WebFund 2024F: Tutorial 1

In this tutorial you will be studying and extending two implementations of simplegrep, included below. grep is a standard UNIX utility for returning lines from a text file that match a given pattern.

First, with the sync version, try the following:

• Make the search pattern into a regular expression.
• Give it an additional argument that causes matched lines to be output to a new file. You'll need to use writeTextFileSync() from the Deno file system API. When finished, output "All done!" to the console.
• Make the output lines sorted in alphabetical order.

Then, do all of the above with the async version. Make sure to use writeTextFile(), not writeTextFileSync()!

You may find the following methods useful when working with arrays:push(), pop(), shift(), unshift(), and join().

Code

simplegrep_sync.js

Downloadable version.

if (Deno.args.length < 2) {
    console.error('Not enough parameters given. Try this: ' +
                  '"deno run --allow-read simplegrep_sync term filename.txt"'); 
    Deno.exit(1);
}

var searchterm = Deno.args[0];
var filename = Deno.args[1];

var rawContents = Deno.readTextFileSync(filename);
var lines = rawContents.split('\n');

for (var i = 0; i < lines.length; i++) {
    if (lines[i].indexOf(searchterm) > -1) {
        console.log(lines[i]);
    }
}

simplegrep_async.js

Downloadable version.

if (Deno.args.length < 2) {
    console.error('Not enough parameters given. Try this: ' +
                  '"deno run --allow-read  simplegrep_async term filename.txt"'); 
    Deno.exit(1);
}

const searchterm = Deno.args[0];
const filename = Deno.args[1];

const returnMatches = function(rawContents) {

    const lines = rawContents.split('\n');

    lines.forEach(function(theLine) {
        if (theLine.indexOf(searchterm) > -1) {
            console.log(theLine);
        }
    });
}

const readPromise = Deno.readTextFile(filename);
try {
    const rawContents = await readPromise;
    returnMatches(rawContents);
} catch (error) {
    console.error(`Error reading file: ${error.message}`);
    Deno.exit(1);
}

Getting Started with Deno and Openstack

For this class you will be using Deno and a web broswer. While these are both cross-platform, we can provide the most support for running these applications inside the class Ubuntu Openstack cloud instances.

To get going with OpenStack, follow the SCS guide to OpenStack. Inside the COMP2406 project, create your own instance, with the name of your instance being your Carleton username plus "-comp2406-1" (so, "janesmith-comp2406-1"). If you need no make another instance, increment the number. You should normally have only one instance running; please delete non-functioning instances.

(I don't expect you to mess up your instance but mistakes happen!)

Should should select the latest "comp2406-2024f-" image as the starting image. This one will have deno already installed in the student account. If you use another image, you'll have to manually install deno and add its binary to the current path.

Once you have an openstack VM setup (with a floating IP assigned), you'll need to access it. The way you should do it is by using ssh (secure shell).

Connecting to your OpenStack VM via ssh

There are two basic ways to connect to an openstack VM: via a terminal, or via a remote desktop. Both will use ssh, but will use it in different ways.

If you do remote code editing using a local editor (such as Emacs or Visual Studio Code), under the hood it will be connecting to the VM via ssh (basically through a terminal).

Because of firewalls, you cannot connect to openstack VMs from the open Internet directly; you have to do it via the Carleton network. You can do this either through

• The Carleton network VPN, or by
• Connecting via ssh to another Linux system that allows ssh from the Internet.

SCS supports access to its Linux servers using their SCS accounts. So if your SCS username is JaneDoe, you can run in a terminal on your system:

 ssh janedoe@access.scs.carleton.ca

and, after typing in your password, you can access this machine.

For this class you don't want to use access directly; however, you can use it to "jump" to your openstack VM (avoiding the need for a VPN. So the basic ways to connect, if your username is janedoe and your VM's IP address is 134.117.33.1:

 ssh student@134.117.33.1     <--- while connected to the Carleton VPN

     or

 ssh -J janedoe@access.scs.carleton.ca student@134.117.33.1   <--- with no VPN

In this latter case, you'll be typing in your SCS password and your VM's password, which gets annoying quickly.

Default password: The default password for openstack VMs is "student" (for the student account). You'll have to change it when you first log in.

Avoiding passwords: For a guide to how to use ssh without passwords see SCS's guide.

ProxyJump config: If you put the following in a .ssh/options file on your machine, something like this:

Host jumphost
   User janedoe              # replace with your SCS username
   HostName access.scs.carleton.ca

Host comp2406
   User student
   Hostname 134.117.33.1    # replace with your VM's IP address
   ProxyJump jumphost

Then you can just type the following to access the VM without being on the Carleton VPN:

 ssh comp2406

Hello, World!

In your editor of choice, create a file hello.js in your Documents folder in your openstack VM with the following contents:

  console.log("Hello World!");

You can now run this file by typing:

  cd Documents           # if that is where you put your hello.js
  deno run hello.js

And you should see Hello, World! output to your terminal.

You can also run deno interactively by simply running deno with no arguments. You'll then get a prompt where you can enter any code that you like and see what it does. To exit this environment, type Control-D.

Note that when run interactively, we say that deno is running a read-eval-print loop (REPL). It reads input, evaluates it, and then prints the results. This structure is very old in computer science, going back to the first LISP interpreters from the early 1960's.