chore: Handle sftp reconnections

.build-tools/go.mod

@@ -1,6 +1,8 @@
 module github.com/dapr/components-contrib/build-tools
 
-go 1.24.4
+go 1.24.6
+
+toolchain go1.24.10
 
 require (
 	github.com/dapr/components-contrib v0.0.0

bindings/sftp/client.go

@@ -0,0 +1,255 @@
+/*
+Copyright 2025 The Dapr Authors
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package sftp
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"sync"
+	"sync/atomic"
+
+	sftpClient "github.com/pkg/sftp"
+	"golang.org/x/crypto/ssh"
+
+	"github.com/dapr/kit/logger"
+)
+
+type Client struct {
+	sshClient      *ssh.Client
+	sftpClient     *sftpClient.Client
+	address        string
+	config         *ssh.ClientConfig
+	lock           sync.RWMutex
+	needsReconnect atomic.Bool
+	log            logger.Logger
+}
+
+func newClient(address string, config *ssh.ClientConfig, log logger.Logger) (*Client, error) {
+	if address == "" || config == nil {
+		return nil, errors.New("sftp binding error: client not initialized")
+	}
+
+	sshClient, err := newSSHClient(address, config)
+	if err != nil {
+		return nil, err
+	}
+
+	newSftpClient, err := sftpClient.NewClient(sshClient)
+	if err != nil {
+		_ = sshClient.Close()
+		return nil, fmt.Errorf("sftp binding error: error create sftp client: %w", err)
+	}
+
+	return &Client{
+		sshClient:  sshClient,
+		sftpClient: newSftpClient,
+		address:    address,
+		config:     config,
+		log:        log,
+	}, nil
+}
+
+func (c *Client) Close() error {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	// Close SFTP first, then SSH
+	var sftpErr, sshErr error
+	if c.sftpClient != nil {
+		sftpErr = c.sftpClient.Close()
+	}
+	if c.sshClient != nil {
+		sshErr = c.sshClient.Close()
+	}
+
+	// Return the first error encountered
+	if sftpErr != nil {
+		return sftpErr
+	}
+	return sshErr
+}
+
+func (c *Client) list(path string) ([]os.FileInfo, error) {
+	var fi []os.FileInfo
+
+	fn := func() error {
+		var err error
+		fi, err = c.sftpClient.ReadDir(path)
+		return err
+	}
+
+	err := c.withReconnection(fn)
+	if err != nil {
+		return nil, err
+	}
+
+	return fi, nil
+}
+
+func (c *Client) create(path string) (*sftpClient.File, string, error) {
+	dir, fileName := sftpClient.Split(path)
+
+	var file *sftpClient.File
+
+	createFn := func() error {
+		cErr := c.sftpClient.MkdirAll(dir)
+		if cErr != nil {
+			return cErr
+		}
+
+		file, cErr = c.sftpClient.Create(path)
+		if cErr != nil {
+			return cErr
+		}
+
+		return nil
+	}
+
+	rErr := c.withReconnection(createFn)
+	if rErr != nil {
+		return nil, "", rErr
+	}
+
+	return file, fileName, nil
+}
+
+func (c *Client) get(path string) (*sftpClient.File, error) {
+	var f *sftpClient.File
+
+	fn := func() error {
+		var err error
+		f, err = c.sftpClient.Open(path)
+		return err
+	}
+
+	err := c.withReconnection(fn)
+	if err != nil {
+		return nil, err
+	}
+
+	return f, nil
+}
+
+func (c *Client) delete(path string) error {
+	fn := func() error {
+		return c.sftpClient.Remove(path)
+	}
+
+	err := c.withReconnection(fn)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (c *Client) ping() error {
+	_, err := c.sftpClient.Getwd()
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
+func (c *Client) withReconnection(fn func() error) error {
+	err := c.do(fn)
+	if !c.shouldReconnect(err) {
+		return err
+	}
+
+	c.log.Debugf("sftp binding error: %s", err)
+	c.needsReconnect.Store(true)
+
+	rErr := c.doReconnect()
+	if rErr != nil {
+		c.log.Debugf("sftp binding error: reconnect failed: %s", rErr)
+		return errors.Join(err, rErr)
+	}
+	c.log.Debugf("sftp binding: reconnected to %s", c.address)
+
+	c.log.Debugf("sftp binding: retrying operation")
+	return c.do(fn)
+}
+
+func (c *Client) do(fn func() error) error {
+	c.lock.RLock()
+	defer c.lock.RUnlock()
+	return fn()
+}
+
+func (c *Client) doReconnect() error {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+
+	c.log.Debugf("sftp binding: reconnecting to %s", c.address)
+
+	if !c.needsReconnect.Load() {
+		return nil
+	}
+
+	pErr := c.ping()
+	if pErr == nil {
+		c.needsReconnect.Store(false)
+		return nil
+	}
+
+	sshClient, err := newSSHClient(c.address, c.config)
+	if err != nil {
+		return err
+	}
+
+	newSftpClient, err := sftpClient.NewClient(sshClient)
+	if err != nil {
+		_ = sshClient.Close()
+		return fmt.Errorf("sftp binding error: error create sftp client: %w", err)
+	}
+
+	if c.sftpClient != nil {
+		_ = c.sftpClient.Close()
+	}
+	if c.sshClient != nil {
+		_ = c.sshClient.Close()
+	}
+
+	c.sftpClient = newSftpClient
+	c.sshClient = sshClient
+
+	c.needsReconnect.Store(false)
+	return nil
+}
+
+func newSSHClient(address string, config *ssh.ClientConfig) (*ssh.Client, error) {
+	sshClient, err := ssh.Dial("tcp", address, config)
+	if err != nil {
+		return nil, fmt.Errorf("sftp binding error: error dialing ssh server: %w", err)
+	}
+	return sshClient, nil
+}
+
+// shouldReconnect returns true if the error looks like a transport-level failure
+func (c *Client) shouldReconnect(err error) bool {
+	if err == nil {
+		return false
+	}
+
+	// SFTP status errors that are logical, not connectivity (avoid reconnect)
+	if errors.Is(err, sftpClient.ErrSSHFxPermissionDenied) ||
+		errors.Is(err, sftpClient.ErrSSHFxNoSuchFile) ||
+		errors.Is(err, sftpClient.ErrSSHFxOpUnsupported) {
+		return false
+	}
+
+	return true
+}

bindings/sftp/docker-compose.yaml

@@ -0,0 +1,11 @@
+services:
+  sftp:
+    image:
+      atmoz/sftp
+    environment:
+      - SFTP_USERS=foo:pass:1001:1001:upload
+    volumes:
+      - ./upload:/home/foo/upload
+    ports:
+      - "2222:22"
+

bindings/sftp/sftp.go

@@ -1,3 +1,16 @@
+/*
+Copyright 2025 The Dapr Authors
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+    http://www.apache.org/licenses/LICENSE-2.0
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
 package sftp
 
 import (
@@ -25,9 +38,9 @@ const (
 
 // Sftp is a binding for file operations on sftp server.
 type Sftp struct {
-	metadata   *sftpMetadata
-	logger     logger.Logger
-	sftpClient *sftpClient.Client
+	metadata *sftpMetadata
+	logger   logger.Logger
+	c        *Client
 }
 
 // sftpMetadata defines the sftp metadata.
@@ -115,19 +128,12 @@ func (sftp *Sftp) Init(_ context.Context, metadata bindings.Metadata) error {
 		HostKeyCallback: hostKeyCallback,
 	}
 
-	sshClient, err := ssh.Dial("tcp", m.Address, config)
-	if err != nil {
-		return fmt.Errorf("sftp binding error: error create ssh client: %w", err)
-	}
-
-	newSftpClient, err := sftpClient.NewClient(sshClient)
+	sftp.metadata = m
+	sftp.c, err = newClient(m.Address, config, sftp.logger)
 	if err != nil {
-		return fmt.Errorf("sftp binding error: error create sftp client: %w", err)
+		return fmt.Errorf("sftp binding error: create sftp client error: %w", err)
 	}
 
-	sftp.metadata = m
-	sftp.sftpClient = newSftpClient
-
 	return nil
 }
 
@@ -161,14 +167,9 @@ func (sftp *Sftp) create(_ context.Context, req *bindings.InvokeRequest) (*bindi
 		return nil, fmt.Errorf("sftp binding error: %w", err)
 	}
 
-	dir, fileName := sftpClient.Split(path)
+	c := sftp.c
 
-	err = sftp.sftpClient.MkdirAll(dir)
-	if err != nil {
-		return nil, fmt.Errorf("sftp binding error: error create dir %s: %w", dir, err)
-	}
-
-	file, err := sftp.sftpClient.Create(path)
+	file, fileName, err := c.create(path)
 	if err != nil {
 		return nil, fmt.Errorf("sftp binding error: error create file %s: %w", path, err)
 	}
@@ -211,7 +212,9 @@ func (sftp *Sftp) list(_ context.Context, req *bindings.InvokeRequest) (*binding
 		return nil, fmt.Errorf("sftp binding error: %w", err)
 	}
 
-	files, err := sftp.sftpClient.ReadDir(path)
+	c := sftp.c
+
+	files, err := c.list(path)
 	if err != nil {
 		return nil, fmt.Errorf("sftp binding error: error read dir %s: %w", path, err)
 	}
@@ -246,7 +249,9 @@ func (sftp *Sftp) get(_ context.Context, req *bindings.InvokeRequest) (*bindings
 		return nil, fmt.Errorf("sftp binding error: %w", err)
 	}
 
-	file, err := sftp.sftpClient.Open(path)
+	c := sftp.c
+
+	file, err := c.get(path)
 	if err != nil {
 		return nil, fmt.Errorf("sftp binding error: error open file %s: %w", path, err)
 	}
@@ -272,7 +277,9 @@ func (sftp *Sftp) delete(_ context.Context, req *bindings.InvokeRequest) (*bindi
 		return nil, fmt.Errorf("sftp binding error: %w", err)
 	}
 
-	err = sftp.sftpClient.Remove(path)
+	c := sftp.c
+
+	err = c.delete(path)
 	if err != nil {
 		return nil, fmt.Errorf("sftp binding error: error remove file %s: %w", path, err)
 	}
@@ -296,7 +303,7 @@ func (sftp *Sftp) Invoke(ctx context.Context, req *bindings.InvokeRequest) (*bin
 }
 
 func (sftp *Sftp) Close() error {
-	return sftp.sftpClient.Close()
+	return sftp.c.Close()
 }
 
 func (metadata sftpMetadata) getPath(requestMetadata map[string]string) (path string, err error) {