PROGRAMMING FOR THE WEB: THE INTERNET
WEB PROTOCOLS

Key Concepts in HTTP:

1. Client-Server Model

• Client: Typically a web browser that sends requests to the server. E.g. Google Chrome

• Server: A computer that hosts the website or web application and responds to client requests. E.g. Flask server.

2. Request-Response Cycle

• Client sends a request: When you type a URL or click a link, your browser sends an HTTP request.

• Server processes the request: The server (e.g., your Flask application) receives and processes the request.

• Server sends a response: The server sends back an HTTP response, usually containing the requested content.

• Client processes the response: Your browser renders the received content (HTML, CSS, JavaScript).

4. HTTP Methods

HTTP defines several request methods that indicate the desired action to be performed on the identified resource. 

• GET: Retrieve data from the server (e.g., loading a webpage)

• POST: Submit data to be processed by the server (e.g., submitting a form)

• PUT: Update an existing resource on the server

• DELETE: Request the server to delete a specified resource
  
  

We have used two of these in our Flask applications: GET and POST. E.g.

@app.route('/resource', methods=['GET', 'POST'])

def handle_resource():

    if request.method == 'POST':

        # Handle POST request

    else:

        # Handle GET request

5. Status Codes

HTTP responses include status codes that indicate the outcome of the request. Here are some common ones:

• 200 OK: Standard response for successful HTTP requests

• 201 Created: Request has been fulfilled, resulting in the creation of a new resource

• 301 Moved Permanently: This and all future requests should be directed to the given URI

• 404 Not Found: The requested resource could not be found

• 403 Forbidden: The server understood the request but refuses to authorize it

• 500 Internal Server Error: A generic error message when an unexpected condition was encountered

6. Headers

HTTP headers allow the client and server to pass additional information with the request or response. Common headers include:

• Content-Type: Indicates the media type of the resource (e.g., text/html, application/json)

• User-Agent: Contains information about the client software

• Cookie: Contains stored HTTP cookies

• Authorization: Contains credentials for authenticating the client with the server

7. Query Parameters and Request Body

• Query Parameters: Additional data sent in the URL (e.g., ?key1=value1&key2=value2)

• Request Body: Data sent in the body of POST or PUT requests

5. SSL and TLS