HTTP status codes are issued by a server in response to a client's request made to the server. They provide information about the status of the request. Here are some common HTTP status codes and their meanings:
- 1xx Informational:
- 100 Continue: The server has received the initial part of the request, and the client should proceed with the rest of the request.
- 2xx Success:
- 200 OK: The request was successful, and the server has returned the requested data.
- 201 Created: The request was successful, and a new resource was created as a result.
- 204 No Content: The server successfully processed the request, but there is no content to send in the response.
- 3xx Redirection:
- 301 Moved Permanently: The requested resource has been permanently moved to a new location, and future requests should use the new URL.
- 302 Found (or 303 See Other): The requested resource has been temporarily moved to a different location. The client should continue to use the original URL for future requests.
- 304 Not Modified: The client's cached copy of the resource is still valid, and there is no need to re-download it.
- 4xx Client Errors:400 Bad Request: The server could not understand the request due to malformed syntax or other client-side errors.
- 401 Unauthorized: The request requires user authentication. The client must provide valid credentials.
- 403 Forbidden: The server understood the request, but the server refused to authorize it.
- 404 Not Found: The server cannot find the requested resource.
- 5xx Server Errors:500 Internal Server Error: A generic error message indicating that the server has encountered an unexpected condition and cannot fulfil the request.
- 501 Not Implemented: The server does not support the functionality required to fulfil the request.
- 502 Bad Gateway: The server, while acting as a gateway or proxy, received an invalid response from an upstream server.
- 503 Service Unavailable: The server is not ready to handle the request. Common causes include temporary overloading or maintenance of the server.
- 504 Gateway Timeout: The server, while acting as a gateway or proxy, did not receive a timely response from an upstream server or some other auxiliary server it needed to access in order to complete the request.
These codes are part of the HTTP protocol and help both clients and servers understand the outcome of a request. They are crucial for troubleshooting and understanding the status of web transactions.