Ever wondered how to connect to a sftp directly from your typescript application?

Oct 2022 #sftp #typescript #tests

Nowadays, it's way more likely that you'll need to connect to Buckets on some cloud provider but sometimes (and it happened to me), you might find yourself with the need to connect to a sftp server directly. If this is your case too, I hope this article will be able to help you set that up with an awesome test coverage.

What should I do when I try to connect to a SFTP.

First thing first, you should try to avoid doing that. If possible, you can look into how to synchronize the SFTP to a Cloud Bucket. (For example, you can look into AWS)

Now If you're still here, it might mean that this is not a choice for you. Or you're just that curious to know how that would be done directly from your application. If so you're in luck so buckle up!

Chose a client library.

When trying to connect to a new protocol, picking up a good library is always a must. SSH2 seems like the best solution out there to handle ssh (and thus sftp) workflows. Unfortunately, it's a bit too low level for a casual use of a sftp server (you will need to look into if if you're looking to get crafty with your sftp server but then this article won't help you anymore :D)

That is why, I would direct you to ssh2-sftp-client. A simple wrapper that provide a usable promise API over ssh2.

Connect to your SFTP server

This is the easy part of all of this.

Let's start by getting our package.json in order

1npm install ssh2-sftp-client
2
3yarn add ssh2-sftp-client

And then in the place you need to connect to the sftp server just go with something along the line of

1import Client from "ssh2-sftp-client";
2
3const client = new Client();
4await client.connect({
5  host: "127.0.0.1", // You sftp server IP address
6  port: 9999, // You sftp server port
7  username: "test", // Your username
8  password: "test", // You can also opt in for private key authentication
9});

Once connected, you can do most operation that you'd like to using the client

1// Write "Content" in a file on the server
2await client.put(Buffer.from("Content"), "/directory/filename.extension");
3
4// Get back the content of the file
5const content = await client.get("/directory/filename.extension");
6
7// List all files in a directory
8const files = await client.list("/directory");

If you're not familiar with SFTP, you could give the ssh2 documentation to get an overview of the available commands here

Okay, so what's left?

If you're building a quick POC then you're all set but if you're trying to add this to an application, you're probably wondering how you're going to make your test suite run smoothly. If you're only doing unit tests, you can probably get away by mocking the client library but if you also want some integration/e2e tests, you might want to setup a sftp server to respond to your client calls.

I would argue that you have two main choices to do this

Look for a docker image of a sftp server, understand it's configuration and add it to both your local env and the CI setup.
Install and a library that I built specially for this -> sftp-mock-server

Set it up

1npm install --save-dev @micham/sftp-mock-server
2
3yarn add -D @micham/sftp-mock-server

See it in action

 1describe("MySFTPClient", () => {
 2  let mockServer: Server;
 3  beforeEach(async () => {
 4    mockServer = await createSftpMockServer({
 5      port: "9999",
 6      hostname: "127.0.0.1",
 7      debug: (msg: string) => logger.debug(msg),
 8    });
 9  });
10
11  afterEach(async () => {
12    await closeServer(mockServer);
13  });
14
15  it("should be able to write file to the SFTP server", () => {
16    // GIVEN
17    const client = new MySFTPClient();
18
19    // WHEN
20    const result = client.doMyThingUsingSftp();
21
22    // THEN check result
23  });
24});