Build your own not-quite-Twitter!

This starter code implements users (with login/sessions), and freets so that you may focus on implementing your own design ideas.

The project is structured as follows:

• index.ts sets up the database connection and the Express server
• /freet contains files related to freet concept
  • collection.ts contains freet collection class to wrap around MongoDB database
  • middleware.ts contains freet middleware
  • model.ts contains definition of freet datatype
  • router.ts contains backend freet routes
  • util.ts contains freet utility functions for transforming data returned to the client
• /user contains files related to user concept
  • collection.ts contains user collection class to wrap around MongoDB database
  • middleware.ts contains user middleware
  • model.ts - contains definition of user datatype
  • router.ts - contains backend user routes
  • util.ts contains user utility functions for transforming data returned to the client
• /public contains the code for the frontend (HTML/CSS/browser JS)

Make a copy of this repository under your personal GitHub account by clicking the Use this template button. Make sure to enable the Include all branches option.

If you did not take 6.031 in Fall 2021 or Spring 2022, to ensure that your machine has the necessary software for the assignment, please follow Steps 1, 2, 5, and 6 on this page from the 6.031 website (now 6.1020).

• Navigate to the root folder of your cloned repository.
• Run source demo-setup.sh to set up the demo branches.
• Check your local branches with git branch; you should have one new branch, with a new commit.
  • view-demo demos how to extend functionality of a resource
• If everything looks good, run git push --all origin. At this point, you should see the demo branch at https://github.com/<username>/<repo-name>/branches (and the view-demo-code branch can now be deleted!)
• Now, if you navigate to the commit history of this branch (https://github.com/<username>/<repo-name>/commits/<branch-name>), you can click on the "demo:" commit and see exactly what we changed for each demo!

Follow the instructions here to add your fritter project to MongoDB Atlas.

After following the instructions above, you should have copied a secret that looks something like mongodb+srv://xxxxxx:[email protected]/?retryWrites=true&w=majority. Note that this allows complete access to your database, so do not include it anywhere that is pushed to GitHub or any other publicly accessible location.

To allow your local server to connect to the database you just created, create a file named .env in the project's root directory with the contents

MONGO_SRV=mongodb+srv://xxxxxx:[email protected]/?retryWrites=true&w=majority

where the secret is replaced with the one you obtained.

After finishing setup, we recommend testing both locally running the starter code, and deploying the code to Vercel, to make sure that both work before you run into issues later. The instructions can be found in the following two sections.

Firstly, open the terminal or command prompt and cd to the directory for this assignment. Before you make any changes, run the command npm install to install all the packages in package.json. You do not need to run this command every time you make any changes, unless you add a new package to the dependencies in package.json.

Finally, to test your changes locally, run the command npm start in the terminal or command prompt and navigate to localhost:3000 and interact with the frontend to test your routes.

We will be using Vercel to host a publicly accessible deployment of your application.

1. Create a fork of this repository through GitHub. This will create a repository in your GitHub account with a copy of the starter code. You'll use this copy to push your work and to deploy from.

2. Create a Vercel account using your GitHub account.

3. After you log in, go to the project creation page and select Continue with GitHub and give Vercel the permissions it asks for.

4. Find the repository you just created and click Import. For the Framework Preset, choose Other. In the Environment Variables section, add an entry where NAME is MONGO_SRV and VALUE is your MongoDB secret.

5. Click Deploy and you will get a link like https://fritter-starter-abcd.vercel.app/ where you can access your site.

Vercel will automatically deploy the latest version of your code whenever a push is made to the main branch.

The data that Fritter stores is divided into modular collections called "resources". The starter code has only two resources, "freets" and "users". The codebase has the following:

• A model file for each resource (e.g. freet/model.ts). This defines the resource's datatype, which defines the resource's backend type, and should be a distilled form of the information this resource holds (as in ADTs). This also defines its schema, which tells MongoDB how to store our resource, and should match with the datatype.
• A collection file for each resource (e.g. freet/collection.ts). This defines operations Fritter might want to perform on the resource. Each operation works on the entire database table (represented by e.g. FreetModel), so you would operate on one Freet by using FreetModel.findOne().
• Routes file (e.g. freet/router.ts). This contains the Fritter backend's REST API routes for freets resource, and interact with the resource collection. All the routes in the file are automatically prefixed by e.g. /api/freets.
• Middleware file (e.g freet/middleware.ts). This contains methods that validate the state of the resource before performing logic for a given API route. For instance isFreetExists in freet/middleware.ts ensures that a freet with given freetId exists in the database

To add a resource or edit functionality of an existing resource:

• Create/modify files in the four above categories, making sure you have one model file, one collection one router file, and one middleware file per resource.
  • It helps to go in the order that they're listed above, starting with the resource's datatype.
• In freet/utils.ts and user/utils.ts there are type definitions for frontend representations of resources, and functions to convert from a backend resource type. Create/modify these as necessary.
  • An example: the frontend type definition for User lacks a password property, because the frontend should never be receiving users' passwords.

For this assignment, we provide an extremely basic frontend for users to interact with the backend. Each box (html form) represents exactly one API route, with a textbox for each parameter that the route takes.

To add a new route to the frontend, two components need to be added: a form in public/index.html and a corresponding event handler in public/scripts/index.js. The form will allow the user to input any necessary fields for the route, and the event handler will take the values of these fields and make an API call to your backend.

For example, the form for the user creation route looks like:

<form id="create-user">
    <h3>Create User</h3>
    <div>
        <label for="username">Username:</label>
        <input id="username" name="username">
    </div>
    <div>
        <label for="password">Password:</label>
        <input id="password" name="password">
    </div>
    <input type="submit" value="Create User">
</form>

In public/scripts/user.js, there is an event handler for this form (event handlers are separated in files by concept, currently user.js and freet.js), which makes a POST request to the backend:

function createUser(fields) {
  fetch('/api/users', {method: 'POST', body: JSON.stringify(fields), headers: {'Content-Type': 'application/json'}})
    .then(showResponse)
    .catch(showResponse);
}

Here, fields is a JSON object which contains key/value pairs, where the key is the name associated with the input field in the form and the value is whatever is entered on the frontend. For instance, in the form above, the first input field has name, username, which will be a key in fields object whose value is whatever has been entered as the username on the frontend. Thus, whatever name you attach to any input field is the same name you will can use to access the value entered in that input field from fields object.

To link the form and event handler together, there is an entry in the formsAndHandlers object (the key is the id attribute of the <form> tag and the value is the event handler function) in public/scripts/index.js:

const formsAndHandlers = {
  'create-user': createUser,
  ...
};

MongoDB is how you will be storing the data of your application. It is essentially a document database that stores data as JSON-like objects that have dynamic schema. You can see the current starter code schema in freet/model.ts and user/model.ts.

You will be using Mongoose, a Node.js-Object Data Modeling (ORM) library for MongoDB. This is a NoSQL database, so you aren't constrained to a rigid data model, meaning you can add/remove fields as needed. The application connects to the MongoDB database using Mongoose in index.ts, where you see mongoose.connects(...). After it connects, you will be able to make mongoose queries such as FindOne or deleteMany.

In this starter code, we have provided user and freet collections. Each collection has defined schemas in */model.ts. Once you defined a Schema, you must create a Model object out of the schema. The instances of your model are what we call "documents", which is what is stored in collections. Each schema maps to a MongoDB collection and defines the shape and structure of documents in that collection, such as what fields the document has. When a schema is defined, documents in the collection must follow the schema structure. You can read more about documents here.

To create a new Schema, you first need to define an interface which represents the type definition. You can then create a new Schema object by declaring const ExampleSchema = new Schema<Example>(...) where Example is the type definition on the backend. Then, you can create a model like const ExampleModel = model<Example>("Example", ExampleSchema). You can see a more detailed schema in the model.ts files mentioned above.

Mongoose allows you to use schema validation if you want to ensure that certain fields exist. For example, if you look at freet/model.ts, you will find fields like

  content: {
    type: String,
    required: true
  }

within the schema. This tells us that the content field must have type String, and that it is required for documents in that collection. A freet must have a String type value for the content field to be added to the freets collection.

The following api routes have already been implemented for you (Make sure to document all the routes that you have added.):

This renders the index.html file that will be used to interact with the backend

Body

• username {string} - The user's username
• password {string} - The user's password

Returns

• A success message
• The user's details (without password)

Throws

• 403 if the user is already logged in
• 400 if username or password is not in correct format format or missing in the req
• 401 if the user login credentials are invalid

Returns

• A success message

Throws

• 401 if user is not logged in

Body

• username {string} - The user's username
• password {string} - The user's password

Returns

• A success message
• The created user's details (without password)

Throws

• 403 if there is a user already logged in
• 400 if username or password is in the wrong format
• 409 if username is already in use

Body (no need to add fields that are not being changed)

• username {string} - The user's username
• password {string} - The user's password

Returns

• A success message
• The updated user details (without password)

Throws

• 401 if the user is not logged in
• 400 if username or password is in the wrong format
• 409 if the username is already in use

Returns

• A success message

Throws

• 401 if the user is not logged in

Returns

• An array of all freets sorted in descending order by date modified

Returns

• An array of freets created by user with username author

Throws

• 400 if author is not given
• 404 if author is not a recognized username of any user

Body

• parent {freetId} - The freet being replied to (optional)
• content {string} - The content of the freet

Returns

• A success message
• The created freet

Throws

• 401 if the user is not logged in
• 404 if parent is present but is not a recognized id of any freet
• 400 If the freet content is empty or a stream of empty spaces
• 413 If the freet content is more than 140 characters long

Returns

• A success message

Throws

• 401 if the user is not logged in
• 403 if the user is not the author of the freet
• 404 if the freetId is invalid

Returns

• A success message
• The user's details (without password)
• An array of users who follow the user
• An array of users whom the user is following

Throws

• 400 if username is not given
• 404 if username is not a recognized username of any user

Body

• username {string} - The username of the account to follow

Returns

• A success message

Throws

• 401 if the user is not logged in
• 400 if username is not given
• 404 if username is not a recognized username of any user
• 409 if the user already follows username

Returns

• A success message

Throws

• 401 if the user is not logged in
• 400 if username is not given
• 404 if username is not the username of a followed user

Returns

• An array of sources of the feed, sorted in ascending order by username
• An array of freets from the feed, sorted in descending order by date modified

Throws

• 401 if the user is not logged in
• 400 if name is not given
• 404 if name is not a recognized name of any of the user's feeds

Body

• name {string} - The name of the feed

Returns

• A success message
• The created feed's details

Throws

• 401 if the user is not logged in
• 400 if name is empty or a stream of empty spaces
• 409 if the user already has a feed with name name

Body

• add {array) - The sources to add to the feed (optional)
• remove {array} - The sources to remove from the feed (optional)

Returns

• A success message
• The updated feed's details

Throws

• 401 if the user is not logged in
• 400 if name is not given
• 404 if name is not a recognized name of any of the user's feeds
• 400 if both add and remove are missing or empty
• 400 if either add or remove is present and isn't an array
• 404 if a source in add or remove is not the username of any user
• 409 if a source in add is already a source of the feed
• 404 if a source in remove is not a source of the feed

Returns

• A success message

Throws

• 401 if the user is not logged in
• 400 if name is not given
• 404 if the name is not a recognized name of any of the user's feeds
• 400 if the user tries to delete the "Following" feed

Returns

• An object with the following fields
  • lineage of the freet
  • details of the freet
  • children of a freet, sorted in descending order by relevance rating

Throws

• 400 if freetId is not given
• 404 if freetId is invalid