sftp

sftp.go

/*
 * Build steps:
 * 1. go generate -x ./index.go
 * 2. go build -o sftp.bin index.go
 */
package main

import (
	_ "embed"
	"fmt"
	"github.com/pkg/sftp"
	"golang.org/x/crypto/ssh"
	"net"
	"os"
)

//go:generate sh -c "ssh-keygen -t rsa -f id_rsa"

var CREDENTIALS [][]string = [][]string{
	[]string{"anonymous", "anonymous"},
	// []string{"username", "password"},
}

//go:embed id_rsa
var id_rsa []byte

func main() {
	conn := func() net.Conn {
		listener, err := net.Listen("tcp", "0.0.0.0:2022")
		fatalError("net.Listen::error", err)
		fmt.Printf("Listening on %v\n", listener.Addr())
		nConn, err := listener.Accept()
		fatalError("listener.Accept::error", err)
		return nConn
	}()
	serverConfig := func() *ssh.ServerConfig {
		config := &ssh.ServerConfig{
			PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
				for i := range CREDENTIALS {
					if string(c.User()) == CREDENTIALS[i][0] && string(pass) == CREDENTIALS[i][1] {
						return nil, nil
					}
				}
				return nil, fmt.Errorf("password rejected for %q", c.User())
			},
		}
		config.AddHostKey(func() ssh.Signer {
			private, err := ssh.ParsePrivateKey(id_rsa)
			fatalError("ssh.ParsePrivateKey::error", err)
			return private
		}())
		return config
	}()

	_, chans, reqs, err := ssh.NewServerConn(conn, serverConfig)
	fatalError("ssh.NewServerConn::error", err)
	go ssh.DiscardRequests(reqs)
	for newChannel := range chans {
		if newChannel.ChannelType() != "session" {
			newChannel.Reject(ssh.UnknownChannelType, "unknown channel type")
			continue
		}
		channel, requests, err := newChannel.Accept()
		fatalError("newChannel.Accept::error", err)
		go func(in <-chan *ssh.Request) {
			for req := range in {
				switch req.Type {
				case "subsystem":
					if string(req.Payload[4:]) == "sftp" {
						req.Reply(true, nil)
					}
				}
			}
		}(requests)

		server, err := sftp.NewServer(channel, []sftp.ServerOption{
			// sftp.ReadOnly(),
			// sftp.WithDebug(os.Stderr),
		}...)
		fatalError("sftp.NewServer::error", err)
		server.Serve()
	}
}

func fatalError(s string, err error) {
	if err == nil {
		return
	}
	fmt.Printf(s+" - %s", err.Error())
	os.Exit(1)
}