implement basic handy-sshd

2025-06-07 14:43:05 +00:00 · 2023-08-09 08:01:01 +09:00 · 2023-08-09 08:01:01 +09:00 · 101f99e80e
commit 101f99e80e
parent fbdc66d85a
15 changed files with 754 additions and 0 deletions
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@ -0,0 +1,12 @@
+version: 2
+updates:
+- package-ecosystem: gomod
+  directory: "/"
+  schedule:
+    interval: daily
+    timezone: Asia/Tokyo
+  open-pull-requests-limit: 99
+  reviewers:
+  - nwtgck
+  assignees:
+  - nwtgck
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@ -0,0 +1,31 @@
+name: CI
+
+on: [push]
+
+jobs:
+  build_multi_platform:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Go 1.x
+        uses: actions/setup-go@v2
+        with:
+          go-version: "1.20"
+      - name: Build for multi-platform
+        run: |
+          set -xeu
+          DIST=dist
+          mkdir $DIST
+          # (from: https://www.digitalocean.com/community/tutorials/how-to-build-go-executables-for-multiple-platforms-on-ubuntu-16-04)
+          platforms=("linux/amd64" "darwin/amd64" "linux/arm" "windows/amd64")
+          for platform in "${platforms[@]}"
+          do
+              platform_split=(${platform//\// })
+              export GOOS=${platform_split[0]}
+              export GOARCH=${platform_split[1]}
+              [ $GOOS = "windows" ] && EXTENSION='.exe' || EXTENSION=''
+              BUILD_PATH=handy-sshd-$GOOS-$GOARCH
+              mkdir $BUILD_PATH
+              # Build
+              CGO_ENABLED=0 go build -o "${BUILD_PATH}/handy-sshd${EXTENSION}" main/main.go
+          done
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@ -0,0 +1,25 @@
+name: goreleaser
+
+on:
+  push:
+    tags:
+      - '*'
+
+jobs:
+  goreleaser:
+    runs-on: ubuntu-20.04
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+      - name: Set up Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: "1.20"
+      - name: Run GoReleaser
+        uses: goreleaser/goreleaser-action@v2
+        with:
+          version: v1.3.1
+          args: release --rm-dist
+        env:
+          GITHUB_TOKEN: ${{ secrets.GH_PAT }}
--- a/.goreleaser.yml
+++ b/.goreleaser.yml
@ -0,0 +1,49 @@
+project_name: handy-sshd
+builds:
+  - env:
+      - CGO_ENABLED=0
+    goos:
+      - linux
+      - windows
+      - darwin
+      - freebsd
+    goarch:
+      - amd64
+      - arm
+      - arm64
+      - 386
+      - ppc64le
+      - s390x
+      - mips64
+      - mips64le
+    goarm:
+      - 6
+      - 7
+    main: ./main/main.go
+archives:
+  - name_template: '{{ .ProjectName }}-{{ .Version }}-{{ .Os }}-{{ .Arch }}{{ if .Arm }}v{{ .Arm }}{{ end }}{{ if .Mips }}-{{ .Mips }}{{ end }}'
+    format_overrides:
+      - goos: windows
+        format: zip
+nfpms:
+  - license: MIT
+    maintainer: Ryo Ota <nwtgck@nwtgck.org>
+    homepage: https://github.com/nwtgck/handy-sshd
+    description: "Portable SSH server"
+    formats:
+      - rpm
+      - deb
+    file_name_template: '{{ .ProjectName }}-{{ .Version }}-{{ .Os }}-{{ .Arch }}{{ if .Arm }}v{{ .Arm }}{{ end }}{{ if .Mips }}-{{ .Mips }}{{ end }}'
+checksum:
+  name_template: 'checksums.txt'
+release:
+  github:
+  disable: false
+  prerelease: auto
+  name_template: "v{{.Version}}"
+brews:
+  - tap:
+      owner: nwtgck
+      name: homebrew-handy-sshd
+    homepage: "https://github.com/nwtgck/handy-sshd"
+    description: "Portable SSH server"
--- a/21
+++ b/21
@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2021 Ryo Ota
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
--- a/README.md
+++ b/README.md
@ -0,0 +1,2 @@
+# handy-sshd
+Portable SSH Server 
--- a/cmd/key.go
+++ b/cmd/key.go
@ -0,0 +1,28 @@
+package cmd
+
+const defaultHostKeyPem = `-----BEGIN RSA PRIVATE KEY-----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+-----END RSA PRIVATE KEY-----
+`
--- a/cmd/root.go
+++ b/cmd/root.go
@ -0,0 +1,117 @@
+package cmd
+
+import (
+	"fmt"
+	"github.com/nwtgck/handy-sshd"
+	"github.com/nwtgck/handy-sshd/version"
+	"github.com/spf13/cobra"
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/exp/slog"
+	"net"
+	"os"
+	"strconv"
+	"strings"
+)
+
+var flag struct {
+	//dnsServer    string
+	showsVersion bool
+	sshHost      string
+	sshPort      uint16
+	sshShell     string
+	sshUsers     []string
+}
+
+type sshUser struct {
+	name     string
+	password string
+}
+
+func init() {
+	cobra.OnInitialize()
+	RootCmd.PersistentFlags().BoolVarP(&flag.showsVersion, "version", "v", false, "show version")
+	RootCmd.PersistentFlags().StringVarP(&flag.sshHost, "host", "", "", "SSH server host (e.g. 127.0.0.1)")
+	RootCmd.PersistentFlags().Uint16VarP(&flag.sshPort, "port", "p", 2222, "SSH server port")
+	RootCmd.PersistentFlags().StringVarP(&flag.sshShell, "shell", "", "", "Shell")
+	//RootCmd.PersistentFlags().StringVar(&flag.dnsServer, "dns-server", "", "DNS server (e.g. 1.1.1.1:53)")
+	RootCmd.PersistentFlags().StringArrayVarP(&flag.sshUsers, "user", "", nil, `SSH user name (e.g. "john:mypassword")`)
+}
+
+var RootCmd = &cobra.Command{
+	Use:          os.Args[0],
+	Short:        "handy-sshd",
+	Long:         "Portable SSH server",
+	SilenceUsage: true,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		if flag.showsVersion {
+			fmt.Println(version.Version)
+			return nil
+		}
+		logger := slog.Default()
+		sshServer := &handy_sshd.Server{
+			Logger: logger,
+		}
+		var sshUsers []sshUser
+		for _, u := range flag.sshUsers {
+			splits := strings.SplitN(u, ":", 2)
+			if len(splits) != 2 {
+				return fmt.Errorf("invalid user format: %s", u)
+			}
+			sshUsers = append(sshUsers, sshUser{name: splits[0], password: splits[1]})
+		}
+
+		// (base: https://gist.github.com/jpillora/b480fde82bff51a06238)
+		sshConfig := &ssh.ServerConfig{
+			//Define a function to run when a client attempts a password login
+			PasswordCallback: func(metadata ssh.ConnMetadata, pass []byte) (*ssh.Permissions, error) {
+				for _, user := range sshUsers {
+					// No auth required
+					if user.name == metadata.User() && user.password == string(pass) {
+						return nil, nil
+					}
+				}
+				return nil, fmt.Errorf("password rejected for %q", metadata.User())
+			},
+			NoClientAuth: true,
+			NoClientAuthCallback: func(metadata ssh.ConnMetadata) (*ssh.Permissions, error) {
+				for _, user := range sshUsers {
+					// No auth required
+					if user.name == metadata.User() && user.password == "" {
+						return nil, nil
+					}
+				}
+				return nil, fmt.Errorf("%s auth required", metadata.User())
+			},
+		}
+		// TODO: specify priv_key by flags
+		pri, err := ssh.ParsePrivateKey([]byte(defaultHostKeyPem))
+		if err != nil {
+			return err
+		}
+		sshConfig.AddHostKey(pri)
+
+		// TODO: unix socket support
+		address := net.JoinHostPort(flag.sshHost, strconv.Itoa(int(flag.sshPort)))
+		ln, err := net.Listen("tcp", address)
+		if err != nil {
+			return err
+		}
+		logger.Info(fmt.Sprintf("listening on %s...", address))
+		for {
+			conn, err := ln.Accept()
+			if err != nil {
+				logger.Error("failed to accept TCP connection", "err", err)
+				continue
+			}
+			sshConn, chans, reqs, err := ssh.NewServerConn(conn, sshConfig)
+			if err != nil {
+				logger.Info("failed to handshake", "err", err)
+				conn.Close()
+				continue
+			}
+			logger.Info("new SSH connection", "client_version", string(sshConn.ClientVersion()))
+			go sshServer.HandleGlobalRequests(sshConn, reqs)
+			go sshServer.HandleChannels(flag.sshShell, chans)
+		}
+	},
+}
--- a/go.mod
+++ b/go.mod
@ -0,0 +1,21 @@
+module github.com/nwtgck/handy-sshd
+
+go 1.20
+
+require (
+	github.com/creack/pty v1.1.18
+	github.com/mattn/go-shellwords v1.0.12
+	github.com/pkg/errors v0.9.1
+	github.com/pkg/sftp v1.13.5
+	github.com/spf13/cobra v1.7.0
+	golang.org/x/crypto v0.12.0
+	golang.org/x/exp v0.0.0-20230807204917-050eac23e9de
+)
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/kr/fs v0.1.0 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/stretchr/testify v1.8.4 // indirect
+	golang.org/x/sys v0.11.0 // indirect
+)
--- a/go.sum
+++ b/go.sum
@ -0,0 +1,46 @@
+github.com/cpuguy83/go-md2man/v2 v2.0.2/go.mod h1:tgQtvFlXSQOSOSIRvRPT7W67SCa46tRHOmNcaadrF8o=
+github.com/creack/pty v1.1.18 h1:n56/Zwd5o6whRC5PMGretI4IdRLlmBXYNjScPaBgsbY=
+github.com/creack/pty v1.1.18/go.mod h1:MOBLtS5ELjhRRrroQr9kyvTxUAFNvYEK993ew/Vr4O4=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/inconshreveable/mousetrap v1.1.0 h1:wN+x4NVGpMsO7ErUn/mUI3vEoE6Jt13X2s0bqwp9tc8=
+github.com/inconshreveable/mousetrap v1.1.0/go.mod h1:vpF70FUmC8bwa3OWnCshd2FqLfsEA9PFc4w1p2J65bw=
+github.com/kr/fs v0.1.0 h1:Jskdu9ieNAYnjxsi0LbQp1ulIKZV1LAFgK1tWhpZgl8=
+github.com/kr/fs v0.1.0/go.mod h1:FFnZGqtBN9Gxj7eW1uZ42v5BccTP0vu6NEaFoC2HwRg=
+github.com/mattn/go-shellwords v1.0.12 h1:M2zGm7EW6UQJvDeQxo4T51eKPurbeFbe8WtebGE2xrk=
+github.com/mattn/go-shellwords v1.0.12/go.mod h1:EZzvwXDESEeg03EKmM+RmDnNOPKG4lLtQsUlTZDWQ8Y=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pkg/sftp v1.13.5 h1:a3RLUqkyjYRtBTZJZ1VRrKbN3zhuPLlUc3sphVz81go=
+github.com/pkg/sftp v1.13.5/go.mod h1:wHDZ0IZX6JcBYRK1TH9bcVq8G7TLpVHYIGJRFnmPfxg=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/russross/blackfriday/v2 v2.1.0/go.mod h1:+Rmxgy9KzJVeS9/2gXHxylqXiyQDYRxCVz55jmeOWTM=
+github.com/spf13/cobra v1.7.0 h1:hyqWnYt1ZQShIddO5kBpj3vu05/++x6tJ6dg8EC572I=
+github.com/spf13/cobra v1.7.0/go.mod h1:uLxZILRyS/50WlhOIKD7W6V5bgeIt+4sICxh6uRMrb0=
+github.com/spf13/pflag v1.0.5 h1:iy+VFUOCP1a+8yFto/drg2CJ5u0yRoB7fZw3DKv/JXA=
+github.com/spf13/pflag v1.0.5/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=
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+golang.org/x/crypto v0.12.0 h1:tFM/ta59kqch6LlvYnPa0yx5a83cL2nHflFhYKvv9Yk=
+golang.org/x/crypto v0.12.0/go.mod h1:NF0Gs7EO5K4qLn+Ylc+fih8BSTeIjAP05siRnAh98yw=
+golang.org/x/exp v0.0.0-20230807204917-050eac23e9de h1:l5Za6utMv/HsBWWqzt4S8X17j+kt1uVETUX5UFhn2rE=
+golang.org/x/exp v0.0.0-20230807204917-050eac23e9de/go.mod h1:FXUEEKJgO7OQYeo8N01OfiKP8RXMtf6e8aTskBGqWdc=
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+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
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+golang.org/x/sys v0.11.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/term v0.11.0 h1:F9tnn/DA/Im8nCwm+fX+1/eBwi4qFjRT++MhtVC4ZX0=
+golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
--- a/main/main.go
+++ b/main/main.go
@ -0,0 +1,14 @@
+package main
+
+import (
+	"fmt"
+	"github.com/nwtgck/handy-sshd/cmd"
+	"os"
+)
+
+func main() {
+	if err := cmd.RootCmd.Execute(); err != nil {
+		_, _ = fmt.Fprintf(os.Stderr, err.Error())
+		os.Exit(-1)
+	}
+}
--- a/pty_related_unix.go
+++ b/pty_related_unix.go
@ -0,0 +1,66 @@
+//go:build !windows
+// +build !windows
+
+// NOTE: pty.Start() is not supported in Windows
+
+package handy_sshd
+
+import (
+	"github.com/creack/pty"
+	"github.com/pkg/errors"
+	"golang.org/x/crypto/ssh"
+	"io"
+	"os"
+	"os/exec"
+	"sync"
+)
+
+func (s *Server) createPty(shell string, connection ssh.Channel) (*os.File, error) {
+	if shell == "" {
+		shell = os.Getenv("SHELL")
+	}
+	if shell == "" {
+		shell = "sh"
+	}
+	// Fire up bash for this session
+	sh := exec.Command(shell)
+
+	// Prepare teardown function
+	closer := func() {
+		connection.SendRequest("exit-status", false, ssh.Marshal(exitStatusMsg{
+			Status: 0,
+		}))
+		connection.Close()
+		_, err := sh.Process.Wait()
+		if err != nil {
+			s.Logger.Info("failed to exit shell", err)
+		}
+		s.Logger.Info("session closed")
+	}
+
+	// Allocate a terminal for this channel
+	s.Logger.Info("creating pty...")
+	shf, err := pty.Start(sh)
+	if err != nil {
+		s.Logger.Info("failed to start pty", "err", err)
+		closer()
+		return nil, errors.Errorf("could not start pty (%s)", err)
+	}
+
+	// pipe session to bash and visa-versa
+	var once sync.Once
+	go func() {
+		io.Copy(connection, shf)
+		once.Do(closer)
+	}()
+	go func() {
+		io.Copy(shf, connection)
+		once.Do(closer)
+	}()
+	return shf, nil
+}
+
+// setWinsize sets the size of the given pty.
+func setWinsize(t *os.File, w, h uint32) error {
+	return pty.Setsize(t, &pty.Winsize{Rows: uint16(h), Cols: uint16(w)})
+}
--- a/pty_related_unsupported.go
+++ b/pty_related_unsupported.go
@ -0,0 +1,19 @@
+//go:build windows
+// +build windows
+
+package handy_sshd
+
+import (
+	"fmt"
+	"golang.org/x/crypto/ssh"
+	"os"
+)
+
+func (s *Server) createPty(shell string, connection ssh.Channel) (*os.File, error) {
+	return nil, fmt.Errorf("creation of pty unsupported")
+}
+
+// setWinsize sets the size of the given pty.
+func setWinsize(t *os.File, w, h uint32) error {
+	return fmt.Errorf("set-win-size unsupported")
+}
--- a/server.go
+++ b/server.go
@ -0,0 +1,300 @@
+// Copyright (c) 2021 Ryo Ota
+// Released under the MIT License
+
+// Copyright (c) 2020 Jaime Pillora <dev@jpillora.com>
+// Released under the MIT License
+// https://github.com/jpillora/sshd-lite/tree/master#mit-license
+
+package handy_sshd
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/x509"
+	"encoding/binary"
+	"encoding/pem"
+	"fmt"
+	"github.com/mattn/go-shellwords"
+	"github.com/pkg/sftp"
+	"golang.org/x/crypto/ssh"
+	"golang.org/x/exp/slog"
+	"io"
+	"net"
+	"os"
+	"os/exec"
+	"strconv"
+	"sync"
+)
+
+type Server struct {
+	Logger *slog.Logger
+	// TODO: DNS server ?
+}
+
+type exitStatusMsg struct {
+	Status uint32
+}
+
+func (s *Server) HandleChannels(shell string, chans <-chan ssh.NewChannel) {
+	// Service the incoming Channel channel in go routine
+	for newChannel := range chans {
+		go s.handleChannel(shell, newChannel)
+	}
+}
+
+func (s *Server) handleChannel(shell string, newChannel ssh.NewChannel) {
+	switch newChannel.ChannelType() {
+	case "session":
+		s.handleSession(shell, newChannel)
+	case "direct-tcpip":
+		s.handleDirectTcpip(newChannel)
+	default:
+		newChannel.Reject(ssh.UnknownChannelType, fmt.Sprintf("unknown channel type: %s", newChannel.ChannelType()))
+	}
+}
+
+func (s *Server) handleSession(shell string, newChannel ssh.NewChannel) {
+	// At this point, we have the opportunity to reject the client's
+	// request for another logical connection
+	connection, requests, err := newChannel.Accept()
+	if err != nil {
+		s.Logger.Info("Could not accept channel", "err", err)
+		return
+	}
+
+	var shf *os.File = nil
+
+	for req := range requests {
+		switch req.Type {
+		case "exec":
+			s.handleExecRequest(req, connection)
+		case "shell":
+			// We only accept the default shell
+			// (i.e. no command in the Payload)
+			if len(req.Payload) == 0 {
+				req.Reply(true, nil)
+			}
+		case "pty-req":
+			termLen := req.Payload[3]
+			w, h := parseDims(req.Payload[termLen+4:])
+			shf, err = s.createPty(shell, connection)
+			if err != nil {
+				req.Reply(false, nil)
+				return
+			}
+			setWinsize(shf, w, h)
+			// Responding true (OK) here will let the client
+			// know we have a pty ready for input
+			req.Reply(true, nil)
+		case "window-change":
+			w, h := parseDims(req.Payload)
+			if shf != nil {
+				setWinsize(shf, w, h)
+			}
+		case "subsystem":
+			s.handleSessionSubSystem(req, connection)
+		}
+	}
+}
+
+func (s *Server) handleExecRequest(req *ssh.Request, connection ssh.Channel) {
+	var msg struct {
+		Command string
+	}
+	if err := ssh.Unmarshal(req.Payload, &msg); err != nil {
+		s.Logger.Info("failed to parse message in exec", "err", err)
+		return
+	}
+	cmdSlice, err := shellwords.Parse(msg.Command)
+	if err != nil {
+		return
+	}
+	cmd := exec.Command(cmdSlice[0], cmdSlice[1:]...)
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return
+	}
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return
+	}
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		return
+	}
+	go io.Copy(stdin, connection)
+	go io.Copy(connection, stdout)
+	go io.Copy(connection, stderr)
+	req.Reply(true, nil)
+	var exitCode int
+	if err := cmd.Run(); err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			exitCode = exitErr.ExitCode()
+		}
+	}
+	connection.SendRequest("exit-status", false, ssh.Marshal(exitStatusMsg{
+		Status: uint32(exitCode),
+	}))
+	connection.Close()
+}
+
+func (s *Server) handleSessionSubSystem(req *ssh.Request, connection ssh.Channel) {
+	// https://github.com/pkg/sftp/blob/42e9800606febe03f9cdf1d1283719af4a5e6456/examples/go-sftp-server/main.go#L111
+	ok := string(req.Payload[4:]) == "sftp"
+	req.Reply(ok, nil)
+
+	serverOptions := []sftp.ServerOption{
+		sftp.WithDebug(os.Stderr),
+	}
+	sftpServer, err := sftp.NewServer(connection, serverOptions...)
+	if err != nil {
+		s.Logger.Info("failed to create sftp server", "err", err)
+		return
+	}
+	if err := sftpServer.Serve(); err == io.EOF {
+		sftpServer.Close()
+	} else if err != nil {
+		s.Logger.Info("failed to serve sftp server", "err", err)
+		return
+	}
+}
+
+// (base: https://github.com/peertechde/zodiac/blob/110fdd2dfd27359546c1cd75a9fec5de2882bf42/pkg/server/server.go#L228)
+func (s *Server) handleDirectTcpip(newChannel ssh.NewChannel) {
+	var msg struct {
+		RemoteAddr string
+		RemotePort uint32
+		SourceAddr string
+		SourcePort uint32
+	}
+	if err := ssh.Unmarshal(newChannel.ExtraData(), &msg); err != nil {
+		s.Logger.Info("failed to parse message", "err", err)
+		return
+	}
+	channel, reqs, err := newChannel.Accept()
+	if err != nil {
+		s.Logger.Info("failed to accept", "err", err)
+		return
+	}
+	go ssh.DiscardRequests(reqs)
+	raddr := net.JoinHostPort(msg.RemoteAddr, strconv.Itoa(int(msg.RemotePort)))
+	conn, err := net.Dial("tcp", raddr)
+	if err != nil {
+		s.Logger.Info("failed to dial", "err", err)
+		channel.Close()
+		return
+	}
+	var closeOnce sync.Once
+	closer := func() {
+		channel.Close()
+		conn.Close()
+	}
+	go func() {
+		io.Copy(channel, conn)
+		closeOnce.Do(closer)
+	}()
+	io.Copy(conn, channel)
+	closeOnce.Do(closer)
+	return
+}
+
+// =======================
+
+// parseDims extracts terminal dimensions (width x height) from the provided buffer.
+func parseDims(b []byte) (uint32, uint32) {
+	w := binary.BigEndian.Uint32(b)
+	h := binary.BigEndian.Uint32(b[4:])
+	return w, h
+}
+
+// ======================
+
+func GenerateKey() ([]byte, error) {
+	var r io.Reader
+	r = rand.Reader
+	priv, err := rsa.GenerateKey(r, 2048)
+	if err != nil {
+		return nil, err
+	}
+	err = priv.Validate()
+	if err != nil {
+		return nil, err
+	}
+	b := x509.MarshalPKCS1PrivateKey(priv)
+	return pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: b}), nil
+}
+
+// Borrowed from https://github.com/creack/termios/blob/master/win/win.go
+
+// ======================================================================
+
+func (s *Server) HandleGlobalRequests(sshConn *ssh.ServerConn, reqs <-chan *ssh.Request) {
+	for req := range reqs {
+		switch req.Type {
+		case "tcpip-forward":
+			s.handleTcpipForward(sshConn, req)
+		default:
+			// discard
+			if req.WantReply {
+				req.Reply(false, nil)
+			}
+			s.Logger.Info("request discarded", "request_type", req.Type)
+		}
+	}
+}
+
+// https://datatracker.ietf.org/doc/html/rfc4254#section-7.1
+func (s *Server) handleTcpipForward(sshConn *ssh.ServerConn, req *ssh.Request) {
+	var msg struct {
+		Addr string
+		Port uint32
+	}
+	if err := ssh.Unmarshal(req.Payload, &msg); err != nil {
+		req.Reply(false, nil)
+		return
+	}
+	ln, err := net.Listen("tcp", net.JoinHostPort(msg.Addr, strconv.Itoa(int(msg.Port))))
+	if err != nil {
+		req.Reply(false, nil)
+		return
+	}
+	go func() {
+		sshConn.Wait()
+		ln.Close()
+		s.Logger.Info("connection closed", "address", ln.Addr().String())
+	}()
+	for {
+		conn, err := ln.Accept()
+		if err != nil {
+			return
+		}
+		var replyMsg struct {
+			Addr           string
+			Port           uint32
+			OriginatorAddr string
+			OriginatorPort uint32
+		}
+		replyMsg.Addr = msg.Addr
+		replyMsg.Port = msg.Port
+
+		go func() {
+			channel, reqs, err := sshConn.OpenChannel("forwarded-tcpip", ssh.Marshal(&replyMsg))
+			if err != nil {
+				req.Reply(false, nil)
+				conn.Close()
+				return
+			}
+			go ssh.DiscardRequests(reqs)
+			go func() {
+				io.Copy(channel, conn)
+				conn.Close()
+				channel.Close()
+			}()
+			go func() {
+				io.Copy(conn, channel)
+				conn.Close()
+				channel.Close()
+			}()
+		}()
+	}
+}
--- a/version/version.go
+++ b/version/version.go
@ -0,0 +1,3 @@
+package version
+
+const Version = "0.1.0-SNAPSHOT"