Explain HTTP status codes

As a software engineer, it's crucial to understand how different parts of a system communicate. Let's discuss HTTP status codes. Can you explain what HTTP status codes are, their purpose, and provide some examples of common status codes and what they signify? Please elaborate on the different classes of status codes (1xx, 2xx, 3xx, 4xx, and 5xx) and what general situations they indicate. Also, can you provide some specific examples of codes within each class, such as 200, 404, 500, and explain what they mean in practical terms?

HTTP Status Codes

HTTP status codes are three-digit numerical codes returned by a server in response to a client's request. They provide information about the outcome of the request. These codes are grouped into five classes, indicated by the first digit:

• 1xx (Informational): The request was received and is being processed. These are rarely used directly.
• 2xx (Success): The request was successful.
• 3xx (Redirection): Further action is required to complete the request.
• 4xx (Client Error): The request contains bad syntax or cannot be fulfilled.
• 5xx (Server Error): The server failed to fulfill an apparently valid request.

Let's break down some of the most common and important status codes:

2xx Success

• 200 OK: The request was successful. This is the standard response for successful HTTP requests.
• 201 Created: The request has been fulfilled and resulted in a new resource being created. Often returned after a POST or PUT request.
• 204 No Content: The server successfully processed the request, but is not returning any content. This is often used for DELETE requests.

3xx Redirection

• 301 Moved Permanently: The requested resource has been permanently moved to a new URL. Clients should update their bookmarks and links.
• 302 Found (Moved Temporarily): The requested resource has been temporarily moved to a different URL. Clients should continue to use the original URL for future requests.
• 304 Not Modified: Used for caching. It indicates that the resource has not been modified since the last time the client requested it. The client can use its cached copy.

4xx Client Error

• 400 Bad Request: The server cannot understand the request due to malformed syntax.
• 401 Unauthorized: Authentication is required, but the user has not provided credentials.
• 403 Forbidden: The server understood the request, but refuses to authorize it. The user does not have permission to access the resource, even with authentication.
• 404 Not Found: The server cannot find the requested resource. This is a very common error.
• 405 Method Not Allowed: The method specified in the request is not allowed for the resource identified by the request URI.
• 429 Too Many Requests: The user has sent too many requests in a given amount of time ("rate limiting").

5xx Server Error

• 500 Internal Server Error: A generic error message, given when an unexpected condition was encountered and no more specific message is suitable.
• 502 Bad Gateway: The server, while acting as a gateway or proxy, received an invalid response from another server.
• 503 Service Unavailable: The server is currently unavailable (because it is overloaded or down for maintenance). Generally, this is a temporary state.
• 504 Gateway Timeout: The server, while acting as a gateway or proxy, did not receive a timely response from another server.

Understanding HTTP status codes is crucial for debugging web applications and ensuring proper communication between clients and servers. These codes provide valuable information about the success or failure of a request, allowing developers to take appropriate actions to resolve issues.