An in-depth study of HTTP status codes and their classification

In-depth understanding of HTTP protocol status codes and their classification

HTTP protocol status codes are used to indicate the server’s processing results of requests during the HTTP request and response process. A kind of logo. The status code consists of three digits and is divided into five categories, namely 1xx, 2xx, 3xx, 4xx and 5xx. In this article, we will take a deeper look at the specific meaning and usage scenarios of these status codes, and provide corresponding code examples.

1xx status code: Informational status code
1xx status code indicates that the server has received the request and is processing it, but further operations are required. The more common status codes are:

• 100 Continue: Indicates that the server has received the header information of the request, and the client should continue to send the remaining part of the request.
• 101 Switching Protocols: Indicates that the server has understood and accepted the client's request, and will switch to a new protocol for communication.

Code example:

HTTP/1.1 100 Continue
HTTP/1.1 101 Switching Protocols

2xx class status code: Success status code
2xx class status code indicates that the server successfully received, understood, and processed the request. Common status codes are:

• 200 OK: Indicates that the request is successful.
• 201 Created: Indicates that the request was successful and the server has created a new resource.
• 204 No Content: Indicates that the request was successful, but the server did not return any content.

Code example:

HTTP/1.1 200 OK
HTTP/1.1 201 Created
HTTP/1.1 204 No Content

3xx class status code: Redirect status code
3xx class status code indicates that the browser needs to perform further operations to complete the request. Common status codes are:

• 301 Moved Permanently: Indicates that the requested resource has been permanently moved to a new location.
• 302 Found: Indicates that the requested resource is temporarily moved to a new location.
• 304 Not Modified: Indicates that the resource has not been modified and the cached version is used.

Code example:

HTTP/1.1 301 Moved Permanently
HTTP/1.1 302 Found
HTTP/1.1 304 Not Modified

4xx class status code: Client error status code
4xx class status code indicates that the request sent by the client has an error. Common status codes include:

• 400 Bad Request: Indicates that the request sent by the client has a syntax error.
• 401 Unauthorized: Indicates that the request is unauthorized and requires user authentication.
• 403 Forbidden: Indicates that the request was rejected by the server.
• 404 Not Found: Indicates that the requested resource does not exist.

Code example:

HTTP/1.1 400 Bad Request
HTTP/1.1 401 Unauthorized
HTTP/1.1 403 Forbidden
HTTP/1.1 404 Not Found

5xx class status code: Server error status code
5xx class status code indicates that an error has occurred within the server. Common status codes include:

• 500 Internal Server Error: Indicates that the server encountered an unexpected error.
• 502 Bad Gateway: Indicates that the server received an invalid response from the upstream server when acting as a gateway or proxy.
• 503 Service Unavailable: Indicates that the server is temporarily unable to process the request, usually due to server overload or shutdown for maintenance.

Code sample:

HTTP/1.1 500 Internal Server Error
HTTP/1.1 502 Bad Gateway
HTTP/1.1 503 Service Unavailable

By having an in-depth understanding of HTTP protocol status codes and their classification, we can better handle various situations that may occur during HTTP requests and responses. In actual development, the reasonable use of appropriate status codes can improve the reliability and performance of the system. We hope that the code examples provided in this article can help readers better understand and apply HTTP protocol status codes.

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