Tutorial: Chatter

DUE Wed, 09/10, 2 pm

Image: Free Icon, ChatGPT

This tutorial may be completed individually or in teams of at most 2. You can partner differently for each tutorial.

In this tutorial, users use the Chatter app to post textual chatts to our backend chatterd. The backend stores each chatt in a database and shares all posted chatts with everyone else accessing the backend. Treat messages you send to chatterd and Ollama as public utterances with no reasonable expectation of privacy and know that these are recorded and shared with everyone who uses chatterd.

This second tutorial builds on the first one, so if you haven’t completed the first one, you should do so first.

Expected behavior

Posting a new chatt:

Objectives

Front end:

• how to submit HTTP GET, in addition to POST, asynchronously
• how to convert to/from JSON manually

Back end:

• How to set up a PostgreSQL database and table
• How to interface URL path handlers with PostgreSQL

APIs and protocol handshakes

Chatter is a simple CRUD app. We’ll use the chatts table we will create in PostgreSQL to hold posted chatts. In this tutorial, we add two APIs to Chatter:

• postchatt: uses HTTP POST to post a chatt as a JSON object.
• getchatts: uses HTTP GET to query the database and retrieve all posted chatts,

Chatter does not provide “replace” (HTTP PUT) and “delete” (HTTP DELETE) functions.

Using this syntax:

url-endpoint
-> request: data sent to Server
<- response: data sent to Client

The protocol handshakes consist of:

/postchatt
-> HTTP POST { username, message }
<- {} 200 OK

/getchatts
-> HTTP GET {}
<- [ array of chatts ] 200 OK

Data formats

We associate a username with each message in a chatt. To post a chatt with the postchatt API, the front-end client sends a JSON Object consisting of "username" and "message". For example:

{	
   "username": "YOUR_UNIQNAME",	
   "message": "Hello world!"	
}

The getchatts API sends back all posted chatts as a JSON Array of string arrays (that is, an array or arrays). Each string array consists of four elements, in order: “username”, “message”, “id”, and “timestamp”. These are unkeyed. For example:

[ 
    ["username0", "message0", "id0", "timestamp0"],
    ["username1", "message1", "id1", "timestamp1"], 
    ... 
]

Each element of the string array may have a value of JSONNull.

Specifications

As in the previous tutorial, you only need to build one frontend, AND one of the alternative back-end stacks. Until you have a working backend of your own, you can use mada.eecs.umich.edu to test your front end. To receive full credit, your frontend MUST work with your own backend.

• Chatter Android

• Chatter iOS

The main addition to the chatterd backend is the use of PostgreSQL as permanent store and additional chatter APIs to insert to and retrieve from the store.

• Chatter Backend