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// An example SFTP server implementation using the golang SSH package.
// Serves the whole filesystem visible to the user, and has a hard-coded username and password,
// so not for real use!
package main
import (
"flag"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"os"
"github.com/pkg/sftp"
"golang.org/x/crypto/ssh"
)
// Based on example server code from golang.org/x/crypto/ssh and server_standalone
func main() {
var (
readOnly bool
debugStderr bool
)
flag.BoolVar(&readOnly, "R", false, "read-only server")
flag.BoolVar(&debugStderr, "e", false, "debug to stderr")
flag.Parse()
debugStream := ioutil.Discard
if debugStderr {
debugStream = os.Stderr
}
// An SSH server is represented by a ServerConfig, which holds
// certificate details and handles authentication of ServerConns.
config := &ssh.ServerConfig{
PasswordCallback: func(c ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
// Should use constant-time compare (or better, salt+hash) in
// a production setting.
fmt.Fprintf(debugStream, "Login: %s\n", c.User())
if c.User() == "testuser" && string(pass) == "tiger" {
return nil, nil
}
return nil, fmt.Errorf("password rejected for %q", c.User())
},
}
privateBytes, err := ioutil.ReadFile("id_rsa")
if err != nil {
log.Fatal("Failed to load private key", err)
}
private, err := ssh.ParsePrivateKey(privateBytes)
if err != nil {
log.Fatal("Failed to parse private key", err)
}
config.AddHostKey(private)
// Once a ServerConfig has been configured, connections can be
// accepted.
listener, err := net.Listen("tcp", "0.0.0.0:2022")
if err != nil {
log.Fatal("failed to listen for connection", err)
}
fmt.Printf("Listening on %v\n", listener.Addr())
nConn, err := listener.Accept()
if err != nil {
log.Fatal("failed to accept incoming connection", err)
}
// Before use, a handshake must be performed on the incoming
// net.Conn.
_, chans, reqs, err := ssh.NewServerConn(nConn, config)
if err != nil {
log.Fatal("failed to handshake", err)
}
fmt.Fprintf(debugStream, "SSH server established\n")
// The incoming Request channel must be serviced.
go ssh.DiscardRequests(reqs)
// Service the incoming Channel channel.
for newChannel := range chans {
// Channels have a type, depending on the application level
// protocol intended. In the case of an SFTP session, this is "subsystem"
// with a payload string of "<length=4>sftp"
fmt.Fprintf(debugStream, "Incoming channel: %s\n", newChannel.ChannelType())
if newChannel.ChannelType() != "session" {
newChannel.Reject(ssh.UnknownChannelType, "unknown channel type")
fmt.Fprintf(debugStream, "Unknown channel type: %s\n", newChannel.ChannelType())
continue
}
channel, requests, err := newChannel.Accept()
if err != nil {
log.Fatal("could not accept channel.", err)
}
fmt.Fprintf(debugStream, "Channel accepted\n")
// Sessions have out-of-band requests such as "shell",
// "pty-req" and "env". Here we handle only the
// "subsystem" request.
go func(in <-chan *ssh.Request) {
for req := range in {
fmt.Fprintf(debugStream, "Request: %v\n", req.Type)
ok := false
switch req.Type {
case "subsystem":
fmt.Fprintf(debugStream, "Subsystem: %s\n", req.Payload[4:])
if string(req.Payload[4:]) == "sftp" {
ok = true
}
}
fmt.Fprintf(debugStream, " - accepted: %v\n", ok)
req.Reply(ok, nil)
}
}(requests)
serverOptions := []sftp.ServerOption{
sftp.WithDebug(debugStream),
}
if readOnly {
serverOptions = append(serverOptions, sftp.ReadOnly())
fmt.Fprintf(debugStream, "Read-only server\n")
} else {
fmt.Fprintf(debugStream, "Read write server\n")
}
server, err := sftp.NewServer(
channel,
serverOptions...,
)
if err != nil {
log.Fatal(err)
}
if err := server.Serve(); err == io.EOF {
server.Close()
log.Print("sftp client exited session.")
} else if err != nil {
log.Fatal("sftp server completed with error:", err)
}
}
}
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