What is HTTP?

The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, and hypermedia information systems. It forms the foundation of data communication for the World Wide Web. This protocol follows a client-server model, where an HTTP client opens a connection and sends a request message to an HTTP server; the server then returns a response message, usually containing the resource that was requested.

What is in an HTTP request?

An HTTP request is a message sent by the client to initiate an action on the server. Here’s a simplified example of how an HTTP request looks like:

GET /index.html HTTP/1.1
Host: www.example.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) Firefox/89.0
Accept: text/html

The components of this HTTP request are:

Request Line: This is the first line of the request. It contains the HTTP method (GET), the request target (/index.html), and the HTTP version (HTTP/1.1). Headers: These are key-value pairs that provide additional information about the request. In this example, Host specifies the domain, User-Agent provides details about the client’s operating system and browser, and Accept specifies the type of data the client can process. Body (Optional): Not shown in this example, the body of a request contains data that the client wants to send to the server. This is commonly used in POST requests.

What is an HTTP method?

An HTTP method is a verb that indicates the desired action to be performed on the specified resource. The most popular ones are:

  • GET: Requests a representation of the specified resource.
  • POST: Submits data to be processed by the specified resource.
  • PUT: Replaces the current representation of the target resource with the uploaded content.
  • DELETE: Removes the specified resource.

What are HTTP request headers?

HTTP request headers are part of the HTTP request, providing additional parameters and information to the server about the request.

Here’s how a set of HTTP request headers might look like:

Host: www.example.com
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) Firefox/89.0
Accept: text/html

These headers tell the server where the request is meant to go (Host), what browser and operating system made the request (User-Agent), and what type of content the client will accept in response (Accept).

What is in an HTTP request body?

The HTTP request body is used to send data to the server. The data contained in the body depends on the type of request. For example, a POST request, used to create new resources, often includes a body that contains the data for the new resource.

Here’s a simplified example of an HTTP POST request with a JSON payload in the body:

POST /api/users HTTP/1.1
Host: www.example.com
Content-Type: application/json

{
  "username": "new_user",
  "email": "[email protected]"
}

The body (the part after the blank line) is sending JSON data to create a new user.

What is in an HTTP response?

An HTTP response is what is sent by the server in reply to an HTTP request from a client. Here’s an example of a simple HTTP response:

HTTP/1.1 200 OK
Date: Sat, 04 Jun 2023 12:00:00 GMT
Content-Type: text/html
Content-Length: 137

<html>
<body>
<h1>Hello, World!</h1>
</body>
</html>

The components of this HTTP response are:

  • Status Line: This is the first line of the response. It contains the HTTP version (HTTP/1.1), the status code (200), and the status text (OK).
  • Headers: These provide additional information about the response or the requested resource. In this example, Date is the date and time the message was sent, Content-Type specifies the type of the returned content, and Content-Length provides the size of the returned content in bytes.
  • Body: This is the requested resource itself, which comes after a blank line. In this example, the body contains an HTML document.

What’s an HTTP status code?

An HTTP status code is a standard response code given by website servers on the internet. The codes help identify the cause of the problem when a web page or other resource does not load properly. Here are some of the most popular HTTP status codes:

  • 200 OK: This is the standard response for successful HTTP requests.
  • 404 Not Found: The server has not found anything matching the requested resource.
  • 500 Internal Server Error: A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.
  • 301 Moved Permanently: The URL of the requested resource has been changed permanently.

What are HTTP response headers?

HTTP response headers, as part of the HTTP response, provide additional information about the response or the requested resource.

Here’s how a set of HTTP response headers might look like:

Date: Sat, 04 Jun 2023 12:00:00 GMT
Content-Type: text/html
Content-Length: 137

These headers tell when the response was sent (Date), what the media type of the response body is (Content-Type), and how many bytes are in the body (Content-Length).

What is in an HTTP response body?

The HTTP response body is where the requested resource, along with any additional embedded resources, is returned. If you request an HTML page, the HTML and any additional resources (such as images or scripts) will be in the response body. Here’s an example of a simple HTML document in a response body:

<html>
<body>
<h1>Hello, World!</h1>
</body>
</html>

Can DDoS attacks be launched over HTTP and how can a reverse proxy help?

Yes, Distributed Denial-of-Service (DDoS) attacks can be launched over HTTP. These attacks are designed to overwhelm a server with traffic, rendering it unable to respond to legitimate requests.

One common form of DDoS is an HTTP flood attack, where an attacker sends a large number of HTTP requests in an attempt to overwhelm the server’s resources.

A reverse proxy can help mitigate these attacks by distributing incoming requests across multiple servers, thus reducing the impact of the traffic surge on any single server. It can also help by providing additional layers of validation and protection, such as rate limiting (to prevent a client from sending too many requests) and IP filtering (to block traffic from suspicious IPs).