go sftp client sample

.env

sftp.user=xxx
sftp.connection=xxxx:port-num
sftp.private_key_path=xxx

sftp.go

package util

import (
	"io"
	"io/ioutil"
	"log"
	"os"

	"github.com/pkg/sftp"
	"golang.org/x/crypto/ssh"

	"github.com/joho/godotenv"
	"golang.org/x/text/encoding"
	"golang.org/x/text/transform"
)

var (
	userName    string
	serverConn  string
	keyFilePath string
)

func init() {
	err := godotenv.Load(".env")
	if err != nil {
		log.Fatalf("Error loading .env file: %v", err)
	}

	userName = os.Getenv("sftp.user")
	serverConn = os.Getenv("sftp.connection")
	keyFilePath = os.Getenv("sftp.private_key_path")
}

func download(targetPath string, encoding encoding.Encoding) ([]byte, error) {
	publicKey, err := sshPublicKeyFile(keyFilePath)
	if err != nil {
		return nil, err
	}
	config := &ssh.ClientConfig{
		User:            userName,
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
		Auth: []ssh.AuthMethod{
			publicKey,
		},
	}
	config.SetDefaults()

	sshConn, err := ssh.Dial("tcp", serverConn, config)
	if err != nil {
		return nil, err
	}
	defer sshConn.Close()

	client, err := sftp.NewClient(sshConn)
	if err != nil {
		return nil, err
	}
	defer client.Close()

	r, err := client.Open(targetPath)
	if err != nil {
		return nil, err
	}
	defer r.Close()

	decodedReader := io.Reader(r)
	if encoding != nil {
		decodedReader = transform.NewReader(r, encoding.NewDecoder())
	}
	buf, err := ioutil.ReadAll(decodedReader)
	return buf, err
}

func sshPublicKeyFile(filePath string) (ssh.AuthMethod, error) {
	buffer, err := ioutil.ReadFile(filePath)
	if err != nil {
		return nil, err
	}

	key, err := ssh.ParsePrivateKey(buffer)
	if err != nil {
		return nil, err
	}
	return ssh.PublicKeys(key), nil
}

sftp_test.go

package util

import (
	"fmt"
	"testing"

	"golang.org/x/text/encoding/japanese"
)

func TestDownload(t *testing.T) {
	buf, err := download("/share/xxxxs.csv", japanese.ShiftJIS)
	if err != nil {
		message := fmt.Sprintf("error happened: %v", err)
		t.Fatal(message)
	}

	fmt.Printf("file context\n: %s", string(buf))
}