HTTP Messages.
HTTP messages are how clients and servers communicate. They encapsulate requests and responses, conveying information necessary for the exchange of data. HTTP messages adhere to a well-defined structure, consisting of headers and, in the case of message bodies, the payload.
Types of HTTP Messages.
HTTP (Hypertext Transfer Protocol) messages come in two primary types: Request messages and Response messages. Let's understand each each type:
1. HTTP Request Messages.
HTTP request messages are sent by clients to request a specific action or resource from a server. These messages provide information about the desired operation, including the HTTP method, the target resource, headers, and, in some cases, a message body.
Component of HTTP Request Message.
Request Line: The Request Line in HTTP is the initial line of an HTTP request message that provides essential information about the client's intended action. It consists of three components:
- HTTP Method: Specifies the type of request or action the client wants to perform (e.g., GET, POST, PUT).
- Target Resource (URI or URL): Specifies the resource on the server that the client is requesting.
- HTTP Version: Indicates the version of the HTTP protocol being used in the request.
Example:
GET /index.html HTTP/1.1Headers: Provide additional information about the request, such as the Host, User-Agent, and Accept headers.
Example:
Host: www.example.com User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/91.0.4472.124 Safari/537.36 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
- Host: Specifies the domain name or IP address of the server.
- User-Agent: Identifies the client software and its version.
- Accept: Informs the server about the types of media that the client can process.
Message Body: Optional and used for sending data with certain HTTP methods like POST or PUT.
Example:
POST /submit-form HTTP/1.1
Host: www.example.com
Content-Type: application/x-www-form-urlencoded
Content-Length: 27
username=johndoe&password=1232. HTTP Response Messages.
HTTP response messages are sent by servers to provide the outcome of the client's request. These messages include information about the server's response, such as the HTTP version, status code, headers, and an optional message body.
Component of HTTP Response Message.
Status Line: Specifies the HTTP version, a three-digit status code, and a reason phrase.
Note: A status code is a three-digit numeric code returned by a server to indicate the outcome of a client's request. Status codes are an integral part of HTTP responses, providing information about the success, failure, or other circumstances surrounding the request.
Example:
HTTP/1.1 200 OK
Headers: Provide additional information about the response, such as Content-Type, Content-Length, and Server headers.
Example:
Content-Type: text/html
Content-Length: 1234
Server: Apache/2.4.29 (Ubuntu)
Message Body: Contains the actual data being sent in response to the client's request.
Example:
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 5678
<!DOCTYPE html>
<html>
<head>
<title>Example Page</title>
</head>
<body>
<h1>Hello, World!</h1>
</body>
</html>
The request-response cycle in HTTP is used for communication where a client sends a request to a server, and the server responds by providing the requested information or performing the specified action.
Common HTTP Methods.
HTTP messages use various methods (or verbs) to indicate the desired action. Some common methods include:
- GET: Retrieve data from the server. It is a safe and idempotent method, meaning multiple identical requests should have the same effect as a single request.
- POST: Submit data to be processed to a specified resource. It often results in the creation of a new resource on the server.
- PUT: Update a resource on the server or create it if it does not exist. It replaces the entire resource with the submitted data.
- DELETE: Request the removal of a resource on the server.
- HEAD: Retrieve only the headers of a resource without the actual data, useful for checking the resource's metadata.
- OPTIONS: Retrieve information about the communication options available for a resource.
- PATCH: Apply partial modifications to a resource. It is often used to update specific fields in an existing resource.
- TRACE: Echoes the received request, allowing the client to see what changes or additions occurred during its journey to the server.
These methods provide a standardized way for clients to interact with resources on the web, enabling various operations like retrieving, creating, updating, or deleting data.
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