ssh connection

go.mod

@@ -5,6 +5,7 @@ go 1.21.4
 require (
 	github.com/docker/docker v24.0.7+incompatible
 	github.com/docker/go-connections v0.4.0
+	github.com/function61/gokit v0.0.0-20231117065306-355fe206d542
 	github.com/go-playground/validator/v10 v10.16.0
 	github.com/kevinburke/ssh_config v1.2.0
 	github.com/mitchellh/mapstructure v1.5.0
@@ -13,7 +14,7 @@ require (
 	github.com/spf13/viper v1.17.0
 	go.uber.org/zap v1.26.0
 	golang.design/x/lockfree v0.0.1
-	golang.org/x/crypto v0.13.0
+	golang.org/x/crypto v0.14.0
 	google.golang.org/grpc v1.58.2
 	google.golang.org/protobuf v1.31.0
 )
@@ -49,8 +50,9 @@ require (
 	go.uber.org/multierr v1.11.0 // indirect
 	golang.org/x/exp v0.0.0-20230905200255-921286631fa9 // indirect
 	golang.org/x/mod v0.12.0 // indirect
-	golang.org/x/net v0.15.0 // indirect
+	golang.org/x/net v0.17.0 // indirect
-	golang.org/x/sys v0.12.0 // indirect
+	golang.org/x/sync v0.3.0 // indirect
+	golang.org/x/sys v0.13.0 // indirect
 	golang.org/x/text v0.13.0 // indirect
 	golang.org/x/tools v0.13.0 // indirect
 	google.golang.org/genproto/googleapis/rpc v0.0.0-20230920204549-e6e6cdab5c13 // indirect

go.sum

@@ -77,6 +77,8 @@ github.com/frankban/quicktest v1.14.4 h1:g2rn0vABPOOXmZUj+vbmUp0lPoXEMuhTpIluN0X
 github.com/frankban/quicktest v1.14.4/go.mod h1:4ptaffx2x8+WTWXmUCuVU6aPUX1/Mz7zb5vbUoiM6w0=
 github.com/fsnotify/fsnotify v1.6.0 h1:n+5WquG0fcWoWp6xPWfHdbskMCQaFnG6PfBrh1Ky4HY=
 github.com/fsnotify/fsnotify v1.6.0/go.mod h1:sl3t1tCWJFWoRz9R8WJCbQihKKwmorjAbSClcnxKAGw=
+github.com/function61/gokit v0.0.0-20231117065306-355fe206d542 h1:a9BTN+DOboRkVih0suT4zrRZ4zLGFpBtHPGNd+EQ4pI=
+github.com/function61/gokit v0.0.0-20231117065306-355fe206d542/go.mod h1:sJY957+7ush4oj4ElOMhUFaFIriAFNAGYzVh2tFJNy0=
 github.com/gabriel-vasile/mimetype v1.4.2 h1:w5qFW6JKBz9Y393Y4q372O9A7cUSequkh1Q7OhCmWKU=
 github.com/gabriel-vasile/mimetype v1.4.2/go.mod h1:zApsH/mKG4w07erKIaJPFiX0Tsq9BFQgN3qGY5GnNgA=
 github.com/go-gl/glfw v0.0.0-20190409004039-e6da0acd62b1/go.mod h1:vR7hzQXu2zJy9AVAgeJqvqgH9Q5CA+iKCZ2gyEVpxRU=
@@ -255,8 +257,8 @@ golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8U
 golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/crypto v0.0.0-20210421170649-83a5a9bb288b/go.mod h1:T9bdIzuCu7OtxOm1hfPfRQxPLYneinmdGuTeoZ9dtd4=
 golang.org/x/crypto v0.0.0-20220722155217-630584e8d5aa/go.mod h1:IxCIyHEi3zRg3s0A5j5BB6A9Jmi73HwBIUl50j+osU4=
-golang.org/x/crypto v0.13.0 h1:mvySKfSWJ+UKUii46M40LOvyWfN0s2U+46/jDd0e6Ck=
+golang.org/x/crypto v0.14.0 h1:wBqGXzWJW6m1XrIKlAH0Hs1JJ7+9KBwnIO8v66Q9cHc=
-golang.org/x/crypto v0.13.0/go.mod h1:y6Z2r+Rw4iayiXXAIxJIDAJ1zMW4yaTpebo8fPOliYc=
+golang.org/x/crypto v0.14.0/go.mod h1:MVFd36DqK4CsrnJYDkBA3VC4m2GkXAM0PvzMCn4JQf4=
 golang.org/x/exp v0.0.0-20190121172915-509febef88a4/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190306152737-a1d7652674e8/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/exp v0.0.0-20190510132918-efd6b22b2522/go.mod h1:ZjyILWgesfNpC6sMxTJOJm9Kp84zZh5NQWvqDGG3Qr8=
@@ -326,8 +328,8 @@ golang.org/x/net v0.0.0-20201209123823-ac852fbbde11/go.mod h1:m0MpNAwzfU5UDzcl9v
 golang.org/x/net v0.0.0-20201224014010-6772e930b67b/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20210226172049-e18ecbb05110/go.mod h1:m0MpNAwzfU5UDzcl9v0D8zg8gWTRqZa9RBIspLL5mdg=
 golang.org/x/net v0.0.0-20211112202133-69e39bad7dc2/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
-golang.org/x/net v0.15.0 h1:ugBLEUaxABaB5AJqW9enI0ACdci2RUd4eP51NTBvuJ8=
+golang.org/x/net v0.17.0 h1:pVaXccu2ozPjCXewfr1S7xza/zcXTity9cCdXQYSjIM=
-golang.org/x/net v0.15.0/go.mod h1:idbUs1IY1+zTqbi8yxTbhexhEEk5ur9LInksu6HrEpk=
+golang.org/x/net v0.17.0/go.mod h1:NxSsAGuq816PNPmqtQdLE42eU2Fs7NoRIZrHJAlaCOE=
 golang.org/x/oauth2 v0.0.0-20180821212333-d2e6202438be/go.mod h1:N/0e6XlmueqKjAGxoOufVs8QHGRruUQn6yWY3a++T0U=
 golang.org/x/oauth2 v0.0.0-20190226205417-e64efc72b421/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
 golang.org/x/oauth2 v0.0.0-20190604053449-0f29369cfe45/go.mod h1:gOpvHmFTYa4IltrdGE7lF6nIHvwfUNPOp7c8zoXwtLw=
@@ -385,11 +387,11 @@ golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20210423185535-09eb48e85fd7/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.0.0-20220908164124-27713097b956/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.12.0 h1:CM0HF96J0hcLAwsHPJZjfdNzs0gftsLfgKt57wWHJ0o=
+golang.org/x/sys v0.13.0 h1:Af8nKPmuFypiUBjVoU9V20FiaFXOcuZI21p0ycVYYGE=
-golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.13.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
-golang.org/x/term v0.12.0 h1:/ZfYdc3zq+q02Rv9vGqTeSItdzZTSNDmfTi0mBAuidU=
+golang.org/x/term v0.13.0 h1:bb+I9cTfFazGW51MZqBVmZy7+JEJMouUHTUSKVQLBek=
-golang.org/x/term v0.12.0/go.mod h1:owVbMEjm3cBLCHdkQu9b1opXd4ETQWc3BhuQGKgXgvU=
+golang.org/x/term v0.13.0/go.mod h1:LTmsnFJwVN6bCy1rVCoS+qHT1HhALEFxKncY3WNNh4U=
 golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.1-0.20180807135948-17ff2d5776d2/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=

internal/server/driver/ssh/driver.go

@@ -3,17 +3,14 @@ package ssh
 import (
 	"context"
 	"errors"
-	"fmt"
-	"os"
 	"path"
-	"strings"
 	"sync"
 
 	"github.com/Neur0toxine/sshpoke/internal/config"
 	"github.com/Neur0toxine/sshpoke/internal/server/driver/base"
+	"github.com/Neur0toxine/sshpoke/internal/server/driver/ssh/sshproto"
 	"github.com/Neur0toxine/sshpoke/internal/server/driver/ssh/types"
 	"github.com/Neur0toxine/sshpoke/internal/server/driver/util"
-	"github.com/Neur0toxine/sshpoke/internal/server/proto/sshtun"
 	"github.com/Neur0toxine/sshpoke/pkg/dto"
 	"golang.org/x/crypto/ssh"
 )
@@ -21,28 +18,20 @@ import (
 type SSH struct {
 	base.Base
 	params Params
-	sessions map[string]conn
+	proto  *sshproto.Client
-	keys     []ssh.Signer
 	wg     sync.WaitGroup
 }
 
-type conn struct {
-	container dto.Container
-	tun       *sshtun.Tunnel
-}
-
 func New(ctx context.Context, name string, params config.DriverParams) (base.Driver, error) {
 	drv := &SSH{
 		Base: base.New(ctx, name),
-		sessions: make(map[string]conn),
 	}
 	if err := util.UnmarshalParams(params, &drv.params); err != nil {
 		return nil, err
 	}
 	drv.populateFromSSHConfig()
-	if err := drv.parseKeys(); err != nil {
+	drv.proto = sshproto.New(drv.params.Address, drv.params.Auth.User, drv.authenticators(), drv.Log())
-		return nil, err
+	go drv.proto.Connect(drv.Context())
-	}
 	return drv, nil
 }
 
@@ -82,78 +71,34 @@ func (d *SSH) WaitForShutdown() {
 	d.wg.Wait()
 }
 
-func (d *SSH) parseKeys() error {
+func (d *SSH) authenticators() []ssh.AuthMethod {
-	if d.params.Auth.Type != types.AuthTypeKey {
+	auth := d.authenticator()
+	if auth == nil {
 		return nil
 	}
-	dir, err := d.params.Auth.Directory.Resolve(true)
+	return []ssh.AuthMethod{auth}
-	if err != nil {
-		return fmt.Errorf("cannot parse keys: %s", err)
-	}
-	if d.params.Auth.Keyfile != "" {
-		key, err := parseKey(path.Join(dir, d.params.Auth.Keyfile))
-		if err != nil {
-			return err
-		}
-		d.keys = []ssh.Signer{key}
-		return nil
-	}
-	entries, err := os.ReadDir(dir)
-	if err != nil {
-		return fmt.Errorf("cannot read key directory: %s", err)
-	}
-	keys := []ssh.Signer{}
-	for _, entry := range entries {
-		if entry.IsDir() {
-			d.Log().Debugf("skipping '%s' because it's a directory", entry.Name())
-			continue
-		}
-		info, err := entry.Info()
-		if err != nil {
-			d.Log().Debugf("skipping '%s' because stat failed: %s", entry.Name(), err)
-			continue
-		}
-		if strings.HasSuffix(entry.Name(), ".pub") {
-			d.Log().Debugf("skipping '%s' because it's probably a public key", entry.Name())
-			continue
-		}
-		if entry.Name() == "config" {
-			d.Log().Debugf("skipping '%s' because it's probably a ssh-config file", entry.Name())
-			continue
-		}
-		if entry.Name() == "known_hosts" {
-			d.Log().Debugf(
-				"skipping '%s' because it's probably a list of hosts generated by OpenSSH", entry.Name())
-			continue
-		}
-		// this file is too small to be a private key
-		if info.Size() < 256 {
-			d.Log().Debugf("skipping '%s' because the file is smaller than 256 bytes", entry.Name())
-			continue
-		}
-		key, err := parseKey(path.Join(dir, entry.Name()))
-		if err != nil {
-			d.Log().Debugf("skipping '%s' because it's probably not a key: %s", entry.Name(), err)
-			continue
-		}
-		d.Log().Debugf("loading key '%s', type: %s", entry.Name(), key.PublicKey().Type())
-		keys = append(keys, key)
-	}
-	if len(keys) == 0 {
-		return errors.New("no keys in the provided directory")
-	}
-	d.keys = keys
-	return nil
 }
 
-func parseKey(keyFile string) (ssh.Signer, error) {
+func (d *SSH) authenticator() ssh.AuthMethod {
-	keyData, err := os.ReadFile(keyFile)
+	switch d.params.Auth.Type {
+	case types.AuthTypePasswordless:
+		return sshproto.AuthPassword("")
+	case types.AuthTypePassword:
+		return sshproto.AuthPassword(d.params.Auth.Password)
+	case types.AuthTypeKey:
+		if d.params.Auth.Keyfile != "" {
+			keyAuth, err := sshproto.AuthKeyFile(
+				types.SmartPath(path.Join(d.params.Auth.Directory.String(), d.params.Auth.Keyfile)))
 			if err != nil {
-		return nil, err
+				return nil
 			}
-	key, err := ssh.ParsePrivateKey(keyData)
+			return keyAuth
+		}
+		dirAuth, err := sshproto.AuthKeyDir(d.params.Auth.Directory)
 		if err != nil {
-		return nil, err
+			return nil
 		}
-	return key, nil
+		return dirAuth
+	}
+	return nil
 }

internal/server/driver/ssh/sshproto/auth.go

@@ -0,0 +1,91 @@
+package sshproto
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path"
+	"strings"
+
+	"github.com/Neur0toxine/sshpoke/internal/server/driver/ssh/types"
+	"golang.org/x/crypto/ssh"
+)
+
+func AuthKeyFile(keyFile types.SmartPath) (ssh.AuthMethod, error) {
+	key, err := readKey(keyFile)
+	if err != nil {
+		return nil, err
+	}
+	return ssh.PublicKeys(key), nil
+}
+
+func AuthKeyDir(keyDir types.SmartPath) (ssh.AuthMethod, error) {
+	keys, err := readKeys(keyDir)
+	if err != nil {
+		return nil, err
+	}
+	return ssh.PublicKeys(keys...), nil
+}
+
+func AuthPassword(password string) ssh.AuthMethod {
+	return ssh.Password(password)
+}
+
+func readKeys(keyDir types.SmartPath) ([]ssh.Signer, error) {
+	dir, err := keyDir.Resolve(true)
+	if err != nil {
+		return nil, fmt.Errorf("cannot parse keys: %s", err)
+	}
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return nil, fmt.Errorf("cannot read key directory: %s", err)
+	}
+	keys := []ssh.Signer{}
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		info, err := entry.Info()
+		if err != nil {
+			continue
+		}
+		if strings.HasSuffix(entry.Name(), ".pub") {
+			continue
+		}
+		if entry.Name() == "config" {
+			continue
+		}
+		if entry.Name() == "known_hosts" {
+			continue
+		}
+		// this file is too small to be a private key
+		if info.Size() < 256 {
+			continue
+		}
+		key, err := readKey(types.SmartPath(path.Join(dir, entry.Name())))
+		if err != nil {
+			continue
+		}
+		keys = append(keys, key)
+	}
+	if len(keys) == 0 {
+		return nil, errors.New("no keys in the provided directory")
+	}
+	return keys, nil
+}
+
+func readKey(keyFile types.SmartPath) (ssh.Signer, error) {
+	fileName, err := keyFile.Resolve(false)
+	if err != nil {
+		return nil, err
+	}
+	keyData, err := os.ReadFile(fileName)
+	if err != nil {
+		return nil, err
+	}
+	key, err := ssh.ParsePrivateKey(keyData)
+	if err != nil {
+		return nil, err
+	}
+	return key, nil
+}

internal/server/driver/ssh/sshproto/config.go

@@ -0,0 +1,21 @@
+package sshproto
+
+import (
+	"bytes"
+	"os"
+
+	"github.com/Neur0toxine/sshpoke/internal/server/driver/ssh/types"
+	"github.com/kevinburke/ssh_config"
+)
+
+func parseSSHConfig(filePath types.SmartPath) (*ssh_config.Config, error) {
+	fileName, err := filePath.Resolve(false)
+	if err != nil {
+		return nil, err
+	}
+	file, err := os.ReadFile(fileName)
+	if err != nil {
+		return nil, err
+	}
+	return ssh_config.Decode(bytes.NewReader(file))
+}

internal/server/driver/ssh/sshproto/forward.go

@@ -0,0 +1,19 @@
+package sshproto
+
+import "fmt"
+
+type Forward struct {
+	// local service to be forwarded
+	Local Endpoint `json:"local"`
+	// remote forwarding port (on remote SSH server network)
+	Remote Endpoint `json:"remote"`
+}
+
+type Endpoint struct {
+	Host string `json:"host"`
+	Port int    `json:"port"`
+}
+
+func (endpoint *Endpoint) String() string {
+	return fmt.Sprintf("%s:%d", endpoint.Host, endpoint.Port)
+}

internal/server/driver/ssh/sshproto/ssh.go

@@ -0,0 +1,242 @@
+package sshproto
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"sync/atomic"
+	"time"
+
+	"github.com/Neur0toxine/sshpoke/pkg/errtools"
+	"github.com/function61/gokit/app/backoff"
+	"github.com/function61/gokit/io/bidipipe"
+	"go.uber.org/zap"
+	"golang.org/x/crypto/ssh"
+)
+
+type Client struct {
+	user        string
+	address     string
+	authMethods []ssh.AuthMethod
+	log         *zap.SugaredLogger
+	connected   atomic.Bool
+}
+
+func New(address, user string, auth []ssh.AuthMethod, log *zap.SugaredLogger) *Client {
+	return &Client{
+		address:     prepareAddress(address),
+		user:        user,
+		authMethods: auth,
+		log:         log.With(zap.String("sshServer", address)),
+	}
+}
+
+func prepareAddress(address string) string {
+	_, _, err := net.SplitHostPort(address)
+	if err != nil && errtools.IsPortMissingErr(err) {
+		return net.JoinHostPort(address, "22")
+	}
+	return address
+}
+
+func (c *Client) Connect(ctx context.Context) {
+	if c.connected.Load() {
+		return
+	}
+
+	defer c.connected.Store(false)
+	backoffTime := backoff.ExponentialWithCappedMax(100*time.Millisecond, 5*time.Second)
+	for {
+		c.connected.Store(true)
+		err := c.connect(ctx)
+		if err != nil {
+			c.log.Error("connect error:", err)
+		}
+
+		select {
+		case <-ctx.Done():
+			return
+		default:
+		}
+
+		time.Sleep(backoffTime())
+	}
+}
+
+// connect once to the SSH server. if the connection breaks, we return error and the caller
+// will try to re-connect
+func (c *Client) connect(ctx context.Context) error {
+	c.log.Debug("connecting")
+	sshConfig := &ssh.ClientConfig{
+		User:            c.user,
+		Auth:            c.authMethods,
+		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
+	}
+
+	var sshClient *ssh.Client
+	var errConnect error
+
+	sshClient, errConnect = dialSSH(ctx, c.address, sshConfig)
+	if errConnect != nil {
+		return errConnect
+	}
+
+	// always disconnect when function returns
+	defer sshClient.Close()
+	defer c.log.Debug("disconnecting")
+
+	c.log.Debug("connected")
+
+	<-ctx.Done()
+	return nil
+}
+
+// // connect once to the SSH server. if the connection breaks, we return error and the caller
+// // will try to re-connect
+// func connectToSshAndServe2(
+// 	ctx context.Context,
+// 	address string,
+// 	authConfig types.Auth,
+// 	auth ssh.AuthMethod,
+// 	log *zap.SugaredLogger,
+// ) error {
+// 	log = log.With(zap.String("sshServer", address))
+// 	log.Debug("connecting")
+// 	sshConfig := &ssh.ClientConfig{
+// 		User:            authConfig.User,
+// 		Auth:            []ssh.AuthMethod{auth},
+// 		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
+// 	}
+//
+// 	var sshClient *ssh.Client
+// 	var errConnect error
+//
+// 	sshClient, errConnect = dialSSH(ctx, address, sshConfig)
+// 	if errConnect != nil {
+// 		return errConnect
+// 	}
+//
+// 	// always disconnect when function returns
+// 	defer sshClient.Close()
+// 	defer log.Debug("disconnecting")
+//
+// 	log.Debug("connected")
+//
+// 	// each listener in reverseForwardOnePort() can return one error, so make sure channel
+// 	// has enough buffering so even if we return from here, the goroutines won't block trying
+// 	// to return an error
+// 	listenerStopped := make(chan error, len(conf.Forwards))
+//
+// 	for _, forward := range conf.Forwards {
+// 		// TODO: "if any fails, tear down all workers" -style error handling would be better
+// 		// handled with https://pkg.go.dev/golang.org/x/sync/errgroup?tab=doc
+// 		if err := reverseForwardOnePort(
+// 			forward,
+// 			sshClient,
+// 			listenerStopped,
+// 			makeLogger("reverseForwardOnePort"),
+// 			makeLogger,
+// 		); err != nil {
+// 			// closes SSH connection if even one forward Listen() fails
+// 			return err
+// 		}
+// 	}
+//
+// 	// we're connected and have succesfully started listening on all reverse forwards, wait
+// 	// for either user to ask us to stop or any of the listeners to error
+// 	select {
+// 	case <-ctx.Done(): // cancel requested
+// 		return nil
+// 	case listenerFirstErr := <-listenerStopped:
+// 		// one or more of the listeners encountered an error. react by closing the connection
+// 		// assumes all the other listeners failed too so no teardown necessary
+// 		select {
+// 		case <-ctx.Done(): // pretty much errors are to be expected if cancellation triggered
+// 			return nil
+// 		default:
+// 			return listenerFirstErr
+// 		}
+// 	}
+// }
+
+//	blocking flow: calls Listen() on the SSH connection, and if succeeds returns non-nil error
+//
+// nonblocking flow: if Accept() call fails, stops goroutine and returns error on ch listenerStopped
+func reverseForwardOnePort(
+	forward Forward,
+	sshClient *ssh.Client,
+	listenerStopped chan<- error,
+	log *zap.SugaredLogger,
+) error {
+	// reverse listen on remote server port
+	listener, err := sshClient.Listen("tcp", forward.Remote.String())
+	if err != nil {
+		return err
+	}
+
+	go func() {
+		defer listener.Close()
+		log.Debugf("forwarding %s -> %s", forward.Local.String(), forward.Remote.String())
+
+		// handle incoming connections on reverse forwarded tunnel
+		for {
+			client, err := listener.Accept()
+			if err != nil {
+				listenerStopped <- fmt.Errorf("error on Accept(): %w", err)
+				return
+			}
+
+			// handle the connection in another goroutine, so we can support multiple concurrent
+			// connections on the same port
+			go handleReverseForwardConn(client, forward, log)
+		}
+	}()
+
+	return nil
+}
+
+func handleReverseForwardConn(client net.Conn, forward Forward, log *zap.SugaredLogger) {
+	defer client.Close()
+
+	log.Debugf("%s connected", client.RemoteAddr())
+	defer log.Debug("closed")
+
+	remote, err := net.Dial("tcp", forward.Local.String())
+	if err != nil {
+		log.Errorf("dial INTO local service error: %s", err.Error())
+		return
+	}
+
+	// pipe data in both directions:
+	// - client => remote
+	// - remote => client
+	//
+	// - in effect, we act as a proxy between the reverse tunnel's client and locally-dialed
+	//   remote endpoint.
+	// - the "client" and "remote" strings we give Pipe() is just for error&log messages
+	// - this blocks until either of the parties' socket closes (or breaks)
+	if err := bidipipe.Pipe(
+		bidipipe.WithName("client", client),
+		bidipipe.WithName("remote", remote),
+	); err != nil {
+		log.Error(err)
+	}
+}
+
+func dialSSH(ctx context.Context, addr string, sshConfig *ssh.ClientConfig) (*ssh.Client, error) {
+	dialer := net.Dialer{
+		Timeout: 10 * time.Second,
+	}
+
+	conn, err := dialer.DialContext(ctx, "tcp", addr)
+	if err != nil {
+		return nil, err
+	}
+
+	clConn, newChan, reqChan, err := ssh.NewClientConn(conn, addr, sshConfig)
+	if err != nil {
+		return nil, err
+	}
+
+	return ssh.NewClient(clConn, newChan, reqChan), nil
+}

internal/server/driver/ssh/types/auth.go

@@ -62,6 +62,10 @@ func (k SmartPath) Resolve(shouldBeDirectory bool) (result string, err error) {
 	return
 }
 
+func (k SmartPath) String() string {
+	return string(k)
+}
+
 func (a Auth) Validate() error {
 	if a.Type == AuthTypePassword && a.Password == "" {
 		return fmt.Errorf("password must be provided for authentication type '%s'", AuthTypePassword)

pkg/errtools/IsPortMissingErr.go

@@ -0,0 +1,18 @@
+package errtools
+
+import (
+	"errors"
+	"strings"
+)
+
+func IsPortMissingErr(err error) bool {
+	for {
+		if err == nil {
+			return false
+		}
+		if strings.Contains(err.Error(), "missing port in address") {
+			return true
+		}
+		err = errors.Unwrap(err)
+	}
+}

pkg/plugin/client.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/Neur0toxine/sshpoke/pkg/convert"
 	"github.com/Neur0toxine/sshpoke/pkg/dto"
+	"github.com/Neur0toxine/sshpoke/pkg/errtools"
 	"github.com/Neur0toxine/sshpoke/pkg/plugin/pb"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/credentials/insecure"
@@ -57,12 +58,12 @@ func normalizeAddr(addr string) string {
 	if strings.HasPrefix(addr, "grpc://") {
 		addr = addr[7:]
 	}
-	host, port, err := net.SplitHostPort(addr)
+	_, _, err := net.SplitHostPort(addr)
-	if err != nil && err.Error() == "missing port in address" {
+	if err != nil && errtools.IsPortMissingErr(err) {
-		host, port, err = net.SplitHostPort(addr + ":" + strconv.Itoa(DefaultPort))
+		addr = net.JoinHostPort(addr, strconv.Itoa(DefaultPort))
 	}
 	if err != nil {
 		return ""
 	}
-	return host + ":" + port
+	return addr
 }