ssh2-sftp-client
Advanced tools
The ssh2-sftp-client npm package is a promise-based SFTP client for Node.js, built on top of the ssh2 module. It provides a simple and easy-to-use interface for performing various SFTP operations such as uploading, downloading, listing, and deleting files on a remote server.
Connecting to an SFTP server
This feature allows you to establish a connection to an SFTP server using the provided host, port, username, and password.
const Client = require('ssh2-sftp-client');
const sftp = new Client();
sftp.connect({
host: 'example.com',
port: '22',
username: 'username',
password: 'password'
}).then(() => {
console.log('Connected');
}).catch(err => {
console.error(err.message);
});Uploading a file
This feature allows you to upload a file from your local system to the remote SFTP server.
sftp.put('local/path/to/file.txt', 'remote/path/to/file.txt').then(() => {
console.log('File uploaded');
}).catch(err => {
console.error(err.message);
});Downloading a file
This feature allows you to download a file from the remote SFTP server to your local system.
sftp.get('remote/path/to/file.txt', 'local/path/to/file.txt').then(() => {
console.log('File downloaded');
}).catch(err => {
console.error(err.message);
});Listing files in a directory
This feature allows you to list all files and directories in a specified remote directory.
sftp.list('remote/path/to/directory').then(data => {
console.log(data);
}).catch(err => {
console.error(err.message);
});Deleting a file
This feature allows you to delete a specified file from the remote SFTP server.
sftp.delete('remote/path/to/file.txt').then(() => {
console.log('File deleted');
}).catch(err => {
console.error(err.message);
});The ssh2 package is a general-purpose SSH2 client and server module for Node.js. It provides a lower-level API compared to ssh2-sftp-client, allowing for more granular control over SSH and SFTP operations. However, it requires more boilerplate code to accomplish the same tasks.
The node-sftp package is another SFTP client for Node.js. It offers similar functionalities to ssh2-sftp-client but is less popular and has fewer features. It is also not as actively maintained as ssh2-sftp-client.
The scp2 package is a client for SCP (Secure Copy Protocol) in Node.js. While it provides functionalities for transferring files over SSH, it is limited to SCP and does not support the full range of SFTP operations that ssh2-sftp-client does.
an SFTP client for node.js, a wrapper around SSH2 which provides a high level convenience abstraction as well as a Promise based API.
Documentation on the methods and available options in the underlying modules can be found on the SSH2 project pages.
Current stable release is v7.0.0.
Code has been tested against Node versions 12.22.1, 14.17.0 and 16.2.0
Node versions < 10.x are not supported.
npm install ssh2-sftp-client
let Client = require('ssh2-sftp-client');
let sftp = new Client();
sftp.connect({
host: '127.0.0.1',
port: '8080',
username: 'username',
password: '******'
}).then(() => {
return sftp.list('/pathname');
}).then(data => {
console.log(data, 'the data info');
}).catch(err => {
console.log(err, 'catch error');
});
This version is based on version 1.1.0 of ssh2. This version of ssh2 is a complete re-write of the ssh2 library. This re-write addresses issues encountered when using node v14 as well as some design weaknesses in the previous 0.8.x version.
Breaking Change Expanded option handling for get() and put() methods. A number of use cases were identified where setting specific options on the read and write streams and the pipe operation are necessary. For example, disabling autoClose on streams or the end event in pipes. The options argument for get() and put() calls now supports properties for readStreamOptions, writeStreamOptions and pipeOptions. Note that options are only applied to streams created by the get() and put() methods. Streams passed into these methods are under the control of the client code and therefore cannot have options supplied in arguments to those streams (you would apply such options when you create the streams). Options are typically only necessary in special use cases. Most of the time, no options are required. However, if you are currently using options to either put() or get(), you will need to update your code to map these options to the new structure.
Improved event handling. A listener for a global error event is now defined to catch errors which occur in-between method calls i.e. connection lost in-between calls to the library methods. A new mechanism has also been added for removal of listeners when no longer required.
The connection options are the same as those offered by the underlying SSH2 module. For full details, please see SSH2 client methods
All the methods will return a Promise, except for on() and removeListener(), which are typically only used in special use cases.
The convention with both FTP and SFTP is that paths are specified using a 'nix' style i.e. use / as the path separator. This means that even if your SFTP server is running on a win32 platform, you should use / instead of \ as the path separator. For example, for a win32 path of C:\Users\fred you would actually use /C:/Users/fred. If your win32 server does not support the 'nix' path convention, you can try setting the remotePathSep property of the SftpClient object to the path separator of your remote server. This might work, but has not been tested. Please let me know if you need to do this and provide details of the SFTP server so that I can try to create an appropriate environment and adjust things as necessary. At this point, I'm not aware of any win32 based SFTP servers which do not support the 'nix' path convention.
All remote paths must either be absolute e.g. /absolute/path/to/file or they can be relative with a prefix of either ./ (relative to current remote directory) or ../ (relative to parent of current remote directory) e.g. ./relative/path/to/file or ../relative/to/parent/file. It is also possible to do things like ../../../file to specify the parent of the parent of the parent of the current remote directory. The shell tilde (~) and common environment variables like $HOME are NOT supported.
It is important to recognise that the current remote directory may not always be what you may expect. A lot will depend on the remote platform of the SFTP server and how the SFTP server has been configured. When things don't seem to be working as expected, it is often a good idea to verify your assumptions regarding the remote directory and remote paths. One way to do this is to login using a command line program like sftp or lftp.
There is a small performance hit for using ./ and ../ as the module must query the remote server to determine what the root path is and derive the absolute path. Using absolute paths are therefore more efficient and likely more robust.
When specifying file paths, ensure to include a full path i.e. include the remote filename. Don't expect the module to append the local file name to the path you provide. For example, the following will not work
client.put('/home/fred/test.txt', '/remote/dir');
will not result in the file test.txt being copied to /remote/dir/test.txt. You need to specify the target filename as well e.g.
client.put('/home/fred/test.txt', '/remote/dir/test.txt');
Note that the remote file name does not have to be the same as the local file name. The following works fine;
client.put('/home/fred/test.txt', '/remote/dir/test-copy.txt');
This will copy the local file test.txt to the remote file test-copy.txt in the directory /remote/dir.
Constructor to create a new ssh2-sftp-client object. An optional name string can be provided, which will be used in error messages to help identify which client has thrown the error.
Constructor Arguments
Example Use
'use strict';
const Client = require('ssh2-sftp-client');
const config = {
host: 'example.com',
username: 'donald',
password: 'my-secret'
};
const sftp = new Client('example-client');
sftp.connect(config)
.then(() => {
return sftp.cwd();
})
.then(p => {
console.log(`Remote working directory is ${p}`);
return sftp.end();
})
.catch(err => {
console.log(`Error: ${err.message}`); // error message will include 'example-client'
});
Connect to an sftp server. Full documentation for connection options is available here
Connection Options
This module is based on the excellent SSH2 module. That module is a general SSH2 client and server library and provides much more functionality than just SFTP connectivity. Many of the connect options provided by that module are less relevant for SFTP connections. It is recommended you keep the config options to the minimum needed and stick to the options listed in the commonOpts below.
The retries, retry_factor and retry_minTimeout options are not part of the SSH2 module. These are part of the configuration for the retry package and what is used to enable retrying of sftp connection attempts. See the documentation for that package for an explanation of these values.
// common options
let commonOpts {
host: 'localhost', // string Hostname or IP of server.
port: 22, // Port number of the server.
forceIPv4: false, // boolean (optional) Only connect via IPv4 address
forceIPv6: false, // boolean (optional) Only connect via IPv6 address
username: 'donald', // string Username for authentication.
password: 'borsch', // string Password for password-based user authentication
agent: process.env.SSH_AGENT, // string - Path to ssh-agent's UNIX socket
privateKey: fs.readFileSync('/path/to/key'), // Buffer or string that contains
passphrase: 'a pass phrase', // string - For an encrypted private key
readyTimeout: 20000, // integer How long (in ms) to wait for the SSH handshake
strictVendor: true // boolean - Performs a strict server vendor check
debug: myDebug // function - Set this to a function that receives a single
// string argument to get detailed (local) debug information.
retries: 2 // integer. Number of times to retry connecting
retry_factor: 2 // integer. Time factor used to calculate time between retries
retry_minTimeout: 2000 // integer. Minimum timeout between attempts
};
// rarely used options
let advancedOpts {
localAddress,
localPort,
hostHash,
hostVerifier,
agentForward,
localHostname,
localUsername,
tryKeyboard,
authHandler,
keepaliveInterval,
keepaliveCountMax,
sock,
algorithms,
compress
};
Example Use
sftp.connect({
host: example.com,
port: 22,
username: 'donald',
password: 'youarefired'
});
Retrieves a directory listing. This method returns a Promise, which once realised, returns an array of objects representing items in the remote directory.
/.*/.Example Use
const Client = require('ssh2-sftp-client');
const config = {
host: 'example.com',
port: 22,
username: 'red-don',
password: 'my-secret'
};
let sftp = new Client;
sftp.connect(config)
.then(() => {
return sftp.list('/path/to/remote/dir');
})
.then(data => {
console.log(data);
})
.then(() => {
sftp.end();
})
.catch(err => {
console.error(err.message);
});
Return Objects
The objects in the array returned by list() have the following properties;
{
type: // file type(-, d, l)
name: // file name
size: // file size
modifyTime: // file timestamp of modified time
accessTime: // file timestamp of access time
rights: {
user:
group:
other:
},
owner: // user ID
group: // group ID
}
Pattern Filter
The filter options can be a regular expression (most powerful option) or a simple glob-like string where * will match any number of characters, e.g.
foo* => foo, foobar, foobaz
*bar => bar, foobar, tabbar
*oo* => foo, foobar, look, book
The glob-style matching is very simple. In most cases, you are best off using a real regular expression which will allow you to do more powerful matching and anchor matches to the beginning/end of the string etc.
Tests to see if remote file or directory exists. Returns type of remote object if it exists or false if it does not.
Example Use
const Client = require('ssh2-sftp-client');
const config = {
host: 'example.com',
port: 22,
username: 'red-don',
password: 'my-secret'
};
let sftp = new Client;
sftp.connect(config)
.then(() => {
return sftp.exists('/path/to/remote/dir');
})
.then(data => {
console.log(data); // will be false or d, -, l (dir, file or link)
})
.then(() => {
sftp.end();
})
.catch(err => {
console.error(err.message);
});
Returns the attributes associated with the object pointed to by path.
Attributes
The stat() method returns an object with the following properties;
let stats = {
mode: 33279, // integer representing type and permissions
uid: 1000, // user ID
gid: 985, // group ID
size: 5, // file size
accessTime: 1566868566000, // Last access time. milliseconds
modifyTime: 1566868566000, // last modify time. milliseconds
isDirectory: false, // true if object is a directory
isFile: true, // true if object is a file
isBlockDevice: false, // true if object is a block device
isCharacterDevice: false, // true if object is a character device
isSymbolicLink: false, // true if object is a symbolic link
isFIFO: false, // true if object is a FIFO
isSocket: false // true if object is a socket
};
Example Use
let client = new Client();
client.connect(config)
.then(() => {
return client.stat('/path/to/remote/file');
})
.then(data => {
// do something with data
})
.then(() => {
client.end();
})
.catch(err => {
console.error(err.message);
});
Retrieve a file from a remote SFTP server. The dst argument defines the destination and can be either a string, a stream object or undefined. If it is a string, it is interpreted as the path to a location on the local file system (path should include the file name). If it is a stream object, the remote data is passed to it via a call to pipe(). If dst is undefined, the method will put the data into a buffer and return that buffer when the Promise is resolved. If dst is defined, it is returned when the Promise is resolved.
In general, if your going to pass in a string as the destination, you are better off using the fastGet() method.
get() command (see below).Options
The options argument can be used to pass options to the underlying streams and pipe call used by this method. The argument is an object with three possible properties, readStreamOptions, writeStreamOptions and pipeOptions. The values for each of these properties should be an object containing the required options. For example, possible read stream and pipe options could be defined as
let options = {
readStreamOptions: {
flags: 'r',
encoding: null,
handle: null,
mode: 0o666,
autoClose: true
},
pipeOptions: {
end: false
}};
Most of the time, you won't want to use any options. Sometimes, it may be useful to set the encoding. For example, to 'utf-8'. However, it is important not to do this for binary files to avoid data corruption.
Example Use
let client = new Client();
let remotePath = '/remote/server/path/file.txt';
let dst = fs.createWriteStream('/local/file/path/copy.txt');
client.connect(config)
.then(() => {
return client.get(remotePath, dst);
})
.then(() => {
client.end();
})
.catch(err => {
console.error(err.message);
});
zlib.createGunzip() writeable stream, you can both download and decompress a gzip file 'on the fly'.Downloads a file at remotePath to localPath using parallel reads for faster throughput. This is the simplest method if you just want to download a file.
fastGet() (see below)Options
{
concurrency: 64, // integer. Number of concurrent reads to use
chunkSize: 32768, // integer. Size of each read in bytes
step: function(total_transferred, chunk, total) // callback called each time a
// chunk is transferred
}
Sample Use
let client = new Client();
let remotePath = '/server/path/file.txt';
let localPath = '/local/path/file.txt';
client.connect(config)
.then(() => {
client.fastGet(remotePath, localPath);
})
.then(() => {
client.end();
})
.catch(err => {
console.error(err.message);
});
Upload data from local system to remote server. If the src argument is a string, it is interpreted as a local file path to be used for the data to transfer. If the src argument is a buffer, the contents of the buffer are copied to the remote file and if it is a readable stream, the contents of that stream are piped to the remotePath on the server.
Options
The options object supports three properties, readStreamOptions, writeStreamOptions and pipeOptions. The value for each property should be an object with options as properties and their associated values representing the option value. For example, you might use the following to set writeStream options.
{
writeStreamOptions: {
flags: 'w', // w - write and a - append
encoding: null, // use null for binary files
mode: 0o666, // mode to use for created file (rwx)
autoClose: true // automatically close the write stream when finished
}}
The most common options to use are mode and encoding. The values shown above are the defaults. You do not have to set encoding to utf-8 for text files, null is fine for all file types. However, using utf-8 encoding for binary files will often result in data corruption.
Example Use
let client = new Client();
let data = fs.createReadStream('/path/to/local/file.txt');
let remote = '/path/to/remote/file.txt';
client.connect(config)
.then(() => {
return client.put(data, remote);
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
fastPut().Uploads the data in file at localPath to a new file on remote server at remotePath using concurrency. The options object allows tweaking of the fast put process.
Options
{
concurrency: 64, // integer. Number of concurrent reads
chunkSize: 32768, // integer. Size of each read in bytes
mode: 0o755, // mixed. Integer or string representing the file mode to set
step: function(total_transferred, chunk, total) // function. Called every time
// a part of a file was transferred
}
Example Use
let localFile = '/path/to/file.txt';
let remoteFile = '/path/to/remote/file.txt';
let client = new Client();
client.connect(config)
.then(() => {
client.fastPut(localFile, remoteFile);
})
.then(() => {
client.end();
})
.catch(err => {
console.error(err.message);
});
Append the input data to an existing remote file. There is no integrity checking performed apart from normal writeStream checks. This function simply opens a writeStream on the remote file in append mode and writes the data passed in to the file.
Options
The following options are supported;
{
flags: 'a', // w - write and a - append
encoding: null, // use null for binary files
mode: 0o666, // mode to use for created file (rwx)
autoClose: true // automatically close the write stream when finished
}
The most common options to use are mode and encoding. The values shown above are the defaults. You do not have to set encoding to utf-8 for text files, null is fine for all file types. Generally, I would not attempt to append binary files.
Example Use
let remotePath = '/path/to/remote/file.txt';
let client = new Client();
client.connect(config)
.then(() => {
return client.append(Buffer.from('Hello world'), remotePath);
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
Create a new directory. If the recursive flag is set to true, the method will create any directories in the path which do not already exist. Recursive flag defaults to false.
Example Use
let remoteDir = '/path/to/new/dir';
let client = new Client();
client.connect(config)
.then(() => {
return client.mkdir(remoteDir, true);
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
Remove a directory. If removing a directory and recursive flag is set to true, the specified directory and all sub-directories and files will be deleted. If set to false and the directory has sub-directories or files, the action will fail.
Note: There has been at least one report that some SFTP servers will allow non-empty directories to be removed even without the recursive flag being set to true. While this is not standard behaviour, it is recommended that users verify the behaviour of rmdir if there are plans to rely on the recursive flag to prevent removal of non-empty directories.
Example Use
let remoteDir = '/path/to/remote/dir';
let client = new Client();
client.connect(config)
.then(() => {
return client.rmdir(remoteDir, true);
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
Delete a file on the remote server.
path: string. Path to remote file to be deleted.
noErrorOK: boolean. If true, no error is raised when you try to delete a non-existent file. Default is false.
Example Use
let remoteFile = '/path/to/remote/file.txt';
let client = new Client();
client.connect(config)
.then(() => {
return client.delete(remoteFile);
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
Rename a file or directory from fromPath to toPath. You must have the necessary permissions to modify the remote file.
Example Use
let from = '/remote/path/to/old.txt';
let to = '/remote/path/to/new.txt';
let client = new Client();
client.connect(config)
.then(() => {
return client.rename(from, to);
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
This method uses the openssh POSIX rename extension introduced in OpenSSH 4.8. The advantage of this version of rename over standard SFTP rename is that it is an atomic operation and will allow renaming a resource where the destination name exists. The POSIX rename will also work on some filesystems which do not support standard SFTP rename because they don't support the system hardlink() call. The POSIX rename extension is available on all openSSH servers from 4.8 and some other implementations. This is an extension to the standard SFTP protocol and therefore is not supported on all sSFTP servers.
let from = '/remote/path/to/old.txt';
let to = '/remote/path/to/new.txt';
let client = new Client();
client.connect(config)
.then(() => {
return client.posixRename(from, to);
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
Change the mode (read, write or execute permissions) of a remote file or directory.
Example Use
let path = '/path/to/remote/file.txt';
let newMode = 0o644; // rw-r-r
let client = new Client();
client.connect(config)
.then(() => {
return client.chmod(path, newMode);
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
Converts a relative path to an absolute path on the remote server. This method is mainly used internally to resolve remote path names.
Warning: Currently, there is a platform inconsistency with this method on win32 platforms. For servers running on non-win32 platforms, providing a path which does not exist on the remote server will result in an empty e.g. '', absolute path being returned. On servers running on win32 platforms, a normalised path will be returned even if the path does not exist on the remote server. It is therefore advised not to use this method to also verify a path exists. instead, use the exist() method.
Returns what the server believes is the current remote working directory.
Upload the directory specified by srcDir to the remote directory specified by dstDir. The dstDir will be created if necessary. Any sub directories within srcDir will also be uploaded. Any existing files in the remote path will be overwritten.
The upload process also emits 'upload' events. These events are fired for each successfully uploaded file. The upload event calls listeners with 1 argument, an object which has properties source and destination. The source property is the path of the file uploaded and the destination property is the path to where the file was uploaded to. The purpose of this event is to provide some way for client code to get feedback on the upload progress. You can add your own lisener using the on() method.
The optionsl filter argument is a regular expression which can be used to select which files and directories to include in the upload.
Example
'use strict';
// Example of using the uploadDir() method to upload a directory
// to a remote SFTP server
const path = require('path');
const SftpClient = require('../src/index');
const dotenvPath = path.join(__dirname, '..', '.env');
require('dotenv').config({path: dotenvPath});
const config = {
host: process.env.SFTP_SERVER,
username: process.env.SFTP_USER,
password: process.env.SFTP_PASSWORD,
port: process.env.SFTP_PORT || 22
};
async function main() {
const client = new SftpClient('upload-test');
const src = path.join(__dirname, '..', 'test', 'testData', 'upload-src');
const dst = '/home/tim/upload-test';
try {
await client.connect(config);
client.on('upload', info => {
console.log(`Listener: Uploaded ${info.source}`);
});
let rslt = await client.uploadDir(src, dst);
return rslt;
} finally {
client.end();
}
}
main()
.then(msg => {
console.log(msg);
})
.catch(err => {
console.log(`main error: ${err.message}`);
});
Download the remote directory specified by srcDir to the local file system directory specified by dstDir. The dstDir directory will be created if required. All sub directories within srcDir will also be copied. Any existing files in the local path will be overwritten. No files in the local path will be deleted.
The method also emites download events to provide a way to monitor download progress. The download event listener is called with one argument, an object with two properties, source and destination. The source property is the path to the remote file that has been downloaded and the destination is the local path to where the file was downloaded to. You can add a listener for this event using the on() method.
The optional filter argument is a regular expression which can be used to select which files and directories will be downloaded from the remote server.
Example
'use strict';
// Example of using the downloadDir() method to upload a directory
// to a remote SFTP server
const path = require('path');
const SftpClient = require('../src/index');
const dotenvPath = path.join(__dirname, '..', '.env');
require('dotenv').config({path: dotenvPath});
const config = {
host: process.env.SFTP_SERVER,
username: process.env.SFTP_USER,
password: process.env.SFTP_PASSWORD,
port: process.env.SFTP_PORT || 22
};
async function main() {
const client = new SftpClient('upload-test');
const dst = '/tmp';
const src = '/home/tim/upload-test';
try {
await client.connect(config);
client.on('download', info => {
console.log(`Listener: Download ${info.source}`);
});
let rslt = await client.downloadDir(src, dst);
return rslt;
} finally {
client.end();
}
}
main()
.then(msg => {
console.log(msg);
})
.catch(err => {
console.log(`main error: ${err.message}`);
});
Ends the current client session, releasing the client socket and associated resources. This function also removes all listeners associated with the client.
Example Use
let client = new Client();
client.connect(config)
.then(() => {
// do some sftp stuff
})
.then(() => {
return client.end();
})
.catch(err => {
console.error(err.message);
});
Although normally not required, you can add and remove custom listeners on the ssh2 client object. This object supports a number of events, but only a few of them have any meaning in the context of SFTP. These are
on(eventType, listener)
Adds the specified listener to the specified event type. It the event type is error, the listener should accept 1 argument, which will be an Error object. The event handlers for end and close events have no arguments.
The handlers will be added to the beginning of the listener's event handlers, so it will be called before any of the ssh2-sftp-client listeners.
removeListener(eventType, listener)
Removes the specified listener from the event specified in eventType. Note that the end() method automatically removes all listeners from the client object.
All SFTP servers and platforms are not equal. Some facilities provided by ssh2-sftp-client either depend on capabilities of the remote server or the underlying capabilities of the remote server platform. As an example, consider chmod(). This command depends on a remote filesystem which implements the 'nix' concept of users and groups. The win32 platform does not have the same concept of users and groups, so chmod() will not behave in the same way.
One way to determine whether an issue you are encountering is due to ssh2-sftp-client or due to the remote server or server platform is to use a simple CLI sftp program, such as openSSH's sftp command. If you observe the same behaviour using plain sftp on the command line, the issue is likely due to server or remote platform limitations. Note that you should not use a GUI sftp client, like Filezilla or winSCP as such GUI programs often attempt to hide these server and platform incompatibilities and will take additional steps to simulate missing functionality etc. You want to use a CLI program which does as little as possible.
One of the challenges in providing a Promise based API over a module like SSH2, which is event based is how to ensure events are handled appropriately. The challenge is due to the synchronous nature of events. You cannot use try/catch for events because you have no way of knowing when the event might fire. For example, it could easily fire after your try/catch block as completed execution.
Things become even more complicated once you mix in Promises. When you define a promise, you have to methods which can be called to fulfil a promise, resolve and reject. Only one can be called - once you call resolve, you cannot call reject (well, you can call it, but it won't have any impact on the fulfilment status of the promise). The problem arises when an event, for exmaple an error event is fired either after you have resolved a promise or possibly in-between promises. If you don't catch the error event, your script will likely crash with an uncaught exception error.
To make matters worse, some servers, particularly servers running on a Windows platform, will raise multiple errors for the same error event. For example, when you attempt to connect with a bad username or password, you will get a All authentication methods have failed exception. However, under Windows, you will also get a Connection reset by peer exception. If we reject the connect promise based on the authentication failure exception, what do we do with the reset by peer exception? More critically, what will handle that exception given the promise has already been fulfilled and completed? To make matters worse, it seems that Windows based servers also raise an error event for non-errors. For example, when you call the end() method, the connection is closed. On windows, this also results in a connection reset by peer error. While it could be argued that the remote server resetting the connection after receiving a disconnect request is not an error, it doesn't change the fact that one is raised and we need to somehow deal with it.
To handle this, ssh2-sftp-client implements a couple of strategies. Firstly, when you call one of the module's methods, it adds error, end and close event listeners which will call the reject moethod on the enclosing promise. It also keeps track of whether an error has been handled and if it has, it ignores any subsequent errors until the promise ends. Typically, the first error caught has the most relevant information and any subsequent error events are less critical or informative, so ignoring them has no negative impact. Provided one of the events is raised before the promise is fulfilled, these handlers will consume the event and deal with it appropriately.
In testing, it was found that in some situations, particularly during connect operations, subsequent errors fired with a small delay. This prevents the errors from being handled by the event handlers associated with the connect promise. To deal with this, a small 500ms delay has been added to the connect() method, which effectively delays the removal of the event handlers until all events have been caught.
The other area where additional events are fired is during the end() call. To deal with these events, the end() method setus up listeners which will simply ignore additional error, end and close events. It is assumed that once you have called end() you really only care about any main error which occurs and no longer care about other errors that may be raised as the connection is terminated.
In addition to the promise based event handlers, ssh2-sftp-client also implements global event handlers which will catch any error, end or close events. Essentially, these global handlers only reset the sftp property of the client object, effectively ensuring any subsequent calls are rejected and in the case of an error, send the error to the console.
While the above strategies appear to work for the majority of use cases, there are always going to be edge cases which require more flexible or powerful event handling. To support this, the on() and removeListener() methods are provided. Any event listener added using the on() method will be added at the beginning of the list of handlers for that event, ensuring it will be called before any global or promise local events. See the documentation for the on() method for details.
It appears that when the sftp server is running on Windows, a ECONNRESET error signal is raised when the end() method is called. Unfortunately, this signal is raised after a considerable delay. This means we cannot remove the error handler used in the end() promise as otherwise you will get an uncaught exception error. Leaving the handler in place, even though we will ignore this error, solves that issue, but unfortunately introduces a new problem. Because we are not removing the listener, if you re-use the client object for subsequent connections, an additional error handler will be added. If this happens more than 11 times, you will eventually see the Node warning about a possible memory leak. This is because node monitors the number of error handlers and if it sees more than 11 added to an object, it assumes there is a problem and generates the warning.
The best way to avoid this issue is to not re-use client objects. Always generate a new sftp client object for each new connection.
Due to an issue with ECONNRESET error signals when connecting to Windows based SFTP servers, it is not possible to remove the error handler in the end() method. This means that if you re-use the SftpClient object for multiple connections e.g. calling connect(), then end(), then connect() etc, you run the risk of multiple error handlers being added to the SftpClient object. After 11 handlers have been added, Node will generate a possible memory leak warning.
To avoid this problem, don't re-use SftpClient objects. Generate a new SftpClient object for each connection. You can perform multiple actions with a single connection e.g. upload multiple files, download multiple files etc, but after you have called end(), you should not try to re-use the object with a further connect() call. Create a new object instead.
Many SFTP servers have rate limiting protection which will drop connections once a limit has been reached. In particular, openSSH has the setting MaxStartups, which can be a tuple of the form max:drop:full where max is the maximum allowed unauthenticated connections, drop is a percentage value which specifies percentage of connections to be dropped once max connections has been reached and full is the number of connections at which point all subsequent connections will be dropped. e.g. 10:30:60 means allow up to 10 unauthenticated connections after which drop 30% of connection attempts until reaching 60 unauthenticated connections, at which time, drop all attempts.
Clients first make an unauthenticated connection to the SFTP server to begin negotiation of protocol settings (cipher, authentication method etc). If you are creating multiple connections in a script, it is easy to exceed the limit, resulting in some connections being dropped. As SSH2 only raises an 'end' event for these dropped connections, no error is detected. The ssh2-sftp-client now listens for end events during the connection process and if one is detected, will reject the connection promise.
One way to avoid this type of issue is to add a delay between connection attempts. It does not need to be a very long delay - just sufficient to permit the previous connection to be authenticated. In fact, the default setting for openSSH is 10:30:60, so you really just need to have enough delay to ensure that the 1st connection has completed authentication before the 11th connection is attempted.
If the dst argument passed to the get method is a writeable stream, the remote file will be piped into that writeable. If the writeable you pass in is a writeable stream created with fs.createWriteStream(), the data will be written to the file specified in the constructor call to createWriteStream().
The writeable stream can be any type of write stream. For example, the below code will convert all the characters in the remote file to upper case before it is saved to the local file system. This could just as easily be something like a gunzip stream from zlib, enabling you to decompress remote zipped files as you bring them across before saving to local file system.
'use strict';
// Example of using a writeable with get to retrieve a file.
// This code will read the remote file, convert all characters to upper case
// and then save it to a local file
const Client = require('../src/index.js');
const path = require('path');
const fs = require('fs');
const through = require('through2');
const config = {
host: 'arch-vbox',
port: 22,
username: 'tim',
password: 'xxxx'
};
const sftp = new Client();
const remoteDir = '/home/tim/testServer';
function toupper() {
return through(function(buf, enc, next) {
next(null, buf.toString().toUpperCase());
});
}
sftp
.connect(config)
.then(() => {
return sftp.list(remoteDir);
})
.then(data => {
// list of files in testServer
console.dir(data);
let remoteFile = path.join(remoteDir, 'test.txt');
let upperWtr = toupper();
let fileWtr = fs.createWriteStream(path.join(__dirname, 'loud-text.txt'));
upperWtr.pipe(fileWtr);
return sftp.get(remoteFile, upperWtr);
})
.then(() => {
return sftp.end();
})
.catch(err => {
console.error(err.message);
});
There are a couple of ways to do this. Essentially, you want to setup SSH keys and use these for authentication to the remote server.
One solution, provided by @KalleVuorjoki is to use the SSH agent process. Note: SSHAUTHSOCK is normally created by your OS when you load the ssh-agent as part of the login session.
let sftp = new Client();
sftp.connect({
host: 'YOUR-HOST',
port: 'YOUR-PORT',
username: 'YOUR-USERNAME',
agent: process.env.SSH_AUTH_SOCK
}).then(() => {
sftp.fastPut(/* ... */)
}
Another alternative is to just pass in the SSH key directly as part of the configuration.
let sftp = new Client();
sftp.connect({
host: 'YOUR-HOST',
port: 'YOUR-PORT',
username: 'YOUR-USERNAME',
privateKey: fs.readFileSync('/path/to/ssh/key')
}).then(() => {
sftp.fastPut(/* ... */)
}
This solution was provided by @jmorino.
import { SocksClient } from 'socks';
import SFTPClient from 'ssh2-sftp-client';
const host = 'my-sftp-server.net';
const port = 22; // default SSH/SFTP port on remote server
// connect to SOCKS 5 proxy
const { socket } = await SocksClient.createConnection({
proxy: {
host: 'my.proxy', // proxy hostname
port: 1080, // proxy port
type: 5, // for SOCKS v5
},
command: 'connect',
destination: { host, port } // the remote SFTP server
});
const client = new SFTPClient();
client.connect({
host,
sock: socket, // pass the socket to proxy here (see ssh2 doc)
username: '.....',
privateKey: '.....'
})
// client is connected
Some users have encountered the error 'Timeout while waiting for handshake' or 'Handshake failed, no matching client->server ciphers. This is often due to the client not having the correct configuration for the transport layer algorithms used by ssh2. One of the connect options provided by the ssh2 module is algorithm, which is an object that allows you to explicitly set the key exchange, ciphers, hmac and compression algorithms as well as server host key used to establish the initial secure connection. See the SSH2 documentation for details. Getting these parameters correct usually resolves the issue.
If you want to limit the amount of bandwidth used during upload/download of data, you can use a stream to limit throughput. The following example was provided by kennylbj. Note that there is a caveat that we must set the autoClose flag to false to avoid calling an extra _read() on a closed stream that may cause _get Permission Denied error in ssh2-streams.
const Throttle = require('throttle');
const progress = require('progress-stream');
// limit download speed
const throttleStream = new Throttle(config.throttle);
// download progress stream
const progressStream = progress({
length: fileSize,
time: 500,
});
progressStream.on('progress', (progress) => {
console.log(progress.percentage.toFixed(2));
});
const outStream = createWriteStream(localPath);
// pipe streams together
throttleStream.pipe(progressStream).pipe(outStream);
try {
// set autoClose to false
await client.get(remotePath, throttleStream, { autoClose: false });
} catch (e) {
console.log('sftp error', e);
} finally {
await client.end();
}
I have started collecting example scripts in the example directory of the repository. These are mainly scripts I have put together in order to investigate issues or provide samples for users. They are not robust, lack adequate error handling and may contain errors. However, I think they are still useful for helping developers see how the module and API can be used.
The ssh2-sftp-client module is essentially a wrapper around the ssh2 and ssh2-streams modules, providing a higher level promise based API. When you run into issues, it is important to try and determine where the issue lies - either in the ssh2-sftp-client module or the underlying ssh2 and ssh2-streams modules. One way to do this is to first identify a minimal reproducible example which reproduces the issue. Once you have that, try to replicate the functionality just using the ssh2 and ssh2-streams modules. If the issue still occurs, then you can be fairly confident it is something related to those later 2 modules and therefore and issue which should be referred to the maintainer of that module.
The ssh2 and ssh2-streams modules are very solid, high quality modules with a large user base. Most of the time, issues with those modules are due to client misconfiguration. It is therefore very important when trying to diagnose an issue to also check the documentation for both ssh2 and ssh2-streams. While these modules have good defaults, the flexibility of the ssh2 protocol means that not all options are available by default. You may need to tweak the connection options, ssh2 algorithms and ciphers etc for some remote servers. The documentation for both the ssh2 and ssh2-streams module is quite comprehensive and there is lots of valuable information in the issue logs.
If you run into an issue which is not repeatable with just the ssh2 and ssh2-streams modules, then please log an issue against the ssh2-sftp-client module and I will investigate. Please note the next section on logging issues.
Note also that in the repository there are two useful directories. The first is the examples directory, which contain some examples of using ssh2-sftp-client to perform common tasks. A few minutes reviewing these examples can provide that additional bit of detail to help fix any problems you are encountering.
The second directory is the validation directory. I have some very simple scripts in this directory which perform basic tasks using only the ssh2 modules (no ssh2-sftp-client module). These can be useful when trying to determine if the issue is with the underlying ssh2 module or the ssh2-sftp-client wrapper module.
There are some common errors people tend to make when using Promises or Asyc/Await. These are by far the most common problem found in issues logged against this module. Please check for some of these before logging your issue.
then() blockAll methods in ssh2-sftp-client return a Promise. This means methods are executed asynchrnously. When you call a method inside the then() block of a promise chain, it is critical that you return the Promise that call generates. Failing to do this will result in the then() block completing and your code starting execution of the next then(), catch() or finally() block before your promise has been fulfilled. For example, the following will not do what you expect
sftp.connect(config)
.then(() => {
sftp.fastGet('foo.txt', 'bar.txt');
}).then(rslt => {
console.log(rslt);
sftp.end();
}).catch(e => {
console.error(e.message);
});
In the above code, the sftp.end() method will almost certainly be called before sftp.fastGet() has been fulfilled (unless the foo.txt file is really small!). In fact, the whole promise chain will complete and exit even before the sftp.end() call has been fulfilled. The correct code would be something like
sftp.connect(config)
.then(() => {
return sftp.fastGet('foo.txt', 'bar.txt');
}).then(rslt => {
console.log(rslt);
return sftp.end();
}).catch(e => {
console.error(e.message);
});
Note the return statements. These ensure that the Promise returned by the client method is returned into the promise chain. It will be this promise the next block in the chain will wait on to be fulfilled before the next block is executed. Without the return statement, that block will return the default promise for that block, which essentially says this block has been fulfilled. What you really want is the promise which says your sftp client method call has been fulfilled.
A common symptom of this type of error is for file uploads or download to fail to complete or for data in those files to be truncated. What is happening is that the connection is being ended before the transfer has completed.
Another common error is to mix Promise chains and async/await calls. This is rarely a great idea. While you can do this, it tends to create complicated and difficult to maintain code. Select one approach and stick with it. Both approaches are functionally equivalent, so there is no reason to mix up the two paradigms. My personal preference would be to use async/await as I think that is more natural for most developers. For example, the following is more complex and difficult to follow than necessary (and has a bug!)
sftp.connect(config)
.then(() => {
return sftp.cwd();
}).then(async (d) => {
console.log(`Remote directory is ${d}`);
try {
await sftp.fastGet(`${d}/foo.txt`, `./bar.txt`);
}.catch(e => {
console.error(e.message);
});
}).catch(e => {
console.error(e.message);
}).finally(() => {
sftp.end();
});
The main bug in the above code is the then() block is not returning the Promise generated by the call to sftp.fastGet(). What it is actually returning is a fulfilled promise which says the then() block has been run (note that the await'ed promise is not being returned and is therefore outside the main Promise chain). As a result, the finally() block will be executed before the await promise has been fulfilled.
Using async/await inside the promise chain has created unnecessary complexity and leads to incorrect assumptions regarding how the code will execute. A quick glance at the code is likely to give the impression that execution will wait for the sftp.fastGet() call to be fulfilled before continuing. This is not the case. The code would be more clearly expressed as either
sftp.connect(config)
.then(() => {
return sftp.cwd();
}).then(d => {
console.log(`remote dir ${d}`);
return sftp.fastGet(`${d}/foot.txt`, 'bar.txt');
}).catch(e => {
console.error(e.message);
}).finally(() => {
return sftp.end();
});
or, using async/await
async function doSftp() {
try {
let sftp = await sftp.connect(conf);
let d = await sftp.cwd();
console.log(`remote dir is ${d}`);
await sftp.fastGet(`${d}/foo.txt`, 'bat.txt');
} catch (e) {
console.error(e.message);
} finally () {
await sftp.end();
}
}
Another common error is to try and use a try/catch block to catch event signals, such as an error event. In general, you cannot use try/catch blocks for asynchronous code and expect errors to be caught by the catch block. Handling errors in asynchronous code is one of the key reasons we now have the Promise and async/await frameworks.
The basic problem is that the try/catch block will have completed execution before the asynchronous code has completed. If the asynchronous code has not compleed, then there is a potential for it to raise an error. However, as the try/catch block has already completed, there is no catch waiting to catch the error. It will bubble up and probably result in your script exiting with an uncaught exception error.
Error events are essentially asynchronous code. You don't know when such events will fire. Therefore, you cannot use a try/catch block to catch such event errors. Even creating an error handler which then throws an exception won't help as the key problem is that your try/catch block has already executed. There are a number of alternative ways to deal with this situation. However, the key symptom is that you see occasional uncaught error exceptions that cause your script to exit abnormally despite having try/catch blocks in your script. What you need to do is look at your code and find where errors are raised asynchronously and use an event handler or some other mechanism to manage any errors raised.
Not all SFTP servers are the same. Like most standards, the SFTP protocol has some level of interpretation and allows different levels of compliance. This means there can be differences in behaviour between different servers and code which works with one server will not work the same with another. For example, the value returned by realpath for non-existent objects can differ significantly. Some servers will throw an error for a particular operation while others will just return null, some servers support concurrent operations (such as used by fastGet/fastPut) while others will not and of course, the text of error messages can vary significantly. In particular, we have noticed significant differences across different platforms. It is therefore advisable to do comprehensive testing when the SFTP server is moved to a new platform. This includes moving from to a cloud based service even if the underlying platform remains the same. I have noticed that some cloud platforms can generate unexpected events, possibly related to additional functionality or features associated with the cloud implementation. For example, it appears SFTP servers running under Azure will generate an error event when the connection is closed even when the client has requested the connection be terminated. The same SFTP server running natively on Windows does not appear to exhibit such behaviour.
Technically, SFTP should be able to perform multiple operations concurrently. As node is single threaded, what we a really talking about is running multiple execution contexts as a pool where node will switch contexts when each context is blocked due to things like waiting on network data etc. However, I have found this to be extremely unreliable and of very little benefit from a performance perspective. My recommendation is to therefore avoid executing multiple requests over the same connection in parallel (for example, generating multiple get() promises and using something like Promise.all() to resolve them.
If you are going to try and perform concurrent operations, you need to test extensively and ensure you are using data which is large enough that context switching does occur (i.e. the request is not completed in a single run). Some SFTP servers will handle concurrent operations better than others.
You can add a debug property to the config object passed in to connect() to turn on debugging. This will generate quite a lot of output. The value of the property should be a function which accepts a single string argument. For example;
config.debug = msg => {
console.error(msg);
};
Enabling debugging can generate a lot of output. If you use console.error() as the output (as in the example above), you can redirect the output to a file using shell redirection e.g.
node script.js 2> debug.log
If you just want to see debug messages from ssh2-sftp-client and exclude debug messages from the underlying ssh2 and ssh2-streams modules, you can filter based on messages which start with 'CLIENT' e.g.
{
debug: (msg) => {
if (msg.startsWith('CLIENT')) {
console.error(msg);
}
}
}
Please log an issue for all bugs, questions, feature and enhancement requests. Please ensure you include the module version, node version and platform.
I am happy to try and help diagnose and fix any issues you encounter while using the ssh2-sftp-client module. However, I will only put in effort if you are prepared to put in the effort to provide the information necessary to reproduce the issue. Things which will help
Perhaps the best assistance is a minimal reproducible example of the issue. Once the issue can be readily reproduced, it can usually be fixed very quickly.
Pull requests are always welcomed. However, please ensure your changes pass all tests and if your adding a new feature, that tests for that feature are included. Likewise, for new features or enhancements, please include any relevant documentation updates.
This module will adopt a standard semantic versioning policy. Please indicate in your pull request what level of change it represents i.e.
This module was initially written by jyu213. On August 23rd, 2019, theophilusx took over responsibility for maintaining this module. A number of other people have contributed to this module, but until now, this was not tracked. My intention is to credit anyone who contributes going forward.
Thanks to the following for their contributions -
FAQs
ssh2 sftp client for node
The npm package ssh2-sftp-client receives a total of 507,923 weekly downloads. As such, ssh2-sftp-client popularity was classified as popular.
We found that ssh2-sftp-client demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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