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In this section, we will delve into the core of RESTful API development: handling requests and responses. This involves understanding how to process incoming requests from clients and how to formulate appropriate responses. We'll cover the following key concepts:

Understanding HTTP Requests and Responses
Parsing Request Data
Formulating Responses
Practical Examples
Exercises

Understanding HTTP Requests and Responses

HTTP Requests

An HTTP request is a message sent by a client to a server to perform a specific action. It consists of:

Request Line: Contains the HTTP method (e.g., GET, POST), the URI, and the HTTP version.
Headers: Provide metadata about the request (e.g., content type, authorization).
Body: Contains the data sent to the server (used mainly in POST, PUT, PATCH methods).

HTTP Responses

An HTTP response is a message sent by the server back to the client. It consists of:

Status Line: Contains the HTTP version, status code, and status message.
Headers: Provide metadata about the response (e.g., content type, content length).
Body: Contains the data sent back to the client.

Parsing Request Data

When a server receives a request, it needs to parse the data to understand what the client is asking for. This involves:

Extracting Path Parameters: Parameters included in the URL path.
Extracting Query Parameters: Parameters included in the URL query string.
Extracting Headers: Metadata included in the request headers.
Extracting Body Data: Data included in the request body (usually in JSON format).

Example: Extracting Data in Node.js with Express

const express = require('express');
const app = express();

app.use(express.json()); // Middleware to parse JSON body

app.get('/users/:id', (req, res) => {
    const userId = req.params.id; // Extracting path parameter
    const filter = req.query.filter; // Extracting query parameter
    const authHeader = req.headers['authorization']; // Extracting header

    res.send(`User ID: ${userId}, Filter: ${filter}, Authorization: ${authHeader}`);
});

app.post('/users', (req, res) => {
    const userData = req.body; // Extracting body data
    res.send(`User Data: ${JSON.stringify(userData)}`);
});

app.listen(3000, () => {
    console.log('Server is running on port 3000');
});

Formulating Responses

Once the server processes the request, it needs to send back a response. This involves:

Setting Status Codes: Indicating the result of the request (e.g., 200 OK, 404 Not Found).
Setting Headers: Providing metadata about the response.
Sending Body Data: Sending the actual data back to the client.

Example: Sending Responses in Node.js with Express

app.get('/users/:id', (req, res) => {
    const userId = req.params.id;

    // Simulate fetching user data
    const user = { id: userId, name: 'John Doe' };

    if (user) {
        res.status(200).json(user); // Sending a 200 OK response with JSON data
    } else {
        res.status(404).send('User not found'); // Sending a 404 Not Found response
    }
});

Practical Examples

Example 1: Handling a GET Request

app.get('/products', (req, res) => {
    const products = [
        { id: 1, name: 'Laptop' },
        { id: 2, name: 'Phone' }
    ];
    res.status(200).json(products);
});

Example 2: Handling a POST Request

app.post('/products', (req, res) => {
    const newProduct = req.body;
    // Simulate saving the product
    newProduct.id = Date.now();
    res.status(201).json(newProduct); // Sending a 201 Created response
});

Exercises

Exercise 1: Handling PUT Requests

Create an endpoint to update a product's information.

app.put('/products/:id', (req, res) => {
    const productId = req.params.id;
    const updatedProduct = req.body;

    // Simulate updating the product
    updatedProduct.id = productId;

    res.status(200).json(updatedProduct);
});

Exercise 2: Handling DELETE Requests

Create an endpoint to delete a product.

app.delete('/products/:id', (req, res) => {
    const productId = req.params.id;

    // Simulate deleting the product
    res.status(204).send(); // Sending a 204 No Content response
});

Solutions

Solution 1: Handling PUT Requests

app.put('/products/:id', (req, res) => {
    const productId = req.params.id;
    const updatedProduct = req.body;

    // Simulate updating the product
    updatedProduct.id = productId;

    res.status(200).json(updatedProduct);
});

Solution 2: Handling DELETE Requests

app.delete('/products/:id', (req, res) => {
    const productId = req.params.id;

    // Simulate deleting the product
    res.status(204).send(); // Sending a 204 No Content response
});

Conclusion

In this section, we covered the essentials of handling requests and responses in a RESTful API. We learned how to parse request data, formulate responses, and implemented practical examples using Node.js and Express. By mastering these concepts, you are now equipped to handle various types of requests and responses in your RESTful API development. Next, we will explore authentication and authorization to secure your API endpoints.

Handling Requests and Responses