Fatal(err)
}
 
// copy source file to destination file
bytes, err := io.Copy(dstFile, srcFile)
if err != nil {
   log.Fatal(err)
}
fmt.Printf("%d bytes copied\n", bytes)
}
 
func getHostKey(host string) ssh.PublicKey {
// parse OpenSSH known_hosts file
// ssh or use ssh-keyscan to get initial key
file, err := os.Open(filepath.Join(os.Getenv("HOME"), ".ssh", "known_hosts"))
if err != nil {
log.Fatal(err)
}
defer file.Close()
 
scanner := bufio.NewScanner(file)
var hostKey ssh.PublicKey
for scanner.Scan() {
fields := strings.Split(scanner.Text(), " ")
if len(fields) != 3 {
continue
}
if strings.Contains(fields[0], host) {
var err error
hostKey, _, _, _, err = ssh.ParseAuthorizedKey(scanner.Bytes())
if err != nil {
log.Fatalf("error parsing %q: %v", fields[2], err)
}
break
}
}
 
if hostKey == nil {
log.Fatalf("no hostkey found for %s", host)
}
 
return hostKey
}

Copy File Remote to Local

Here’s a simple example that copies a remote file from an SFTP local to a local location.

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package main
 
import (
"github.com/pkg/sftp"
"golang.org/x/crypto/ssh"
"io"
"log"
"os"
"strings"
"bufio"
"fmt"
"path/filepath"
)
 
func main() {
 
user   := ""
pass   := ""
remote := ""
port   := ":22"
 
// get host public key
hostKey := getHostKey(remote)
 
config := &ssh.ClientConfig{
User: user,
Auth: []ssh.AuthMethod{
ssh.Password(pass),
},
// HostKeyCallback: ssh.InsecureIgnoreHostKey(),
HostKeyCallback: ssh.FixedHostKey(hostKey),
}
 
// connect
conn, err := ssh.Dial("tcp", remote+port, config)
if err != nil {
   log.Fatal(err)
}
defer conn.Close()
 
// create new SFTP client
client, err := sftp.NewClient(conn)
if err != nil {
   log.Fatal(err)
}
defer client.Close()
 
// create destination file
dstFile, err := os.Create("./file.txt")
if err != nil {
   log.Fatal(err)
}
defer dstFile.Close()
 
// open source file
srcFile, err := client.Open("./file.txt")
if err != nil {
   log.Fatal(err)
}
 
// copy source file to destination file
bytes, err := io.Copy(dstFile, srcFile)
if err != nil {
   log.Fatal(err)
}
fmt.Printf("%d bytes copied\n", bytes)
 
// flush in-memory copy
err = dstFile.Sync()
if err != nil {
   log.Fatal(err)
}
}
 
func getHostKey(host string) ssh.PublicKey {
// parse OpenSSH known_hosts file
// ssh or use ssh-keyscan to get initial key
file, err := os.Open(filepath.Join(os.Getenv("HOME"), ".ssh", "known_hosts"))
if err != nil {
log.Fatal(err)
}
defer file.Close()
 
scanner := bufio.NewScanner(file)
var hostKey ssh.PublicKey
for scanner.Scan() {
fields := strings.Split(scanner.Text(), " ")
if len(fields) != 3 {
continue
}
if strings.Contains(fields[0], host) {
var err error
hostKey, _, _, _, err = ssh.ParseAuthorizedKey(scanner.Bytes())
if err != nil {
log.Fatalf("error parsing %q: %v", fields[2], err)
}
break
}
}
 
if hostKey == nil {
log.Fatalf("no hostkey found for %s", host)
}
 
return hostKey
}

See also:
Golang DNS Lookup
Golang IP Address Manipulation
Golang Regular Expression Match
Golang SSH Client: Multiple Commands